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Amino acid synthesis pathway in animals

Amino acid synthesis pathway in animals

Retrieved 28 July acic Contact us Amino acid synthesis pathway in animals enquiries: Access here and click Contact Us General enquiries: info biomedcentral. A Guide synthesiss the Principles of Animal Nutrition Copyright © by Gita Cherian is licensed under a Creative Commons Attribution-NonCommercial 4. For example, rats can down- or up-regulate AA-catabolic and urea-cycle enzymes in response to a low or high intake of AAs [ 14 ].

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Overview of Amino Acid Metabolism

Amino acid synthesis pathway in animals -

Among the array of metabolites at the interface between these microorganisms and the host is the essential aromatic amino acid tryptophan Agus et al. We are delighted by the updated information on aromatic amino acid metabolism covered in the articles of our research topic.

A review by Parthasarathy et al. included in this topic, describes the aromatic amino acid biosynthetic pathways in plants and microbes, catabolism in plants, degradation via the monoamine and kynurenine pathways in animals, and catabolism via the 3-aryllactate and kynurenine pathways in animal-associated microbes.

L-Tyrosine is an aromatic amino acid synthesized de novo in plants and microbes via two alternative routes mediated by a TyrA family enzyme, prephenate, or arogenate dehydrogenase, typically found in microbes and plants, respectively.

In the research article by Schenck et al. it was revealed that bacterial homologs, closely-related to plant TyrAs, also have an acidic residue at position and arogenate dehydrogenase activity as the plant enzyme does, which indicates that the conserved molecular mechanism operated during the evolution of arogenate-specific TyrAa in both plants and microbes.

Tryptophan is another aromatic amino acid, which can be oxidized by tryptophan 2,3-dioxygenase and indoleamine 2,3 dioxygenase in the initial step in tryptophan catabolism in animals and humans.

Although these two enzymes catalyze the same reaction, the assembly of the catalytically active, ternary enzyme-substrate-ligand complexes is not yet fully resolved.

Nienhaus and Nienhaus summarized present knowledge of ternary complex formation in tryptophan 2,3-dioxygenase and indoleamine 2,3 dioxygenase and related these findings to structural peculiarities of their active sites. Aromatic amino acids can also be oxidized by phenylalanine, tyrosine, or tryptophan hydroxylase, and then decarboxylated by aromatic amino acid decarboxylases to form aromatic monoamines.

The N-acylation of the aromatic monoamines by arylalkylamine N-acyltransferases is mostly associated with the acetylation of serotonin to form N-acetylserotonin, a precursor in the formation of melatonin Hardeland and Poeggeler, ; Mukherjee and Maitra, Insects express more arylalkylamine N-acyltransferases in order to regulate aromatic amino acid metabolism Hiragaki et al.

For example, 13 putative arylalkylamine N-acyltransferases have been identified in Aedes aegypti Han et al. O'Flynn et al. In the final review article of this special issue, Liang et al. All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Funding was provided by the National Natural Science Foundation of China Grant No. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Agus, A. Gut microbiota regulation of tryptophan metabolism in health and disease. Cell Host Microbe 23, — doi: PubMed Abstract CrossRef Full Text Google Scholar.

Amherd, R. Purification, cloning, and characterization of a second arylalkylamine N-acetyltransferase from Drosophila melanogaster. DNA Cell. Braus, G. Aromatic amino acid biosynthesis in the yeast Saccharomyces cerevisiae : a model system for the regulation of a eukaryotic biosynthetic pathway.

PubMed Abstract Google Scholar. Dempsey, D. Mechanistic and structural analysis of Drosophila melanogaster arylalkylamine N-acetyltransferases. Biochemistry 53, — Han, Q. Evolution of insect arylalkylamine N-acetyltransferases: structural evidence from the yellow fever mosquito, Aedes aegypti.

Crystal structure of human kynurenine aminotransferase II. Hardeland, R. Non-vertebrate melatonin. Pineal Res. Healy-Fried, M. Structural basis of glyphosate tolerance resulting from mutations of Pro in Escherichia coli 5-enolpyruvylshikimatephosphate synthase. Hiragaki, S. Structures and functions of insect arylalkylamine N-acetyltransferase iaaNAT ; a key enzyme for physiological and behavioral switch in arthropods.

Mukherjee, S. Gut melatonin in vertebrates: chronobiology and physiology. Selvan, S. Indoleamine 2,3-dioxygenase IDO : biology and target in cancer immunotherapies.

The requirement for certain amino acids will vary depending on the species, gender, diet and stage of life of the animal. For example, lysine and methionine are typical first-limiting amino acids in dairy cows.

Identifying this first-limiting amino acid is extremely important for production purposes since animals cannot reach production levels of protein synthesis without sufficient quantities of first-limiting amino acids; no matter how much lysine you feed a dairy cow, if methionine is the first-limiting amino acid, the animal may not synthesize enough proteins to produce the desired quantities of milk.

For this reason, providing sufficient amounts of all essential amino acids in the diets of production animals is paramount. If an animal is not provided sufficient quantities of certain essential amino acids in its diet, the animal cannot produce enough proteins to support certain metabolic functions.

From a production standpoint, failing to provide enough amino acids in an animal's diet will result in reduced overall performance, which can significantly reduce profitability.

Here are just a few problems associated with inadequate supply of amino acids for livestock:. One of the first and most important signs of an amino acid imbalance in the feed of a herd is a reduction in feed intake. Although most animals will initially eat more food to try to compensate for the deficiency, after a few days the animals will decrease their food intake substantially.

This decrease in intake occurs because amino acid imbalances in food result in reduced hunger in many species. This can contribute to further nutritional deficiencies and subsequently lead to low performance and health problems. In both young and adult animals, amino acid deficiencies contribute to low body weight and a general reduction in muscle development.

For younger animals, this can have long-lasting effects, including a reduced growth rate, a prolonged time to reach maturity and reduced size at maturity. This low body weight cannot be fixed through force-feeding 3.

Studies have shown that even when animals are forced to eat sufficient calories if the diet is missing amino acids, the animal will still experience morphological problems and will often continue to lose weight.

In dairy cows, an inadequate supply of amino acids will result in reduced milk production. In poultry, an overall reduction in the size and quantity of eggs produced has been reported. Amino acids are the building blocks of tissues and milk proteins, so that any deficiency will reduce production.

Amino acids are essential for animal health, contributing to the maintenance of numerous metabolic functions, including maintenance and immune responses. If certain amino acids are missing from an animal's diet, it may experience reduced immune and metabolic responses, leaving its body more vulnerable to diseases, and, in severe cases, mortality.

Although amino acid deficiencies can result in low performance and health problems, they can be prevented through dietary manipulations, such as adjusting the types and quantities of the various common feeds. However, these adjustments have limitations because the traditional feeds vary in amino acid composition, and their combination may not always achieve the correct proportion of amino acids required to maintain production and health of the animal.

The use of specific proteins or amino acids offers a more flexible and targeted solution for manipulating animal diets to achieve the required level and ratios of amino acids.

One of the biggest challenges with supplementing amino acids to ruminants cows, goats and sheep is the rumen, or first stomach. The rumen is the habitat to many microbes that ferment almost any feed or compound that is not protected. So, if unprotected amino acids are fed to ruminants, they will be degraded by the rumen microbes, which may be a waste.

To manage this problem and ensure that ruminants get the amino acids they need in adequate quantities, animal health and nutrition companies have found ways to feed amino acids directly to the small intestine.

This is often accomplished by employing two mechanisms:. Rumen Protection: Rumen-protected amino acids are protected from the environment of the rumen so that they can reach the small intestine more consistently while avoiding degradation.

Intestinal Availability: Amino acids are useless if the intestine can't absorb them after passing through the rumen. Some amino acid products fail to release the amino acid at this point, and the amino acid is excreted in the feces. To avoid this, feed producers have developed products that release the rumen-protected amino acid after passing through the rumen so that it can be absorbed in the intestine.

Historically, blood meal has been used to get lysine through the rumen and into the bloodstream, but this product tended to be unreliable and often resulted in the excretion of excess nitrogen into the environment.

Numerous feeding trials over the past several decades have shown that protein supplements can increase production for milk and eggs in livestock and poultry, respectively.

