Amino Acids Metabolism Functions And Nutrition Pdf

amino acids metabolism functions and nutrition pdf

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Recent years have witnessed the discovery that amino acids AA are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. Additionally, AA are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance.

Branch chain amino acids BCAAs have unique properties with diverse physiological and metabolic roles. They have functions other than simple nutrition. Different diseases including metabolic disease lead to protein loss, especially muscle protein.

Amino acids: metabolism, functions, and nutrition

Amino acids AA were traditionally classified as nutritionally essential or nonessential for animals and humans based on nitrogen balance or growth. A key element of this classification is that all nonessential AA NEAA were assumed to be synthesized adequately in the body as substrates to meet the needs for protein synthesis.

Unfortunately, regulatory roles for AA in nutrition and metabolism have long been ignored. Such conceptual limitations were not recognized until recent seminal findings that dietary glutamine is necessary for intestinal mucosal integrity and dietary arginine is required for maximum neonatal growth and embryonic survival. Some of the traditionally classified NEAA e.

Additionally, glutamate, glutamine, and aspartate are major metabolic fuels for the small intestine and they, along with glycine, regulate neurological function. Among essential AA EAA , much emphasis has been placed on leucine which activates mammalian target of rapamycin to stimulate protein synthesis and inhibit proteolysis and tryptophan which modulates neurological and immunological functions through multiple metabolites, including serotonin and melatonin. A growing body of literature leads to a new concept of functional AA, which are defined as those AA that regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of organisms.

Based on growth or nitrogen balance namely net synthesis of protein in the whole body , amino acids AA 3 have traditionally been classified as nutritionally essential indispensable or nonessential dispensable for animals and humans 1 , 2. Nutritionally essential AA EAA are those whose carbon skeletons are not synthesized by animal cells and, therefore, must be provided from the diet.

Dietary essentiality of some AA e. It was tactically assumed, without much evidence, that animals or humans could synthesize sufficient amounts of all NEAA and did not need them in diets for optimal nutrition or health. However, growing evidence from cell culture and animal studies shows that some of the traditionally classified NEAA e. Clearly, cell- and tissue-specific functions of AA beyond protein synthesis Fig.

Roles of AA in nutrition and whole-body homeostasis. Besides serving as building blocks for proteins, AA have multiple regulatory functions in cells. These nutrients are crucial for growth, development, and health of animals and humans. A growing body of literature has led to the development of the concept of functional AA FAA , which are defined as those AA that regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of organisms 2.

Notably, supplementing a specific FAA e. In view of the foregoing, the major objective of this article is to highlight recent advances in understanding the roles for FAA in nutrient metabolism, growth, reproduction, and health. Milk has traditionally been thought to provide adequate amounts of all AA to neonates.

Besides arginine, the amount of milk-borne proline that enters the portal vein is inadequate to support proline requirements for protein synthesis in the piglet Thus, a 7-d-old pig must synthesize daily at least 0.

Based on a degradation rate [0. Considering the extensive utilization of arterial glutamine by enterocytes and other cell types including kidneys and lymphocytes 15 , dietary glutamine is also substantially inadequate for protein synthesis in extra-intestinal tissues of piglets and the rate of de novo synthesis of glutamine is likely very high in the suckling piglet [at least 0. Similarly, a typical corn- and soybean meal-based diet cannot provide sufficient amounts of arginine, proline, aspartate, glutamate, glutamine, or glycine for protein accretion in postweaning growing pigs Table 1.

Use of dietary AA for protein accretion in sow-reared d-old pigs and d-old pigs weaned at 21 d of age 1. Adapted from Wu et al. Arginine and proline are EAA for young pigs because of inadequate synthesis 4. Values for AA accretion are percent.

Values in parentheses are percent of AA entering the portal vein from the small intestine. Pathways for the synthesis of arginine, glutamine, glutamate, and proline and alanine are now well documented and have important nutritional and physiological significance 2 , 3 , In contrast, little is known about how glycine is produced in the body. Currently, the underlying pathways including substrates and reactions for glycine synthesis are largely unknown. These pathways are expected to be nutritionally and physiologically important, because high rates of glycine utilization support the synthesis of protein, creatine, N 5 -N 10 -methylene-tetrahydrofolate, nucleotides, and other nitrogenous products 2 , Dietary intake of most EAA exceeds their use for protein synthesis in the body.

In contrast, the typical corn- and soybean meal-based diet cannot provide sufficient amounts of arginine, aspartate, glutamate, glutamine, glycine, and proline for protein accretion for young pigs, and these AA must be synthesized from EAA.

It had been a long-standing belief that after digestion, dietary AA absorbed by enterocytes entered the portal vein intact. Among dietary AA, the rate of degradation in the small intestine is the greatest for glutamate, followed by glutamine, aspartate, and proline. Of particular note, the small intestine takes up a large amount of glutamine, but no glutamate or aspartate, from the arterial blood. Consequently, the total rate of utilization of glutamine by the gut may be greater than that for glutamate.

