Valine essential amino acid

Humans have a limited capacity to synthesize amino acids de novo, but extensive interconversions can occur. Those amino acids which cannot be formed within the body and must be supplied by the diet are called essential . Members of this group, which includes the branched chain amino acids leucine and valine, and also methionine and phenylalanine, are all dietary requirements. Such essential amino acids may be chemically converted, mainly in the liver, into the non-essential amino acids. The term non-essential does not equate with not biochemically important but simply means they are not strict dietary components. 

Because of their unique biological functions, a significant and growing part of new drug discovery and development is focused on this class of biomolecules. Their biological functions are determined by the exact arrangement, or sequence of different amino acids in their makeup. There are 20 naturally occurring amino acids, 8 of which are essential amino acids, namely, l-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-valine, l-threonine, and L-tryptophan. 

Kirchgessner and Steinhart (52) studied the in vitro digestion of soy protein isolate with pepsin. They showed that a relatively higher percentage of the essential amino acids threonine, valine, isoleucine, leucine and phenylalanine were found in the undigested residue and therefore would be present in lower proportions in the hydrolysate. Myers et al. ( ) hydrolyzed a soy protein isolate with a fungal acid protease. They also found that the essential amino acid content of the hydrolyzate was lower than the isolate, but, as prepared by their continuous process, the hydrolyzate PER was not significantly reduced as compared to the isolate PER. 

Methionine, threonine, lysine, isoleucine, valine, and leucine are essential amino acids. Their biosynthetic pathways are complex and interconnected (Fig. 22-15). 

FIGURE 22-15 Biosynthesis of six essential amino acids from oxalo-acetate and pyruvate in bacteria methionine, threonine, lysine, isoleucine, valine, and leucine. Here, and in other multistep pathways, the enzymes are listed in the key. Note that L,L-a,e-diaminopimelate, the product of step (HI), is symmetric. The carbons derived from pyruvate (and the amino group derived from glutamate) are not traced beyond this point, because subsequent reactions may place them at either end of the lysine molecule. 

The branched-chain amino acids, isoleucine, leucine, and valine, are essential amino acids. In contrast to other amino acids, they are metabolized primarily by the peripheral tissues (particularly muscle), rather than by the liver. Because these three amino acids have a similar route of catabolism, it is convenient to describe them as a group (see Figure 20.10). 

In a rare autosomal recessive condition (discovered in 1954) the urine and perspiration has a maple syrup odor/ High concentrations of the branched-chain 2-oxoacids formed by transamination of valine, leucine, and isoleucine are present, and the odor arises from decomposition products of these acids. The branched-chain amino acids as well as the related alcohols also accumulate in the blood and are found in the urine. The biochemical defect lies in the enzyme catalyzing oxidative decarboxylation of the oxoacids, as is indicated in Fig. 24-18. Insertions, deletions, and substitutions may be present in any of the subunits (Figs. 15-14,15-15). The disease which may affect one person in 200,000, is usually fatal in early childhood if untreated. Children suffer seizures, mental retardation, and coma. They may survive on a low-protein (gelatin) diet supplemented with essential amino acids, but treatment is difficult and a sudden relapse is apt to prove fatal. Some patients respond to administration of thiamin at 20 times the normal daily requirement. The branched-chain oxoacid dehydrogenase from some of these children shows a reduced affinity for the essential coenzyme thiamin diphosphate.d... 

Proteins are either complete or incomplete. Complete protein simply means that it contains at least the minimal amounts of amino acids to sustain life. Which of course under lines the fact that a high protein "content" does not necessarily mean a high quality protein. It is the essential amino acid pattern and ratio that counts most. The essential amino acids are L-Leucine, L-Isoleucine, L-Valine, (These three are branch chain amino... 

Human beings are able to synthesize 10 of the amino acids, termed nonessentiul amino acids, from other compounds in the diet. However, the other 10 amino acids, termed essential amino acids, cannot be synthesized by humans (or are synthesized only in small amounts) and must be obtained from protein sources in the diet. The essential amino acids are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. 

A minor pathway of valine catabolism is concerned with its conversion to leucine. Because leucine is an essential amino acid, its synthesis from valine is clearly not sufficiently significant to meet the organism s daily demand for leucine. In this reaction, isobutyryl-CoA (see Figure 20.20) is condensed with a molecule of acetyl-CoA to give /3-ketoisocaproate, which is then transaminated to give (3-leucine. A mutase is then used to convert /3-leucine to leucine. This mutase... 