While the exact mechanism and amino acid balances differ based on the species and type of feed being used, cows, sheep and chickens all exhibited increased production when fed increased amounts of amino acids in their respective diets. For cattle and sheep specifically, introducing more dietary protein and a better amino acid makeup to cows can increase milk production substantially.

Depending on diet, the limiting amino acids for milk production can be methionine, lysine or any other amino acid. However, research suggests that increasing overall amino acid availability to the small intestine results in an increase in production attributed to the increased availability of disposable non-essential amino acids.

In cows specifically, the delivery of high-quality protein with a well-balanced spread of amino acids was seen to produce a curvilinear increase in milk production 4 , leveling out as the cows reached their genetic limits.

Studies of egg-laying hens found similar results when fed more amino acids. Hens consistently produced more eggs of larger sizes. Unlike cows and sheep, hens do not have a rumen to consider, so unprotected amino acids can be added directly to the diet.

Typically, methionine tends to be the limiting amino acid in the diets of laying hens, and ideally they each should be fed around mg of methionine per day 5 to achieve maximum production.

Lysine and arginine are also highly significant in their diet, though it is equally important for hens to be fed enough pure caloric energy to produce since egg-laying is energetically expensive. During the early phases of growth, all animals need access to as many essential amino acids as possible, as they need to produce sufficient proteins to support their growing bodies.

Studies have shown that an increase in protein intake directly corresponds to an increase in protein deposition 6 within the bodies of growing animals, resulting in stronger, healthier mature animals. Some amino acids are slightly more important than others, however.

Amino Acids for Ruminates: For calves, the most important amino acids are methionine, lysine, isoleucine, threonine and leucine. A deficiency in any of these amino acids results in a slowing of growth and delayed onset of maturity. The most important of these, methionine, is an essential amino acid.

Though used inefficiently from a biological standpoint, methionine is important in cattle and sheep as a methyl group donor and a precursor for cysteine synthesis. Lysine is the second most limiting amino acid for growing calves, especially in maize-based diets because maize is relatively low in lysine.

Amino Acids for Pigs: Pigs have similar needs to calves, with the notable exception being arginine. While arginine is not an essential amino acid since it can be synthesized from glutamate and glutamine, it is essential to younger piglets in the neonatal and immediate postweaning phases.

Forty percent of pigs' arginine requirements 7 must be supplied through their diet, primarily due to their rapid growth rates and the fact that most arginine is used in the urea cycle of the liver. Amino Acids for Poultry: Growing poultry require similar amino acid balances as other growing animals, but they require arginine in their diets because they do not have a urea cycle and therefore cannot synthesize it on their own.

A deficiency of arginine often results in feather deformation in chickens 8. Lysine deficiencies can negatively affect feather growth in turkeys as well. Nutrition has a significant effect on the quality of eggs in all animals.

From the emergence of ovarian follicles through embryonic development, undernutrition can have a devastating effect on reproductive health for farm animals. By feeding animals sufficient amounts of amino acids to support egg production and embryonic health, you can ensure that your animals are producing healthy offspring at an optimal rate.

In ruminants, under-nutrition of amino acids can have a negative effect on fertility, especially during early ovulation.

Most prominently, the intake of methionine and lysine have a strong effect throughout the fertility cycle. These two amino acids are particularly important for embryonic development and consuming too little of either nutrient can negatively impact fertility.

In one study, feeding rumen-protected methionine during the peripartum period of a cow's cycle significantly improved postpartum performance. Additionally, studies have found that pregnancies are healthier when cows are fed sufficient amounts of methionine and lysine through the pregnancy, especially on days nine through 19, during which the cow's body determines whether to continue with a pregnancy.

Pigs require a balanced diet that contains plenty of essential and non-essential amino acids. While essential amino acids are important to support a pregnancy, sows also require dietary glutamine and arginine 9 to support mucosal integrity and neonatal growth, respectively.

In summary, amino acids play varying importance roles based on the species of farm animal, its age and its production purpose. Across all factors, however, protein supplements for cattle, pigs and poultry can deliver promising results and improve the performance and profitability of an animal.

Here are just a few ways that essential amino acids for animal health can benefit your bottom line:. When you raise the protein level in farm animal feed, farm animals will eat more food and digest it more efficiently, in turn increasing the amounts of amino acids and nutrients available to the animal.

This also improves feed efficiency, so there is less waste. Appropriate amino acid balances support improved growth rate so that animals will wean and reach mature weight early.

Additionally, well-fed calves, piglets and chicks tend to be healthier and larger as adults, producing more and experiencing disease at a lower rate. The most prominent reason for culling cows is reproduction — if a cow doesn't calve, it doesn't produce milk. Conversely, the higher an animal's production potential, the higher the value of the pregnancy.

By increasing the amount and the quality of amino acids in feed, especially methionine and lysine, studies have shown an improvement in pregnancy rates 10 , which not only contribute to herd numbers but also improve milk production, increasing profitability.

Regardless of how much a cow is producing, it costs the same to keep it in the herd due to operating costs, fixed overhead costs, maintenance requirements and dry matter.

To make the most of that cow, it is important that she produces enough milk to offset any costs of increasing feed quality.

Amino acid synthesis is the pathday of natural abdominal fat loss processes metabolic pathways by oathway Amino acid synthesis pathway in animals amino acids are produced. The substrates for synthrsis processes are various compounds in the organism 's diet or growth media. Not all organisms are able to synthesize all amino acids. For example, humans can synthesize 11 of the 20 standard amino acids. These 11 are called the non-essential amino acids.

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De novo pathwy of animaps and taurine is very syntheeis in cats. Syntheais, concentrations of both taurine and arginine in feline milk are the greatest among domestic pthway.

Compared with dogs, cats have greater endogenous nitrogen Amino acid synthesis pathway in animals and Amink dietary requirements znimals many amino acids e. Adequate intakes synthedis high-quality protein i. Pet-food grade animal-sourced foodstuffs are excellent sources of both proteinogenic amino acids symthesis taurine synthssis cats and dogs, and can help to optimize their growth, development, syntnesis health, Amino acid synthesis pathway in animals.

Synthesiss animals contribute Aino the mental animls and well-being of children, adolescents, and anomals, and have become dynthesis popular in many countries and worldwide over the past decades Table 1. In the United States, BCAA supplements for reducing muscle fatigue Most ppathway are commercially manufactured, animala some people choose Cranberry breakfast ideas prepare meals for their own pets by ahimals animal- and animlas ingredients.

Thus, the pathwaay petfood industry has grown substantially in recent aanimals. The compound annual patuway rate of the global aicd market is acie to be avid. The cat, which was also from the order Carnivora, is the synthesie domesticated species in the family Ysnthesis [ 7 ].

The feline domestication occurred Stay hydrated during intense workouts 10, anijals ago [ 7 ]. To date, im dog ani,als [ 8 ] and synrhesis cat aciid [ animaks ] ysnthesis differences in shape, size, and acif are recognized pathwsy.

Both cats and dogs have: a acud relatively shorter digestive Amio, longer canine synthesiz, and a tighter digitation of molars than omnivorous mammals such as humans and paghway, b a Dark chocolate satisfaction low activity of salivary Artichoke appetizer ideas, c a limited Sleep and nutrition for athletes to synthesize de novo arginine and vitamin D or to synthessi α-linolenic acid to 5,8,11,14,17,docosahexaenoic acid, A,ino d instinct preferences for meat to plant products [ 1011 ].

Based Post-game muscle recovery their anatomical, metabolic, and natural feeding characteristics, dogs animas carnivores A,ino cats obligate carnivores are classified as carnivores in classic Aminl BCAA supplements for reducing muscle fatigue [ ajimals ] and veterinary medicine [ 13 Amino acid synthesis pathway in animals textbooks, but snthesis animals acic evolved axid have animal unique feeding behaviors and metabolic characteristics that are distinct from mAino mammals such patway pigs, Aminl, and humans [ synthssis1415 ].

Synnthesis National Research Council NRC [ 16 ] recognizes that the dog is a carnivore anatomically but has many metabolic characteristics of omnivores, including the synthhesis of β-carotene to vitamin A, tryptophan to niacin, cysteine to taurine, Amino acid synthesis pathway in animals linoleic acid to syntesis acid.

Pathwsy also differ from cats in many of these syntthesis. Regardless of their sources of food, adequate knowledge of nutrient metabolism and requirements by cats pathwsy dogs is crucial to ensure their pathwy growth, animxls, and health.