Nitrogenous products of glutamate and glutamine include ornithine, citrulline, arginine, proline, aspartate, and alanine 2. Despite much work on glutamate oxidation in the gut, little is known about the effects of dietary glutamate supplementation on intestinal mucosal integrity and function, particularly under stressful conditions.

Intestinal metabolism of AA has profound impacts on nutrition and health. First, catabolism of glutamine, glutamate, and aspartate provides most of the ATP to maintain gut integrity and function 3.

Second, because elevated levels of glutamine, glutamate, and aspartate in plasma exert a neurotoxic effect 2 , their extensive catabolism by the small intestine is essential to the survival of organisms. Thus, the ratios of most AA in diets relative to lysine differ markedly from those entering the portal vein from the small intestinal lumen or appearing in plasma and body proteins The discrepancies in the patterns of AA between diets and body proteins are particularly large for arginine, histidine, methionine, proline, glutamine, glycine, and serine Therefore, ratios of these AA to lysine in body proteins are not accurate estimates of their optimal dietary requirements by rapidly growing animals or infants.

This conceptual limitation also applies to gestating and lactating dams. Two of the most studied AA regarding regulation of gene expression are glutamine and arginine. These findings provide molecular mechanisms for the beneficial effects of dietary glutamine supplementation to improve nutritional status in young mammals.

In the adult-rat WAT, there is no synthesis of fatty acids due to the lack of acetyl-CoA carboxylase, but arginine enhances lipolysis in this tissue 23 — Biochemical analysis has revealed that oxidative stress in the obese-rat WAT can be prevented by arginine supplementation Also, upregulation of genes involved in mitochondrial biogenesis by arginine provides another mechanism for increased oxidation of long-chain fatty acids and glucose in insulin-sensitive tissues Upon acetylation of histones, DNA is dissociated from histones so that transcription will proceed.

In contrast, DNA methylation and histone deacetylation result in highly dense packing of DNA and, therefore, silence gene expression. This process can be regulated by AA through 1 or more of the following mechanisms: 1 alteration of specificity of RNA polymerase for promoters; 2 binding of repressors to noncoding DNA sequences that are near or overlap the promoter region; and 3 transcription factors e.

Covalent modifications of DNA and core histones provide a basis for epigenetics stable alterations in gene expression without changes in the underlying DNA sequence 26 , Epigenetic changes may remain through cell divisions and, therefore, may be carried forward to subsequent generations This notion of transgenerational effects of AA has important implications for human health and animal production. Initiation of mRNA translation is a key event in the regulation of protein synthesis.

Activation of mTOR may also result in inhibition of intracellular protein degradation, possibly via mechanisms involving autophagy and other unknown pathways 2 , Inadequate content of arginine and glutamine as well as other NEAA in a low-protein There are suggestions that some AA may directly act to phosphorylate mTOR or its down-stream target proteins 25 , Evidence also exists that certain AA may indirectly do so via the production of their metabolites 35 or interaction with Rag GTPases for binding raptor Although results from cell culture studies led to 3 models to explain how AA can regulate protein synthesis in cells Fig.

This is because in vitro experiments were conducted under conditions of either complete absence of an AA or its presence at a particularly high concentration e.

Nonetheless, the potential for FAA either EAA or NEAA to stimulate protein synthesis indicates that these nutrients play important regulatory roles beyond serving as building blocks of proteins. Models for regulatory roles of AA in protein synthesis. All of these changes stimulate the initiation of protein synthesis in cells. Some AA e. In addition, high-protein intake, arginine, glutamine, glutamate, alanine, taurine, methionine, and glycine promote CO synthesis by heme oxygenase in endothelial cells and nonvascular tissues, but N-acetyl-cysteine attenuates CO formation in injured brain and vascular smooth muscle cells Furthermore, H 2 S production is stimulated by high-protein intake, arginine, cysteine, methionine, glycine, S -adenosylmethionine, N-acetyl-glutamate, and glutamate 0.

Either imbalance or antagonism among AA affects the generation of 1 or more of these gaseous molecules and, therefore, protein nutrition in organisms. NO is a highly reactive free radical They are all water-soluble, colorless molecules that easily penetrate biological membranes. Therefore, these gases exert their effects on cells independent of membrane receptors. At pathological levels, they are extremely destructive to all cell types 40 , At physiological levels, NO, CO, and SO 2 activate guanylyl cyclase to generate cGMP, which elicits a variety of responses via cGMP-dependent protein kinases that include relaxation of vascular smooth muscle cells, hemodynamics, neurotransmission, and cell metabolism 40 , The actions of these gases may also involve cGMP-independent mechanisms e.

Emerging evidence shows that H 2 S is a crucial regulator of both neurological function and endothelium-dependent relaxation through cGMP-independent mechanisms involving stimulation of membrane K ATP channels and intracellular cAMP signaling AA are essential precursors for the synthesis of a wide array of nitrogenous substances with enormous biological importance 2.