Tribenuronmethyl (Sulfonyl urea) CO.CH, OCH, n C >-SOjNHCON—< N CH- CHj Branched chain amino acid synthesis (ALS and A HAS) inhibitor. Acts by inhibiting biosynthesis of the essential amino acids valine and isoleucine, hence stopping cell division and plant growth... 

In vertebrates, the major sources of propionate and methylmalonate are odd chain fatty acids and the amino acids isoleucine, valine and methionine (8,9). In the termite Zootermopsls angusticollls. which can incorporate propionate as the methyl branch unit of mono- and dimethylalkanes (7), these sources were considered unlikely because the diet of termites presumably contains little fatty acid and Z. angusticollls contains very small amounts of odd chain length fatty acids (Chu and Blomqulst, unpublished). Likewise, termites would be expected to conserve essential amino acids such as the ones that could serve as precursors to propionate and methylmalonate. 

The liver plays a central role in the synthesis of nearly all circulating proteins. Plasma contains 60-80 g/L of protein and this is turned over at a rate of approximately 250 g/day. A variety of proteins are constructed in the liver using amino acids (Aa) as their basic building blocks. Amino acids are categorised as essential and non-essential , the former being a requirement of dietary intake as they cannot be constructed in vivo, whereas the latter can be synthesised hepatically. The essential amino acids are further categorised as branched-chain amino acids (BCAA leucine, valine, isoleucine) or aromatic amino acids (AAA phenylalanine, tyrosine, methionine) according to their structure. Table... 

Oxo-isovalerate may be formed by the transamination of valine it is also the immediate precursor of valine biosynthesis and an intermediate in the synthesis of leucine (both are essential amino acids in mammals). Oxo-lso-valerate undergoes a hydroxymethyl transfer reaction, in which the donor is... 

On the other hand, other studies focused on O. oeni amino acid requirements for growth and malolactic fermentation in several growth media (Tracey and Britz 1989). Remize et al. (2006) determined the essential amino acids for the growth of five different strains of Oenococcus oeni. These amino acids corresponded to glutamic acid, methionine, phenylalanine, serine and tyrosine for all the strains studied. They also found that the amino acids valine, leucine, tryptophan, isoleucine, histidine and arginine were essential or necessary for the strains studied, but that the amino acids alanine, glycine and proline were not essential. 

Although all of the amino acids listed in Table SO-1 are present in the proteins of the human body, not all of them need to be in the food. Experiments have been carried out which show that nine of the amino acids are essential to man. 1 hese nine essential amino acids are histidine, lysine, tryptophan, phenylalanine, leucine, isoleucine, threonine, methionine, and valine. The human body seems to be able to manufacture the others, which are called the non-essential amino acids. Some organisms that we usually consider to be simpler than man have greater powers than the human organism, in that they are able to manufacture all of the amino acids from inorganic constituents. The red bread mold, Neurospora, has this power. 

Most of the prokaryotic and many eukaryotic organisms (plants) are capable of synthesizing all the amino acids present in the protein. But higher animals including man possess this ability only for certain amino acids. The other amino acids, which are needed for normal functioning of the body but cannot be synthesized from metabolic intermediates, are called essential amino acids. These must be obtained from the diet and a deficiency in any one of the amino acids prevents growth and may even cause death. Methionine, Threonine, Tryptophan, Valine, Isoleucine, Leucine, Phenylalanine and Lysine are the essential amino acids, however, Histidine and Arginine are considered semi essential amino acids as it can be partly synthesized by the body. 

Nine amino acids cannot be synthesized in the body and, therefore, must be present in the diet in order for protein synthesis to occur. The essential amino acids are lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, methionine, and histidine. 

D. Valine is an essential amino acid and is not synthesized in the human. Glydne reacts with sucdnyl CoA in the first step of heme synthesis and with arginine in the first step of creatine synthesis. The entire glycine molecule is incorporated into the growing purine ring. 

Propionyl-CoA is an intermediary product in the metabo-hsm of four essential amino acids (isoleucine, valine, threonine, and methionine), the aliphatic side-chain of cholesterol, pyrimidines (uracd and thymine), and the final product of the [3-oxidation of odd-chain fatty acids. Under normal circumstances, propionyl-CoA first is converted by a biotin-dependent carboxylase to methylmalonyi-CoA, then to succinyl-CoA by an adenosylcobalamin-dependent mutase, leading to oxidation in the tricarboxylic acid cycle. Primary or secondary defects of these two enzymes were among the first organic acidurias to be discovered, and their natural history has been characterized perhaps better than any other inborn error of organic acid metabolism. 

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