The major objective pathwxy this article is to highlight the nutrition and metabolism payhway amino acids AAs in cats and dogs. Pathwqy indicated, AAs except for glycine and taurine refer to the L -isomers herein. Determination of AA digestibilities synthseis cats and aicd usually requires a 5-d period of adaptation and a 5-d pathwayy of sample collection [ synthesiss ].

Amino acid synthesis pathway in animals date, the fecal Amink method has acis largely synthexis to measure the apparent psthway tract digestibilities of AAs in cats, and some studies have involved Ammino collection at the end of anjmals ileum in dogs [ 17181920 Amio.

Data on total tract digestibilities Athlete weight loss amino acids wcid not useful for formulating Ankmals diets, but comparison between apparent ileal and synthess tract AA digestibilities may synthesjs to assess the pathay of metabolism ln individual AAs in the large intestine [ 15 ].

Although there are substantial amounts of endogenous AAs in the syntnesis intestine synthessis both cats and dogs Table 2 due to gastrointestinal secretions such as sloughed patwhay and digestive aanimals [ lathway2223annimals ], there are synthesiis data Aminoo the true ileal digestibilities of Ppathway and other nutrients pathwau these synthsis due to both technical and aciv challenges.

Nevertheless, standardized ileal digestibilities of scid AAs based amimals corrections for endogenous AA flow in Amino acid synthesis pathway in animals ileum have kn reported for dogs [ 15 ].

Animas to published studies [ 25 animalz, 26 ], standardized ileal digestibilities of AAs parhway dogs are similar to, or lower than, those for pigs Table 3. Accid with dogs, cats Real-time blood glucose monitoring have Consistent power solutions apparent digestibilities of AAs for lower-quality proteins due to a shorter small intestine relative to body weight BW but have similar values for high-quality proteins e.

The cecectomized rooster model has been used to assess the digestibilities of AAs in foodstuffs for cats and dogs [ 28 ]. Based on this assay, a very low true digestibility of glycine e.

In addition, results from a study with a swine model indicated that the apparent ileal digestibility of cysteine and proline i. Caution over data accuracy and test animal models should be taken when interpreting and using literature data on AA digestibilities for feeding companion animals. Many of the factors that influence apparent AA digestibilities in dogs have similar effects in cats.

In manufacturing pet foods, the heating of plant-sourced foodstuffs destroys trypsin inhibitors, but prolonged heating decreases the digestibilities of crude protein CP and AAs e. Cooking can result in improved digestibilities of AAs in dogs [ 30 ] and of starch in cats [ 31 ].

Increasing the dietary level of soluble fiber reduces CP digestibility in both dogs [ 3233 ] and cats [ 31 ]. Comparisons between the apparent ileal and total tract digestibilities of methionine and lysine in dogs indicate that, in contrast to pigs [ 38 ], a a substantial amount of protein metabolites is absorbed by the canine large intestine and b the microbes of the canine large intestine do not have a net synthesis of methionine and lysine.

These findings suggest an important difference in gut microbial metabolism among animal species. Digestibilities of AAs are influenced by the breed and age of dogs, as well as diet and the method of its preparation. Likewise, no difference in CP digestibility was noted between 2- and year-old beagles [ 41 ].

Dietary supplementation with β-mannanase the enzyme hydrolyzing polysaccharides made from D -mannose enhanced the apparent digestibilities of CP in dogs fed a diet containing a large amount of plant-sourced protein ingredients, but had no effect in dogs fed a diet containing a large amount of animal-sourced protein ingredients [ 42 ].

Compared with the extruded diet, slight cooking enhanced CP digestibility in dogs [ 30 ]. Likewise, the inclusion of 7. Hair, which is lost from the skin, should be removed from feces for accurately measuring nutrient digestibility in cats [ 25 ].

Harper and Turner [ 44 ] reported that week-old cats had higher apparent CP digestibilities than younger kittens. However, the apparent digestibility of dietary CP was decreased in cats fed raw corn starch and raw potato starch compared with cooked foods [ 46 ].

These results indicate effects of age and dietary composition on the digestion of dietary protein and microbial AA metabolism in the gut. The metabolism of most AAs by cats and dogs is similar to that of other mammals [ 43 ].

In support of this view, the plasma concentrations of most AAs from different research groups [ 47484950 ] are similar between adult cats and dogs, except for Asn, Asp, Citrulline, Glu, Gly, His and Pro that are lower in dogs than in cats and for lysine that is higher in dogs than in cats Table 4.

Interestingly, the plasma concentrations of Arg, citrulline, and ornithine in both cats and dogs were lower than those for pigs [ 5152 ] Table 4suggesting differences in the whole-body metabolism of AAs among the three animal species.

The qualitative dietary requirements of dogs for most AAs are similar to those for omnivores e. However, in contrast to most breeds of dogs, cats have a very limited ability to synthesize taurine and arginine [ 14 ].

Because taurine is present in animal products but absent from plants [ 54 ], cats must be provided with at least a portion of animal-sourced foods or the same essential nutrients from synthetic supplements [ 43 ].

This is consistent with the much greater concentrations of both taurine and arginine in the milk of cats [ 55565758 ] as compared with ruminants and pigs Table 5 [ 596061 ].

Thus, there are peculiar differences in the requirements of certain AAs, such as taurine essential for tissue integrity [ 62 ] and arginine essential for maintaining the urea cycle in an active state [ 63 ] between cats and dogs.

Likewise, the concentrations of many AAs in plasma differ between cats and dogs offered diets high in carbohydrate, high in fat, or high in protein [ 64 ].

Cats and dogs chose a different mix of food, which is consistent with cats needing a higher protein concentration in food than dogs [ 64 ]. In these two animal species, the synthesis of glucose from AAs in the liver and kidneys plays an important role in maintaining glucose homeostasis [ 43 ].

When diets do not provide sufficient starch, glycogen or glucose, dogs must synthesize glucose from glucogenic AAs in their liver and kidneys [ 65 ]. In contrast to modern breeds of dogs that consume both animal- and plant-sourced foods, a natural food i.

Thus, in cats, gluconeogenesis from AAs plays an essential role in the provision of glucose to the brain, red blood cells, and immunocytes, and therefore their survival [ 12 ]. In adult dogs BW ranging from 2. This is equivalent to the catabolism of 1.

There was no significant effect of either sex or BW on the measured variables expressed per metabolic BW, but endogenous urinary nitrogen output was positively correlated with BW loss during the d feeding period [ 66 ]. The endogenous excretions of total, urea, ammonia, and creatinine a metabolite of creatine nitrogen for cats fed the protein-free diet were, Similarly, Earle [ 68 ] reported that adult cats could maintain nitrogen balance or had minimal endogenous nitrogen loss at 1.

These values are greater than those for dogs and pigs Table 2. Accordingly, adult cats require 2 to 3 times more dietary protein than adult dogs and herbivores e.

For comparison, a dietary intake of protein energy accounting for 3. The obligatory loss of nitrogen in cats appears to be similar when they are fed a nitrogen-free diet or are food deprived [ 16 ]. Interestingly, nitrogen balance in adult cats fed a low-protein diet may be maintained when lean body mass is reduced [ 71 ], possible due to reduced oxidation of AAs in a tissue-specific manner [ 61 ].

This must be taken into consideration when determining AA requirements of cats. There have been many studies of arginine nutrition in dogs since the pioneering work of Rose and Rice in [ 72 ]. In adult dogs [ 7374 ], as in many other adult mammals e.

The small intestine and other organs of dogs express arginase for the hydrolysis of arginine to urea and ornithine [ 75 ]. Unlike pigs [ 61 ], the small intestine of postabsorptive dogs does not release arginine [ 73 ], likely due to either low activities of argininosuccinate synthase and lyase for arginine synthesis or the further hydrolysis of arginine by arginase in enterocytes.

Thus, the homeostasis of arginine in the body depends on the rates of its endogenous synthesis and catabolism. Growing and adult dogs cannot synthesize sufficient arginine to meet functional needs e.

Thus, a dietary level of 0. This indicates that both mature and immature dogs have an inadequate or limited ability to synthesize arginine de novo. Syndromes of arginine deficiency in dogs include decreased food intake, hyperammonemia, severe emesis, frothing at the mouth, and muscle tremors, and can be prevented by dietary supplementation with arginine or citrulline [ 16 ].

