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Amino Acids : Biochemistry And Nutrition !FULL!

Following its predecessor, the second edition of Amino Acids: Biochemistry and Nutrition presents exhaustive coverage of amino acids in the nutrition, metabolism and health of humans and other animals. Substantially revised, expanded and updated to reflect scientific advances, this book introduces the basic principles of amino acid biochemistry and nutrition, while highlighting the current knowledge of the field and its future possibilities.

Amino acids : biochemistry and nutrition


The book begins with the basic chemical concepts of amnio acids, peptides and proteins, and their digestion and absorption. Subsequent chapters cover cell-, tissue-, and species-specific synthesis and catabolism of amino acids and related bioactive metabolites, and the use of isotopes to study amino acids metabolism in cells and the body. The book details protein turnover, physiological functions of amino acids, as well as both the regulation and inborn errors of amino acid metabolism. The book concludes with a presentation on human and animal dietary requirements of amino acids and evaluates dietary protein quality.

The recent years have witnessed growing interest in biochemistry, physiology and nutrition of amino acids (AA) in growth, health and disease of humans and other animals. This results from the discoveries of AA in cell signaling involving protein kinases, G protein-coupled receptors, and gaseous molecules (i.e., NO, CO and H2S). In addition, nutritional studies have shown that dietary supplementation with several AA (e.g., arginine, glutamine, glutamate, leucine, and proline) modulates gene expression, enhances growth of the small intestine and skeletal muscle, or reduces excessive body fat. These seminal findings led to 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. Functional AA hold great promise in prevention and treatment of metabolic diseases (e.g., obesity, diabetes, and cardiovascular disorders), intrauterine growth restriction, infertility, intestinal and neurological dysfunction, and infectious disease (including viral infections).

Essential amino acids, also known as indispensable amino acids, are amino acids that humans and other vertebrates cannot synthesize from metabolic intermediates. These amino acids must be supplied from an exogenous diet because the human body lacks the metabolic pathways required to synthesize these amino acids. In nutrition, amino acids are classified as either essential or non-essential. These classifications resulted from early studies on human nutrition, which showed that specific amino acids were required for growth or nitrogen balance even when there is an adequate amount of alternative amino acids. Although variations are possible depending on the metabolic state of an individual, the general held thought is that there are nine essential amino acids, including phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, leucine, and lysine. The mnemonic PVT TIM HaLL ("private Tim Hall") is a commonly used device to remember these amino acids as it includes the first letter of all the essential amino acids. In terms of nutrition, the nine essential amino acids are obtainable by a single complete protein. A complete protein, by definition, contains all the essential amino acids. Complete proteins usually derive from animal-based sources of nutrition, except for soy. The essential amino acids are also available from incomplete proteins, which are usually plant-based foods. The term "limiting amino acid" is used to describe the essential amino acid present in the lowest quantity in a food protein relative to a reference food protein like egg whites. The term "limiting amino acid" may also refer to an essential amino acid that does not meet the minimal requirements for humans.

Nonessential means that our bodies can produce the amino acid, even if we do not get it from the food we eat. Nonessential amino acids include: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

You do not need to eat essential and nonessential amino acids at every meal, but getting a balance of them over the whole day is important. A diet based on a single plant item will not be adequate, but we no longer worry about pairing proteins (such as beans with rice) at a single meal. Instead we look at the adequacy of the diet overall throughout the day.

Trumbo P, Schlicker S, Yates AA, Poos M; Food and Nutrition Board of the Institute of Medicine, The National Academies. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein and amino acids. J Am Diet Assoc. 2002;102(11):1621-1630. PMID: 12449285

Amino acids are the building blocks of protein. Proteins are long chains of amino acids. Your body has thousands of different proteins that each have important jobs. Each protein has its own sequence of amino acids. The sequence makes the protein take different shapes and have different functions in your body.

Your body produces the rest of the 11 amino acids you need. These are called nonessential amino acids. The nonessential amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.

