Muscle valine

Valine A branched-chain essential amino add that has stimulant activity. It promotes muscle growth and tissue repair. It is a precursor in the penicillin biosynthetic pathway. [NIH]... 

In a muscle at rest, most of the 2-oxo acids produced from transamination of branched chain amino acids are transported to the liver and become subject to oxidation in reactions catalysed by branched-chain 2-oxo acid dehydrogenase complex. During periods of exercise, however, the skeletal muscle itself is able to utilize the oxo-acids by conversion into either acetyl-CoA (leucine and isoleucine) or succinyl-CoA (valine and isoleucine). 

Valine (Val or V) ((5)-2-amino-3-methyl-butanoic acid) is a nonpolar, neutral, aliphatic amino acid with the formula HOOCCH(NH2)CH(CH3)2. Along with Leu and He, Val is a branched-chain amino acid and is found in high concentrations in the muscles. Val is needed for muscle metabolism and coordination, tissue repair, and for the maintenance of proper nitrogen balance in the body. ° The steric hindrance present in Val and He (caused by branching) lowers the rate of coupling reactions, resulting in an increase in side reactions. ... 

In muscle, the concentrations of alanine, aspartate, glutamate, glutamine, leucine, serine and valine are high that of glutamine is the highest (c. 20mmol/L). The lowest are those of methionine, tryptophan and tyrosine. 

Branched-chain amino acids are leucine, isoleucine and valine the increased concentrations are also consistent with an increased rate of degradation, as muscle protein contains a high proportion of these amino acids. The extent of the decrease in ATP concentration is even greater than in exaustive physical activity. Note the very large fall is glutamine concentration. 

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). 

Haem is bound to proteins to make haemoglobin (in blood) and myoglobin (in muscle). The hydrophilic carboxy-late groups stick out into the surrounding medium, while the majority of the molecule is embedded in a hydrophobic cleft in the protein, lined with amino acids such a leucine and valine. The octahedral coordination sphere of the iron(II) is completed with a histidine residue from the protein and an oxygen molecule. 

The liver also plays an essential role in dietary amino acid metabolism. The liver absorbs the majority of amino acids, leaving some in the blood for peripheral tissues. The priority use of amino acids is for protein synthesis rather than catabolism. By what means are amino acids directed to protein synthesis in preference to use as a fuel The K jyj value for the aminoacyl-tRNA synthetases is lower than that of the enzymes taking part in amino acid catabolism. Thus, amino acids are used to synthesize aminoacyl-tRNAs before they are catabolized. When catabolism does take place, the first step is the removal of nitrogen, which is subsequently processed to urea. The liver secretes from 20 to 30 g of urea a day. The a-ketoacids are then used for gluconeogenesis or fatty acid synthesis. Interestingly, the liver cannot remove nitrogen from the branch-chain amino acids (leucine, isoleucine, and valine). Transamination takes place in the muscle. 

Valine is involved with muscle function and muscle energy, fights acute physical stress, and aids assimilation of all other amino acids by the small intestine. 

Because the hver metabohzes the aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan), methionine, and glutamine, the plasma concentrations of these amino acids are elevated in cirrhotic patients. Plasma concentrations of the branched-chain amino acids (BCAAs) (i.e., valine, leucine, and isoleucine) often are depressed because these amino acids are metabohzed by skeletal muscle. This altered plasma aminogram contributes to the development of hepatic encephalopathy. 

C. Leucine but none of the other amino acids listed is a branched-chain amino acid. The muscle has a very active branched-chain amino acid metabolic pathway and uses that pathway to provide energy for its own use. The products of leucine metabolism are acetyl-CoA and acetoacetate, which are used in the tricarboxylic acid cycle. Acetoacetate is activated by succinyl-CoA and cleaved to two molecules of acetyl-CoA in the P-ketothiolase reaction. The other branched-chain amino acids, valine, and isoleucine, yield succinyl-CoA and acetyl-CoA as products of their catabolism. 

Certain amino acids are preferentially used in a tissue-specific manner. For example, skeletal muscle has a relatively high capacity for branched-chain amino acid (leucine, isoleucine, and valine) utilization. Following... 

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