Dietary or arterial blood ornithine is not used for arginine synthesis and cannot correct arginine deficiency symptoms in dogs [ 43 ]. When fed a milk-replacer diet containing inadequate arginine, dog puppies develop cataract [ 77 ].

Dietary arginine deficiency also occurs in human infants causing hyperammonemia and death and adults [reducing nitric oxide NO synthesis, sperm production, and fetal growth], and in rats impairing growth and spermatogenesis [ 61 ].

Cats have a very limited ability to synthesize citrulline and arginine de novo because of the low activities of pyrrolinecarboxylate P5C synthase and ornithine aminotransferase [ 78 ]. The latter also limits the formation of citrulline from proline via the proline oxidase pathway.

There is evidence for the synthesis of arginine from citrulline and the catabolism of arginine via arginase in feline renal tubules [ 79 ].

Dietary supplementation with citrulline or ornithine to cats can prevent hyperammonemia due to arginine deficiency. However, citrulline, but not ornithine, can restore growth in young cats fed an arginine-free diet [ 80 ].

Such results can be explained by the findings that dietary or arterial blood ornithine is not used for the intestinal synthesis of citrulline in cats [ 63 ], as reported for other mammals including dogs [ 73 ] and pigs [ 53 ]. This is due to both the preferential metabolism of dietary ornithine into proline by enterocytes and the lack of uptake of arterial blood ornithine by the gut [ 63 ].

We suggest that higher protein requirements by cats than dogs may result, in part, from a much lower ability to synthesize arginine in cats. In canine and feline nutrition, aspartate, glutamate, and glutamine are among the traditionally classified nutritionally nonessential AAs NEAAsbut this has been disputed [ 81 ].

: Amino acid synthesis pathway in animals

Editorial: Aromatic Amino Acid Metabolism

All plants and micro-organisms synthesize their own aromatic amino acids to make proteins Braus, ; Tzin and Galili, However, animals have lost these costly metabolic pathways for aromatic amino acids synthesis and must instead obtain the amino acids through their diet.

Herbicides take advantage of this by inhibiting enzymes involved in aromatic amino acid synthesis, thereby making them toxic to plants but not to animals Healy-Fried et al. Tyrosine is the initial precursor for the biosynthesis of dopa, dopamine, octopamine, norepinephrine, and epinephrine, etc.

In addition, tyrosine is the precursor for melanin synthesis in most organisms including humans and animals, and is particularly important in insects for protection Whitten and Coates, Tryptophan is the initial precursor for the biosynthesis of tryptamine, serotonin, auxin, kynurenines, and melatonin Hardeland and Poeggeler, ; Mukherjee and Maitra, Kynurenic acid, a kynurenine, produced along the tryptophan-kynurenine pathway, is an antagonist at excitatory amino acid receptors and plays a role in protecting neurons from overstimulation by excitatory neurotransmitters Han et al.

Many enzymes involved in aromatic amino acids metabolism have been drug targets for diseases including neurodegenerative diseases, schizophrenia, and cancers Stone and Darlington, ; Selvan et al. In addition, since animals or humans that do not possess the enzymatic machinery for the de novo synthesis of aromatic amino acids must obtain these primary metabolites from their diet, the metabolism of aromatic amino acid by both the host animal and the resident microflora are important for the health of humans and all animals.

Among the array of metabolites at the interface between these microorganisms and the host is the essential aromatic amino acid tryptophan Agus et al. We are delighted by the updated information on aromatic amino acid metabolism covered in the articles of our research topic. A review by Parthasarathy et al.

included in this topic, describes the aromatic amino acid biosynthetic pathways in plants and microbes, catabolism in plants, degradation via the monoamine and kynurenine pathways in animals, and catabolism via the 3-aryllactate and kynurenine pathways in animal-associated microbes. L-Tyrosine is an aromatic amino acid synthesized de novo in plants and microbes via two alternative routes mediated by a TyrA family enzyme, prephenate, or arogenate dehydrogenase, typically found in microbes and plants, respectively.

In the research article by Schenck et al. it was revealed that bacterial homologs, closely-related to plant TyrAs, also have an acidic residue at position and arogenate dehydrogenase activity as the plant enzyme does, which indicates that the conserved molecular mechanism operated during the evolution of arogenate-specific TyrAa in both plants and microbes.

Tryptophan is another aromatic amino acid, which can be oxidized by tryptophan 2,3-dioxygenase and indoleamine 2,3 dioxygenase in the initial step in tryptophan catabolism in animals and humans. Although these two enzymes catalyze the same reaction, the assembly of the catalytically active, ternary enzyme-substrate-ligand complexes is not yet fully resolved.

Nienhaus and Nienhaus summarized present knowledge of ternary complex formation in tryptophan 2,3-dioxygenase and indoleamine 2,3 dioxygenase and related these findings to structural peculiarities of their active sites.

Aromatic amino acids can also be oxidized by phenylalanine, tyrosine, or tryptophan hydroxylase, and then decarboxylated by aromatic amino acid decarboxylases to form aromatic monoamines.

The N-acylation of the aromatic monoamines by arylalkylamine N-acyltransferases is mostly associated with the acetylation of serotonin to form N-acetylserotonin, a precursor in the formation of melatonin Hardeland and Poeggeler, ; Mukherjee and Maitra, Insects express more arylalkylamine N-acyltransferases in order to regulate aromatic amino acid metabolism Hiragaki et al.

For example, 13 putative arylalkylamine N-acyltransferases have been identified in Aedes aegypti Han et al. O'Flynn et al. In the final review article of this special issue, Liang et al.

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Funding was provided by the National Natural Science Foundation of China Grant No. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Agus, A. Gut microbiota regulation of tryptophan metabolism in health and disease.

Cell Host Microbe 23, — These differences may reflect variations in AA composition of chickens reported in the literature. Because the content of proline plus hydroxyproline in the body of chickens was not known at that time, the relatively small amount of proline in the recommended ideal protein was only arbitrarily set and could limit responses of the animals to dietary EAA in their maximal growth and production performance.

In contrast, very large amounts of glutamate e. However, key questions regarding whether glutamate fulfilled this role and whether excess glutamate might interfere with the transport, metabolism and utilization of other AA in chickens were not addressed by the Illinois investigators [ 33 — 36 ].

Possibly due to these concerns and the publication of the NRC nutrient requirements for poultry in [ 37 ], Baker [ 38 ] did not include glutamate, glycine or proline in an ideal protein for diets of 0- to d-old chickens in his modified University of Illinois Ideal Ratios of Amino Acids for broiler chickens in Table 2.

Work on the ideal protein for poultry diets laid a foundation for subsequent studies with growing pigs. Thus, the British nutritionist Cole suggested in that swine diets could be formulated to contain ideal ratios of EAA with lysine as the reference AA based on their concentrations in the pig carcass almost exclusively tissue proteins [ 39 ].

This idea was adopted first by the British Agricultural Research Council ARC in [ 40 ] and then by the U. National Research Council NRC in [ 41 ]. Also, its conceptual foundation based solely on the EAA composition of the body was flawed, because the pattern of AA in the diet does not reflect the composition of AA in the animal [ 16 , 42 ].

This mismatch can be explained as follows: a individual AA in the diet undergo extensive catabolism and transformations at different rates in the small intestine; b the concentrations of AA in the circulation differ markedly from the relative abundance of AA in the diet; c individual AA in plasma have different metabolic fates in different animal tissues; and d the abundance of AA in tissue proteins differs greatly from that in the diet [ 2 , 16 , 43 ].

These major shortcomings limit the usefulness of the early versions of the ideal protein in formulating swine diets for maximal growth or production performance of pigs. Dietary AA are required by animals primarily for maintenance including the synthesis of nonprotein metabolites and protein accretion [ 2 ].

This was due, in part, to technical challenges to accurately determine maintenance requirements of AA, which include replacement of degraded proteins, as well as the use of AA for synthesis of low-molecular-weight substances and ATP production [ 1 ].

Between and , in attempts to improve the original ideal protein concept [ 39 , 40 ], T. Wang and M. Fuller [ 45 ] used gilts in the weight range of 25 to 50 kg to estimate an ideal pattern of dietary AA that included requirements for both maintenance and tissue protein accretion.