Essential amino acids can be found in many different foods. The best sources of amino acids are found in animal proteins such as beef, poultry and eggs. Animal proteins are the most easily absorbed and used by your body.

You can usually get all the essential amino acids your body needs by eating a healthy, balanced diet. Some people take amino acid supplements to get better sleep, improve their mood and enhance athletic performance. But the U.S. Food and Drug Administration (FDA) has not approved these supplements. You should speak with your healthcare provider before starting any supplements, including amino acid supplements.

Additionally, certain amino acids, including glycine and arginine, are considered conditionally essential during pregnancy because a pregnant person needs more of these amino acids to support their own health and the health of the fetus (5, 6).

A study in 243 people with pelvis or long bone fractures found that those who took conditionally essential amino acids for 2 weeks after surgery had lower rates of death and medical complications than those who received standard nutrition (25).

Proteins are complex, organic compounds composed of many amino acids linked together through peptide bonds and cross-linked between chains by sulfhydryl bonds, hydrogen bonds and van der Waals forces. There is a greater diversity of chemical composition in proteins than in any other group of biologically active compounds. The proteins in the various animal and plant cells confer on these tissues their biological specificity.1.1 ClassificationProteins can be classified as:(a) Simple proteins. On hydrolysis they yield only the amino acids and occasional small carbohydrate compounds. Examples are: albumins, globulins, glutelins, albuminoids, histones and protamines. (b) Conjugated proteins. These are simple proteins combined with some non-protein material in the body. Examples are: nucleoproteins, glycoproteins, phosphoproteins, haemoglobins and lecithoproteins. (c) Derived proteins. These are proteins derived from simple or conjugated proteins by physical or chemical means. Examples are: denatured proteins and peptides.1.2 StructureThe potential configuration of protein molecules is so complex that many types of protein molecules can be constructed and are found in biological materials with different physical characteristics. Globular proteins are found in blood and tissue fluids in amorphous globular form with very thin or non-existent membranes. Collagenous proteins are found in connective tissue such as skin or cell membranes. Fibrous proteins are found in hair, muscle and connective tissue. Crystalline proteins are exemplified by the lens of the eye and similar tissues. Enzymes are proteins with specific chemical functions and mediate most of the physiological processes of life. Several small polypeptides act as hormones in tissue systems controlling different chemical or physiological processes. Muscle protein is made of several forms of polypeptides that allow muscular contraction and relaxation for physical movement.1.3 PropertiesProteins can also be characterized by their chemical reactions. Most proteins are soluble in water, in alcohol, in dilute base or in various concentrations of salt solutions. Proteins have the characteristic coiled structure which is determined by the sequence of amino acids in the primary polypeptide chain and the stereo configuration of the radical groups attached to the alpha carbon of each amino acid. Proteins are heat labile exhibiting various degrees of lability depending upon type of protein, solution and temperature profile. Proteins can be reversible or irreversible, denatured by heating, by salt concentration, by freezing, by ultrasonic stress or by aging. Proteins undergo characteristic bonding with other proteins in the so-called plastein reaction and will combine with free aldyhyde and hydroxy groups of carbohydrates to form Maillard type compounds.1.4 Chemical DeterminationThe nitrogen content of most proteins found in animal, nut and grain tissue is about 16 percent; therefore, protein content is commonly expressed as nitrogen content 6.25.2. PROTEIN DIGESTION AND METABOLISMIngested proteins are first split into smaller fragments by pepsin in the stomach or by trypsin or chymotrypsin from the pancreas. These peptides are then further reduced by the action of carboxypeptidase which hydrolyzes off one amino acid at a time beginning at the free carboxyl end of the molecule or by aminopeptidase which splits off one amino acid at a time beginning at the free amino end of the polypeptide chain. The free amino acids released