Some of these bioactive molecules include neurotransmitters e. Metabolism of AA is altered under various physiological and pathological conditions, leading to changes in whole-body homeostasis 14 , 16 , 44 , Historically, our understanding of human protein nutrition has been based largely on animal studies 1 — 3.

The relative growth rates percent change per day and food intake percent of body weight of rodents, pigs, and poultry are higher than those for humans and primates 46 — Because the composition of AA in the body is similar among species 2 , requirements of intracellular AA e.

Thus, new knowledge gained from animal models has important implications for human nutrition. First, as reported for sow-reared piglets 8 , provision of arginine from human or primate milk is inadequate for optimal protein accretion in breast-fed infants This necessitates endogenous synthesis of arginine from glutamate, glutamine, and proline in infants 4. Second, dietary supplementation with arginine prevents necrotizing enterocolitis the most common and severe intestinal disease in preterm infants 47 , who have underdeveloped arginine-synthetic enzymes and insufficient arginine intake Similarly, arginine ameliorates intestinal damage in early-weaned piglets with naturally-occurring gut atrophy Third, a deficiency of dietary glutamine impairs cell signaling and results in intestinal atrophy in both piglets and infants Nonetheless, new knowledge about AA biochemistry and physiology has resulted in fruitful translational research to improve human and animal health, as well as animal production.

For example, supplementation with AA e. Studies with pigs, sheep, and rats have also demonstrated that glutamine and arginine enhance the survival, growth, and development of the embryo, fetus, and neonate 4 , 14 as well as intestinal restitution, integrity, and function Additionally, arginine ameliorates obesity, hyperglycemia, dyslipidemia, hypertension, cardiovascular dysfunction, and other problems of metabolic syndrome in humans and animals while enhancing milk production, mitochondrial biogenesis, growth of brown adipose tissue, wound healing, muscular strength and glycolysis, and spermatogenesis 4 , 9 , 14 , Meat quality can also be improved through supplementing arginine to growing-finishing pigs before slaughter 53 ,

Essential Amino Acids: Definition, Benefits and Food Sources

Protein metabolism denotes the various biochemical processes responsible for the synthesis of proteins and amino acids anabolism , and the breakdown of proteins by catabolism. The steps of protein synthesis include transcription, translation, and post translational modifications. This mRNA sequence contains codons: 3 nucleotide long segments that code for a specific amino acid. Ribosomes translate the codons to their respective amino acids. The amino acids are joined by peptide bonds making a polypeptide chain. This polypeptide chain then goes through post translational modifications and is sometimes joined with other polypeptide chains to form a fully functional protein.

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Amino acids, often referred to as the building blocks of proteins, are compounds that play many critical roles in your body. Some may also be taken in supplement form for a natural way to boost athletic performance or improve mood. This article tells you everything you need to know about essential amino acids, including how they function, possible food sources and the benefits of taking a supplement. Amino acids are organic compounds composed of nitrogen, carbon, hydrogen and oxygen, along with a variable side chain group. Your body needs 20 different amino acids to grow and function properly.

Recent years have witnessed the discovery that amino acids AA are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. Additionally, AA are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance. Physiological concentrations of AA and their metabolites e.

Amino acids AA were traditionally classified as nutritionally essential or nonessential for animals and humans based on nitrogen balance or growth. A key element of this classification is that all nonessential AA NEAA were assumed to be synthesized adequately in the body as substrates to meet the needs for protein synthesis. Unfortunately, regulatory roles for AA in nutrition and metabolism have long been ignored. Such conceptual limitations were not recognized until recent seminal findings that dietary glutamine is necessary for intestinal mucosal integrity and dietary arginine is required for maximum neonatal growth and embryonic survival.

Metabolic and Physiological Roles of Branched-Chain Amino Acids

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Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: AbstractRecent years have witnessed the discovery that amino acids AA are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. Additionally, AA are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance. Physiological concentrations of AA and their metabolites e. View on Springer.

Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. How protein got its name is an interesting story Hartley, The traditional credit for coining the word "protein" goes to the Dutch chemist Gerardus Johannes Mulder, who in an article published in the Bulletin des Sciences Physiques et Naturelles en Neerlande on July 30, , stated in French that this material was the essential general principle of all of the constituents of the animal body and defined it by the Greek word "proteus," which he translated in Latin to "primarius," that is, the primary constituent of the body Hartley, The interesting part of the story is that Mulder appears to have taken the term directly from Swedish chemist Sac Berzelius, who, on July 10, sent Mulder a letter in which Berzelius suggested the name "protein. Dennis M. Besides the apparent use of the new term without proper attribution was the situation of a Dutch chemist, writing in a Dutch journal, defining a new word in French that was derived from Greek, and then qualifying its meaning in Latin!


Regulatory roles of AA · Gene expression · Synthesis and secretion of hormones · Nutrient metabolism and oxidative defense · Intracellular protein.


Refworks Account Login. UBC Theses and Dissertations. Featured Collection. It has been suggested that some NEAA may be more metabolically important than others.

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Recent years have witnessed the discovery that amino acids (AA) are not only cell signaling molecules but are also regulators of gene expression and the.

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