As for the studies with chickens in the s and s, there were also concerns over the assumptions for inclusion of this high level of glutamate in the swine diet that lacks all other NEAA.

While glutamate was used to prepare isonitrogenous diets in the previous studies, none of these investigators considered that animals have a dietary requirement of glutamate for optimal growth and production performance.

Having recognized the need to modify the ideal protein concept for formulating swine diets, D. Baker took great efforts between and to evaluate dietary requirements of EAA by 10—20 kg swine. In their original study, D. Baker and his student T. However, other synthesizable AA including alanine, aspartate, asparagine, cysteine, glutamine, serine, and tyrosine were not considered in the revised version of the ideal protein and the rationale for the use of arginine, glycine, histidine, and proline at different proportions to lysine was not explained [ 46 ].

Furthermore, the bases for other assumptions were unknown, including: a whether glutamate is an effective precursor for sufficient synthesis of all other AA including aspartate, glutamine, and serine in specific tissues e.

Furthermore, little attention was paid to inter-organ fluxes of amino acids relative to their intracellular metabolism. In addition, although intracellular glutamate is used to synthesize aspartate, many extra-intestinal tissues and cells e.

Over the past two decades, there have been successful attempts to refine the patterns of some AA in diets for lactating, suckling, weanling, finishing, and gestating pigs by addition of arginine [ 48 — 53 ], glutamine [ 54 — 59 ], glutamate [ 60 — 64 ], proline [ 65 — 67 ], or glycine [ 68 , 69 ], or by determining mammary gland growth, changes of whole-body AA composition, and milk yields in lactating sows [ 70 , 71 ].

The outcomes are increases in neonatal and postweaning growth, lactation performance, and litter size in pigs. Growing evidence shows that both EAA and NEAA e. arginine, glutamine, glutamate, glycine, and proline play important roles in regulating gene expression, cell signaling, nutrient transport and metabolism, intestinal microbiota, anti-oxidative responses, and immune responses [ 1 , 2 ].

Based on these lines of compelling evidence from animal studies, Wu and colleagues proposed the new concept of functional AA, which are defined as those AA that participate in and regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of the organisms [ 1 , 2 , 16 ].

Metabolic pathways include: a intracellular protein turnover synthesis and degradation and associated events; b AA synthesis and catabolism; c generation of small peptides, nitrogenous metabolites, and sulfur-containing substances e.

Notably, the concept of functional AA in nutrition has also been adopted for fish [ 72 — 74 ], poultry [ 75 — 79 ], and small laboratory animals e. Readers are referred to recent reviews and original research article on these new developments [ 24 , 84 — ].

The carbon skeletons of EAA including tyrosine and cysteine are not synthesized from non-AA substances in animals [ 2 ]. As noted previously, synthesis of NEAA from EAA in animals is inadequate for their maximal growth, milk production, and reproduction performance or for optimal development and health.

Thus, the traditional classification of AA as EAA or NEAA is purely a matter of definition. For example, emerging evidence shows that arginine, glutamine, glutamate, and glycine play important roles in regulating gene expression, cell signaling, antioxidative responses, and immunity [ 51 — 56 ].

Additionally, glutamate, glutamine, and aspartate are major metabolic fuels for enterocytes [ 6 ] and also regulate intestinal and neurological development and function [ 2 ]. In addition, glutamine is essential for ATP production, synthesis of nucleotides, expression of anti-oxidative genes, and redox signaling in enterocytes [ 57 ].

Furthermore, glutamate activates chemical sensing in the gastrointestinal tract and may inhibit degradation of both EAA and NEAA by intestinal microbes [ 2 , 60 ]. Finally, proline and arginine, which are major sources of ornithine for intestinal and placental synthesis of polyamines [ 42 ], are essential for DNA and protein synthesis and also participate in protein and DNA methylation, and, thus genetic and epigenetic regulation of cell growth and development [ 2 ].

Collectively, animals have dietary requirements for all synthesizable AA to achieve their full genetic potential for growth, development, reproduction, lactation, and resistance to infectious disease [ 21 ].

Composition of EAA in feed ingredients and true ileal digestibilities of EAA in swine [ 41 ] and poultry [ 37 , 90 ] have been published. As an initial step to define NEAA requirements by animals, we recently determined the composition of all protein-AA in major feedstuffs [ 86 ] and in animal tissues [ 21 ].

Based on the previous studies of AA biochemistry and nutrition including AA metabolism and tissue protein gains in poultry e. The values for 5- to kg young pigs are based primarily on consideration of: a the entry of dietary AA into the portal vein for day-old postweaning pigs, as compared to the accretion of AA in the body [ 16 ]; b the published data of Baker [ 47 ] and NRC [ 41 ] on dietary EAA requirements; and c the estimated rates of AA synthesis, catabolism and accretion in the body [ 2 , 16 , 88 ].

Second, optimal ratios of EAA in diets of older pigs are based on the suggestions of the NRC [ 41 ] and Baker [ 47 ] in that the ratios of tryptophan, sulfur-AA, and threonine to lysine all based on true digestibility of EAA increase slightly with age, whereas the ratios of other EAA to lysine are not altered substantially during postnatal development.

Third, this is the first time that NEAA are included in optimal ratios of dietary AA for pigs and poultry at various physiological stages.

This is based on the following considerations [ 2 ]: a BCAA are actively degraded in extra-hepatic and extra-intestinal tissues; b leucine can stimulate muscle protein synthesis in young pigs; c leucine, isoleucine and valine should be in an appropriate ratio to prevent AA imbalance; d large amounts of histidine-containing dipeptides are present in skeletal muscle; and e tyrosine is actively utilized in multiple metabolic pathways and its carbon skeleton is formed only from phenylalanine in animals.

The recommended values for EAA and NEAA requirements must be revised as new and compelling experimental data become available. Amino acids have versatile and important physiological functions beyond their roles as the building blocks of protein [ ].

Thus, dietary NEAA and EAA are necessary for the survival, growth, development, reproduction and health of animals. Growing evidence shows that pigs and poultry cannot synthesize sufficient amounts of all NEAA to achieve their maximum genetic potential [ 95 — ].

Additionally, glutamate, glutamine and aspartate are major metabolic fuels for the small intestine to maintain its digestive function and to protect its mucosal integrity. While metabolic needs for an AA by animals do not necessarily translate into its dietary needs, results of recent studies indicate that animals have both metabolic and dietary needs for AA that are synthesized in the body [ — ].

This new initiative will provide a much-needed framework for both qualitative and quantitative analysis of dietary requirements for all AA by livestock, poultry and fish through conduct of additional research.

Adoption of these recommended values in animal feeding are expected to beneficially reduce dietary protein content and improve the efficiency of nutrient utilization, growth, and production performance of farm animals. The concept of dietary requirements for NEAA also has important implications in human nutrition and health.

Wu G: Amino acids: metabolism, functions, and nutrition. Amino Acids. PubMed Google Scholar. Wu G: Amino Acids: Biochemistry and Nutrition. Google Scholar. Baker DH: Advances in protein-amino acid nutrition of poultry.

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Womack M: Amino acid feeding studies: effects of various nonessential nitrogen sources and of added water. Stucki WP, Harper AE: Importance of dispensable amino acids for normal growth of chicks. Maruyama K, Sunde ML, Harper AE: Is L-glutamic acid nutritionally a dispensable amino acid for the young chick?.

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Kim SW, Wu G: Regulatory role for amino acids in mammary gland growth and milk synthesis. Wu G, Meier SA, Knabe DA: Dietary glutamine supplementation prevents jejunal atrophy in weaned pigs. For example, a pregnant cow has different amino acid needs compared to a milk-producing cow because the protein quantities they require are slightly different.

The protein-producing potential of an animal is limited by the quantities of amino acids in its body. Since certain proteins require specific amino acids, if the body cannot synthesize enough of a single amino acid or it is not supplied in adequate amount in the diet, it will not be able to produce certain types of proteins required for certain processes.

The amino acid in shortest supply is referred to as the "first-limiting" amino acid in the diet. The requirement for certain amino acids will vary depending on the species, gender, diet and stage of life of the animal. For example, lysine and methionine are typical first-limiting amino acids in dairy cows.