into the digestive system are then absorbed through the walls of the gastro intestinal tract into the blood stream where they are then resynthesized into new tissue proteins or are catabolyzed for energy or for fragments for further tissue metabolism.3. GROSS PROTEIN REQUIREMENTSGross protein requirements have been determined for a few species of fish (see Table 1). Simulated whole egg protein component of test diets contains an excess of indispensable amino acids. These diets were kept approximately isocaloric by adjusting total protein plus digestible carbohydrate components to a fixed amount as the protein diet treatments were varied over the ranges tested. Tests in feeding fry, fingerling, and yearling fish have shown that gross protein requirements are highest in initial feeding fry and that they decrease as fish size increases. To grow at the maximum rate, fry must have a diet in which nearly half of the digestible ingredients consist of balanced protein; at 6-8 weeks this requirement is decreased to about 40 percent of the diet for salmon and trout and to about 35 percent of the diet for yearling salmonids raised at standard environmental temperature (SET). See Figures 1 and 2. Gross protein requirements for young Catfish appear to be less than those for salmonids. Initially feeding fry require that about 50 percent of the digestible components of the ration be protein, and the requirement decreases with size. Some feeding trials with salmon have indicated direct relationships between changes in the protein requirements of young fish and changes in water temperature. Chinook salmon in 7 C water require about 40 percent whole egg protein for maximum growth; the same fish in 15 C water require about 50 percent protein. Salmon, trout and catfish can use more protein than required for maximum growth because of efficiency in eliminating nitrogenous wastes in the form of soluble ammonia compounds through the gill tissue directly into the water environment. This system for eliminating nitrogen is more efficient than that available to fowl and mammals. Fowl and mammals consume energy to synthesize urea, uric acid, or other nitrogen compounds which are excreted through the kidney tissue and expelled in urine. Digestible carbohydrate and fat will spare excess protein in the diet as long as the protein requirement for maximum growth is met (Figures 1 and 2).Table 1 - Estimated Dietary Protein Requirement of Certain Fish 1/SpeciesCrude protein level in diet for optimal growth (g/kg)Rainbow trout (Salmo gairdneri)400-460Carp (Cyprinus carpio)380Chinook salmon (Oncorhynchus tshawytscha)400Eel (Anguilla japonica)445Plaice (Pleuronectes platessa)500Gilthead bream (Chrysophrys aurata)400Grass carp (Ctenopharyngodon idella)410-430Brycon sp.356Red sea bream (Chrysophrys major)550Yellowtail (Seriola quinqueradiata)5501/Adapted from C.B. Cowey, 1978Fig. 1. Protein requirement of chinook salmon at 47F. Top curve: initial individual average weight of fish, 1.5g. Bottom curve: initial individual average weight of fish, 5.6g.Fig. 2. Protein requirement of chinook salmon at 58F. Top curve: initial individual average weight of fish, 2.6g. Bottom curve: initial individual average weight of fish, 5.8g. (Both figures adapted from: DeLong, D.C., J.E. Halver and E.T. Mertz, 1958, J.Nutr., 65:589-99)Basically the fish must be given a diet containing graded levels of high quality protein and energy and adequate balances of essential fatty acids, vitamins and minerals over a prolonged period. From the resulting dose/response curve the protein requirement is usually obtained by an Almquist plot. These differences in apparent protein requirement are thought to be due to differences in culture techniques and diet composition.The relatively high dietary protein levels required for maximal growth of certain fish such as grass carp, Ctenopharyngodon idella, and Brycon spp. are surprising as these fish are omnivorous. Brycon spp. are grown on unwanted fruit and other plant material of low protein content and under these conditions there is presumably a substantial contribution to their protein intake from a natural food chain.Protein requirement of eurythaline fish such as the rainbow trout, Salmo gairdneri, and the coho salmon, Oncorhynchus kisutch, reared in water of salinity 20 ppt is about the same as the requirement in freshwater. No data are available for the protein requirement of these species in full strength sea water.(35 ppt).4. AMINO ACIDS 4.1 Essential and Non-essential Amino Acids 4.2 Essential Amino Acids and Protein Quality 041b061a72


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