Identifying this first-limiting amino acid is extremely important for production purposes since animals cannot reach production levels of protein synthesis without sufficient quantities of first-limiting amino acids; no matter how much lysine you feed a dairy cow, if methionine is the first-limiting amino acid, the animal may not synthesize enough proteins to produce the desired quantities of milk.

For this reason, providing sufficient amounts of all essential amino acids in the diets of production animals is paramount. If an animal is not provided sufficient quantities of certain essential amino acids in its diet, the animal cannot produce enough proteins to support certain metabolic functions.

From a production standpoint, failing to provide enough amino acids in an animal's diet will result in reduced overall performance, which can significantly reduce profitability. Here are just a few problems associated with inadequate supply of amino acids for livestock:.

One of the first and most important signs of an amino acid imbalance in the feed of a herd is a reduction in feed intake. Although most animals will initially eat more food to try to compensate for the deficiency, after a few days the animals will decrease their food intake substantially.

This decrease in intake occurs because amino acid imbalances in food result in reduced hunger in many species. This can contribute to further nutritional deficiencies and subsequently lead to low performance and health problems. In both young and adult animals, amino acid deficiencies contribute to low body weight and a general reduction in muscle development.

For younger animals, this can have long-lasting effects, including a reduced growth rate, a prolonged time to reach maturity and reduced size at maturity.

This low body weight cannot be fixed through force-feeding 3. Studies have shown that even when animals are forced to eat sufficient calories if the diet is missing amino acids, the animal will still experience morphological problems and will often continue to lose weight. In dairy cows, an inadequate supply of amino acids will result in reduced milk production.

In poultry, an overall reduction in the size and quantity of eggs produced has been reported. Amino acids are the building blocks of tissues and milk proteins, so that any deficiency will reduce production.

Amino acids are essential for animal health, contributing to the maintenance of numerous metabolic functions, including maintenance and immune responses. If certain amino acids are missing from an animal's diet, it may experience reduced immune and metabolic responses, leaving its body more vulnerable to diseases, and, in severe cases, mortality.

Although amino acid deficiencies can result in low performance and health problems, they can be prevented through dietary manipulations, such as adjusting the types and quantities of the various common feeds.

However, these adjustments have limitations because the traditional feeds vary in amino acid composition, and their combination may not always achieve the correct proportion of amino acids required to maintain production and health of the animal. The use of specific proteins or amino acids offers a more flexible and targeted solution for manipulating animal diets to achieve the required level and ratios of amino acids.

One of the biggest challenges with supplementing amino acids to ruminants cows, goats and sheep is the rumen, or first stomach. The rumen is the habitat to many microbes that ferment almost any feed or compound that is not protected.

So, if unprotected amino acids are fed to ruminants, they will be degraded by the rumen microbes, which may be a waste. To manage this problem and ensure that ruminants get the amino acids they need in adequate quantities, animal health and nutrition companies have found ways to feed amino acids directly to the small intestine.

This is often accomplished by employing two mechanisms:. Rumen Protection: Rumen-protected amino acids are protected from the environment of the rumen so that they can reach the small intestine more consistently while avoiding degradation. Intestinal Availability: Amino acids are useless if the intestine can't absorb them after passing through the rumen.

Some amino acid products fail to release the amino acid at this point, and the amino acid is excreted in the feces. To avoid this, feed producers have developed products that release the rumen-protected amino acid after passing through the rumen so that it can be absorbed in the intestine.

Historically, blood meal has been used to get lysine through the rumen and into the bloodstream, but this product tended to be unreliable and often resulted in the excretion of excess nitrogen into the environment.

Numerous feeding trials over the past several decades have shown that protein supplements can increase production for milk and eggs in livestock and poultry, respectively.

While the exact mechanism and amino acid balances differ based on the species and type of feed being used, cows, sheep and chickens all exhibited increased production when fed increased amounts of amino acids in their respective diets.

For cattle and sheep specifically, introducing more dietary protein and a better amino acid makeup to cows can increase milk production substantially. Depending on diet, the limiting amino acids for milk production can be methionine, lysine or any other amino acid. However, research suggests that increasing overall amino acid availability to the small intestine results in an increase in production attributed to the increased availability of disposable non-essential amino acids.

In cows specifically, the delivery of high-quality protein with a well-balanced spread of amino acids was seen to produce a curvilinear increase in milk production 4 , leveling out as the cows reached their genetic limits.

Studies of egg-laying hens found similar results when fed more amino acids. Hens consistently produced more eggs of larger sizes. Unlike cows and sheep, hens do not have a rumen to consider, so unprotected amino acids can be added directly to the diet.

Typically, methionine tends to be the limiting amino acid in the diets of laying hens, and ideally they each should be fed around mg of methionine per day 5 to achieve maximum production. Lysine and arginine are also highly significant in their diet, though it is equally important for hens to be fed enough pure caloric energy to produce since egg-laying is energetically expensive.

During the early phases of growth, all animals need access to as many essential amino acids as possible, as they need to produce sufficient proteins to support their growing bodies.

Studies have shown that an increase in protein intake directly corresponds to an increase in protein deposition 6 within the bodies of growing animals, resulting in stronger, healthier mature animals.

Some amino acids are slightly more important than others, however. Amino Acids for Ruminates: For calves, the most important amino acids are methionine, lysine, isoleucine, threonine and leucine.

A deficiency in any of these amino acids results in a slowing of growth and delayed onset of maturity.

Frontiers | Editorial: Aromatic Amino Acid Metabolism Breuer LH, Pond WG, Warner RG, Loosli JK: The role of dispensable amino acids in the nutrition of the rat. Types Bacterial Archaeal Eukaryotic. Consent for publication Not applicable. Abstract Domestic cats and dogs are carnivores that have evolved differentially in the nutrition and metabolism of amino acids. Clearly, animals have dietary requirements for not only EAA, but also NEAA to achieve maximum growth and production performance [ 21 — 23 ]. As an initial step to define NEAA requirements by animals, we recently determined the composition of all protein-AA in major feedstuffs [ 86 ] and in animal tissues [ 21 ]. Citation: Han Q, Phillips RS and Li J Editorial: Aromatic Amino Acid Metabolism.
5.14A: Amino Acid Synthesis Tryptophan-containing lipopeptide antibiotics derived from polymyxin B with activity against Gram positive and Gram negative bacteria. Knabe, Defa Li, Wilson G. The kynureninase of Pseudomonas fluorescens. Only in the breeds of dogs that possess sufficient enzymes for taurine synthesis can the adequate provision of methionine plus cysteine in their diets prevent metabolic diseases such as dilated cardiomyopathy. We have addressed this point above in our response to Essential Revision 3. Self selection of dietary casein and soy-protein by the cat. Article Google Scholar Stein HH, Pedersen C, Wirt AR, Bohlke RA.
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All proteins in the body are in a state of constant flux, the size of the amino acid pool depends on a balance between synthesis and degradation. In this chapter, amino acid metabolism involving protein and nonessential amino acid synthesis and disposal of toxic ammonia is discussed.

New Terms Citrulline Deamination Deoxyribonucleic acid DNA messenger RNA mRNA Ornithine Protein turnover Ribosomes Transamination transfer RNA tRNA Urea Uric acid Urea cycle. Absorbed proteins are used for anabolic purposes such as synthesis of nonessential amino acids, tissue protein synthesis, enzyme or hormone synthesis, deamination, or transamination.

The liver is the major site of amino acid metabolism. The liver has enzymes such as transaminases and is responsible for nonessential amino acid synthesis through a process called transamination. In this reaction, an amino group from one amino acid is transferred to an organic acid to form a new amino acid.

Vitamin B6 pyridoxine is needed for transaminase activity. Transamination also provides a link between protein and carbohydrate metabolism, where certain amino acids can use their C skeleton for glucose synthesis.

Deamination is the removal of amino groups from amino acids to form ammonia. After deamination or transamination, C skeletons are left and are used for making glucose, ketone bodies, or energy production.

All amino acids, except leucine and lysine, are glucogenic, meaning that they can use the C skeleton for glucose synthesis. Leucine and lysine are strictly ketogenic amino acids forms ketone bodies and can provide acetyl CoA as an energy source. Since both carbons of acetyl CoA are lost in the tricarboxylic acid TCA cycle, it cannot provide glucose.

Some amino acids isoleucine, phenylalanine, tyrosine, tryptophan are both glucogenic and ketogenic. All amino acids, except leucine and lysine, are glucogenic. Leucine and lysine are strictly ketogenic.

The ammonia liberated from amino acid degradation is toxic to the central nervous and needs to be excreted or detoxified. Most mammals detoxify ammonia and excrete it as urea in the urine, while birds excrete it as uric acid a white substance in the excreta.

The detoxification of ammonia to form urea is brought about by the urea cycle through two tissues liver and kidney; Figure Two nonprotein amino acids amino acids not used for protein synthesis involved in the urea cycle are ornithine and citrulline The first step in the urea cycle is the formation of carbamoyl phosphate through the condensation of ammonium ions with bicarbonate ions in the mitochondria of the liver.

Ornithine reacts with a compound called carbamoyl phosphate and forms citrulline. Citrulline is easily permeable and gets into the cytosol and reacts with aspartate, forming argininosuccinate 2 ATP needed.

The enzyme argininosuccinate lyase cleaves argininosuccinate into arginine and fumarate and fumarate enters the TCA cycle. Arginine is lysed into ornithine and splits urea off, producing ornithine, to start the cycle again. Hence arginine can be a nonessential amino acid but not available for protein synthesis.

The kidneys synthesize arginine from citrulline. The liver breaks down arginine into urea and ornithine. Poultry cannot synthesize carbamoyl phosphate and hence they cannot make urea.

Instead, glutamic acid, glycine, and methionine are used for uric acid synthesis. Hence poultry need high levels of methionine, arginine, and glycine in their diet for optimum production.

These proteins use a collection of metal ions as the electron carriers that are responsible for the reduction of N 2 to NH 3. All organisms can then use this reduced nitrogen NH 3 to make amino acids. In humans, reduced nitrogen enters the physiological system in dietary sources containing amino acids.

All organisms contain the enzymes glutamate dehydrogenase and glutamine synthetase, which convert ammonia to glutamate and glutamine, respectively.

Amino and amide groups from these two compounds can then be transferred to other carbon backbones by transamination and transamidation reactions to make amino acids. Interestingly, glutamine is the universal donor of amine groups for the formation of many other amino acids as well as many biosynthetic products.

Glutamine is also a key metabolite for ammonia storage. All amino acids, with the exception of proline, have a primary amino group NH 2 and a carboxylic acid COOH group. They are distinguished from one another primarily by , appendages to the central carbon atom.

Figure 2 Figure Detail In the study of metabolism, a series of biochemical reactions for compound synthesis or degradation is called a pathway. Amino acid synthesis can occur in a variety of ways. For example, amino acids can be synthesized from precursor molecules by simple steps. Alanine, aspartate, and glutamate are synthesized from keto acids called pyruvate, oxaloacetate, and alpha-ketoglutarate, respectively, after a transamination reaction step.

Similarly, asparagine and glutamine are synthesized from aspartate and glutamate, respectively, by an amidation reaction step. The synthesis of other amino acids requires more steps; between one and thirteen biochemical reactions are necessary to produce the different amino acids from their precursors of the central metabolism Figure 2.

The relative uses of amino acid biosynthetic pathways vary widely among species because different synthesis pathways have evolved to fulfill unique metabolic needs in different organisms.

Although some pathways are present in certain organisms, they are absent in others. Therefore, experimental results about amino acid metabolism that are achieved with model organisms may not always have relevance for the majority of other organisms. Not all the organisms are capable of synthesizing all the amino acids, and many are synthesized by pathways that are present only in certain plants and bacteria.

Mammals, for example, must obtain eight of twenty amino acids from their diets. This requirement leads to a convention that divides amino acids into two categories: essential and nonessential given a certain metabolism.

Because of particular structural features, essential amino acids cannot be synthesized by mammalian enzymes Reeds Nonessential amino acids, therefore, can be synthesized by nearly all organisms.

The loss of the ability to synthesize essential amino acids likely emerged very early in evolution, because this dependence on other organisms for the source of amino acids is common among all eukaryotes, not just those of mammals. How do certain amino acids become essential for a given organism?

Studies in ecology and evolution give some clues. Organisms evolve under environmental constraints, which are dynamic over time.

If an amino acid is available for uptake, the selective pressure to keep intact the genes responsible for that pathway might be lowered, because they would not be constantly expressing these biosynthetic genes. Without the selective pressure, the biosynthetic routes might be lost or the gene could allow mutations that would lead to a diversification of the enzyme 's function.

Following this logic, amino acids that are essential for certain organisms might not be essential for other organisms subjected to different selection pressures.

For example, in , Ishikawa and colleagues completed the genome sequence of the endosymbiont bacteria Buchnera , and in it they found the genes for the biosynthetic pathways necessary for the synthesizing essential amino acids for its symbiotic host, the aphid. Interestingly, those genes for the synthesis of its "nonessential" amino acids are almost completely missing Shigenobu et al.

In this way, Buchnera provides the host with some amino acids and obtains the other amino acids from the host Baumann ; Pal et al. Free-living bacteria synthesize tryptophan Trp , which is an essential amino acid for mammals, some plants, and lower eukaryotes.

The Trp synthesis pathway appears to be highly conserved, and the enzymes needed to synthesize tryptophan are widely distributed across the three domains of life. This pathway is one of three that compose aromatic amino acids from chorismate Figure 2, red pathway.

The other amino acids are phenylalanine and tyrosine. Trp biosynthetic enzymes are widely distributed across the three domains of life Xie et al. The genes that code for the enzymes in this pathway likely evolved once, and they did so more recently than those for other amino acid synthesis pathways.

As another point of distinction, the Trp pathway is the most biochemically expensive of the amino acid pathways, and for this reason it is expected to be tightly regulated. To date, scientists have discovered six different biosynthetic pathways in different organisms that synthesize lysine. These pathways can be grouped into the diaminopimelic acid DAP and aminoadipic acid AAA pathways Figure 2, dark blue.

The DAP pathway synthesizes lysine Lys from aspartate and pyruvate. Most bacteria, some archaea , fungi, algae, and plants use the DAP pathways. On the other hand, the AAA pathways synthesize Lys from alpha-ketoglutarate and acetyl coenzyme A.

Most fungi, some algae, and some archaea use this route. Why do we observe this diversity, and why does it occur particularly for Lys synthesis?

Interestingly, the DAP pathways retain duplicated genes from the biosynthesis of arginine, whereas the AAA pathways retain duplicated genes from leucine biosynthesis Figure 2 , indicating that each of the pathways experienced at least one duplication event during evolution Hernandez-Montes et al.

Fani and coworkers performed a comparative analysis of the synthesis enzyme sequences and their phylogenetic distribution that suggested that the synthesis of leucine, lysine, and arginine were initially carried out with the same set of versatile enzymes. Over the course of time came a series of gene duplication events and enzyme specializations that gave rise to the unambiguous pathways we know today.

Which of the pathways appeared earlier is still a source of query and debate. To support this hypothesis, there is evidence from a fascinating archaea, Pyrococcus horikoshii. This organism can synthesize leucine, lysine, and arginine, yet its genome contains only genes for one pathway.

Such a gap indicates that P. horikoshii has a mechanism similar to the ancestral one: versatile enzymes. Biochemical experiments are needed to further support the idea that these enzymes can use multiple substrates and to rule out the possibility that amino acid synthesis in this organism does not arise from enzymes yet unidentified.

Selenocysteine SeC Bock is a genetically encoded amino acid not present in all organisms. Scientists have identified SeC in several archaeal, bacterial, and eukaryotic species even mammals. When present, SeC is usually confined to active sites of proteins involved in reduction-oxidation redox reactions.

It is highly reactive and has catalytic advantages over cysteine, but this high reactivity is undermined by its potential to cause cell damage if free in the cytoplasm.

Hence, it is too dangerous, and no pool of free SeC is available. How, then, is this amino acid synthesized for use in protein synthesis? The answer demonstrates the versatility of synthesis strategies deployed by organisms forced to cope with singularities.

The synthesis of SeC is carried out directly on the tRNA substrate before being used in protein synthesis. First, SeC-specific tRNA tRNA sec is charged with serine via seril-tRNA synthetase, which acts in a somehow promiscuous fashion, serilating either tRNA ser or tRNA sec.

Then, another enzyme modifies Ser to SeC by substituting the OH radical with SeH, using selenophosphate as the selenium donor Figure 2, pink pathway. This synthesis is a form of a trick to avoid the existence of a free pool of SeC while still maintaining a source of SeC-tRNA sec needed for protein synthesis.

Strictly speaking, this mechanism is not an actual synthesis of amino acids, but rather a synthesis of aminoacetylated-tRNAs. However, this technique involving tRNA directly is not exclusive to SeC, and similar mechanisms dependent on tRNA have been described for asparagine, glutamine, and cysteine.

Owing to its appearance of SeC across all three domains of life, scientists wonder if it is an ancestral mechanism for amino acid biosynthesis or simply a coincidence of selection pressures.

In , Horowitz proposed the first accepted model for metabolic pathway evolution Horowitz Called the retrograde model, it states that after an enzyme consumes all its substrate available, another enzyme capable of producing the aforementioned substrate is required, so the last enzyme evolved to the preceding one by a gene duplication and selection mechanism.

In other words, enzymes evolve from others with similar substrate specificity, and the substrate of the last enzyme is the product of the preceding one. Also, the active site must bind both the substrate and the product. This model became very popular, but as more genes have been sequenced and more phylogenetic analyses performed, this mechanism has become less seemingly plausible and therefore unpopular.

An alternative model, the patchwork assembly model, proposes that ancestral enzymes were generalists, so they could bind a number of substrates to carry out the same type of reaction.

Gene duplication events followed by evolutionary divergence would result in enzymes with high affinity and specificity for a substrate.

In other words, enzymes are recruited from others with the same type of chemical reaction. Whole genome analysis of Escherichia coli supports the patchwork evolution model Teichmann et al. Duplication of whole pathways does not occur very often; nevertheless, examples include tryptophan to synthesize paraminobenzoate and histidine to synthesize nucleotides biosynthesis, as well as lysine, arginine, and leucine biosynthesis see aforementioned example.

Amino acids are one of the first organic molecules to appear on Earth. As the building blocks of proteins, amino acids are linked to almost every life process, but they also have key roles as precursor compounds in many physiological processes.

These processes include intermediary metabolism connections between carbohydrates and lipids , signal transduction , and neurotransmission. Recent years have seen great advances in understanding amino acid evolution, yet many questions on the subject of amino acid synthesis remain.

What was the order of appearance of amino acids over evolutionary history? How many amino acids are used in protein synthesis today? How many were present when life began? Were there initially more than twenty used for building blocks, but intense selective process streamlined them down to twenty?

Conversely, was the initial set much less than twenty, and did new amino acids successively emerge over time to fit into the protein synthesis repertoire?

What are the tempo and mode of amino acid pathway evolution? These questions are waiting to be tackled — with old or new hypotheses, conceptual tools, and methodological tools — and are ripe for a new generation of scientists. While the exact mechanism and amino acid balances differ based on the species and type of feed being used, cows, sheep and chickens all exhibited increased production when fed increased amounts of amino acids in their respective diets.

For cattle and sheep specifically, introducing more dietary protein and a better amino acid makeup to cows can increase milk production substantially.

Depending on diet, the limiting amino acids for milk production can be methionine, lysine or any other amino acid. However, research suggests that increasing overall amino acid availability to the small intestine results in an increase in production attributed to the increased availability of disposable non-essential amino acids.

In cows specifically, the delivery of high-quality protein with a well-balanced spread of amino acids was seen to produce a curvilinear increase in milk production 4 , leveling out as the cows reached their genetic limits.

Studies of egg-laying hens found similar results when fed more amino acids. Hens consistently produced more eggs of larger sizes. Unlike cows and sheep, hens do not have a rumen to consider, so unprotected amino acids can be added directly to the diet.

Typically, methionine tends to be the limiting amino acid in the diets of laying hens, and ideally they each should be fed around mg of methionine per day 5 to achieve maximum production.

Lysine and arginine are also highly significant in their diet, though it is equally important for hens to be fed enough pure caloric energy to produce since egg-laying is energetically expensive. During the early phases of growth, all animals need access to as many essential amino acids as possible, as they need to produce sufficient proteins to support their growing bodies.

Studies have shown that an increase in protein intake directly corresponds to an increase in protein deposition 6 within the bodies of growing animals, resulting in stronger, healthier mature animals. Some amino acids are slightly more important than others, however.

Amino Acids for Ruminates: For calves, the most important amino acids are methionine, lysine, isoleucine, threonine and leucine. A deficiency in any of these amino acids results in a slowing of growth and delayed onset of maturity.

The most important of these, methionine, is an essential amino acid. Though used inefficiently from a biological standpoint, methionine is important in cattle and sheep as a methyl group donor and a precursor for cysteine synthesis. Lysine is the second most limiting amino acid for growing calves, especially in maize-based diets because maize is relatively low in lysine.

Amino Acids for Pigs: Pigs have similar needs to calves, with the notable exception being arginine. While arginine is not an essential amino acid since it can be synthesized from glutamate and glutamine, it is essential to younger piglets in the neonatal and immediate postweaning phases.

Forty percent of pigs' arginine requirements 7 must be supplied through their diet, primarily due to their rapid growth rates and the fact that most arginine is used in the urea cycle of the liver. Amino Acids for Poultry: Growing poultry require similar amino acid balances as other growing animals, but they require arginine in their diets because they do not have a urea cycle and therefore cannot synthesize it on their own.

A deficiency of arginine often results in feather deformation in chickens 8. Lysine deficiencies can negatively affect feather growth in turkeys as well. Nutrition has a significant effect on the quality of eggs in all animals.

From the emergence of ovarian follicles through embryonic development, undernutrition can have a devastating effect on reproductive health for farm animals.

By feeding animals sufficient amounts of amino acids to support egg production and embryonic health, you can ensure that your animals are producing healthy offspring at an optimal rate. In ruminants, under-nutrition of amino acids can have a negative effect on fertility, especially during early ovulation.

Most prominently, the intake of methionine and lysine have a strong effect throughout the fertility cycle. These two amino acids are particularly important for embryonic development and consuming too little of either nutrient can negatively impact fertility.

In one study, feeding rumen-protected methionine during the peripartum period of a cow's cycle significantly improved postpartum performance. Additionally, studies have found that pregnancies are healthier when cows are fed sufficient amounts of methionine and lysine through the pregnancy, especially on days nine through 19, during which the cow's body determines whether to continue with a pregnancy.

Pigs require a balanced diet that contains plenty of essential and non-essential amino acids. While essential amino acids are important to support a pregnancy, sows also require dietary glutamine and arginine 9 to support mucosal integrity and neonatal growth, respectively.

In summary, amino acids play varying importance roles based on the species of farm animal, its age and its production purpose. Across all factors, however, protein supplements for cattle, pigs and poultry can deliver promising results and improve the performance and profitability of an animal.

Here are just a few ways that essential amino acids for animal health can benefit your bottom line:. When you raise the protein level in farm animal feed, farm animals will eat more food and digest it more efficiently, in turn increasing the amounts of amino acids and nutrients available to the animal.

This also improves feed efficiency, so there is less waste. Appropriate amino acid balances support improved growth rate so that animals will wean and reach mature weight early. Additionally, well-fed calves, piglets and chicks tend to be healthier and larger as adults, producing more and experiencing disease at a lower rate.

The most prominent reason for culling cows is reproduction — if a cow doesn't calve, it doesn't produce milk. Conversely, the higher an animal's production potential, the higher the value of the pregnancy.

By increasing the amount and the quality of amino acids in feed, especially methionine and lysine, studies have shown an improvement in pregnancy rates 10 , which not only contribute to herd numbers but also improve milk production, increasing profitability.

Regardless of how much a cow is producing, it costs the same to keep it in the herd due to operating costs, fixed overhead costs, maintenance requirements and dry matter. To make the most of that cow, it is important that she produces enough milk to offset any costs of increasing feed quality.

By improving the ratio of amino acids in the diet, you can increase cow's milk production cost-effectively and achieve a positive return on investment. Higher incidence of disease leads to diminished production and higher maintenance costs, reducing the profitability of your farm.

Additionally, a disease can impact the future production potential of a segment of your herd, negatively affecting production in the long-term.

Are you interested in learning more about amino acid products and how they can help you achieve more with your livestock? Learn about the products that might be best for you, as well as their benefits and potential for improving your animals' performance and profitability. Learn about your options 11 or contact us with questions about our products today.

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