Amino acid degradation leucine

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), unlike the other amino acids, are degraded only in extrahepatic tissues. 

The failure of amino acid degradation to go to completion and the relation between maximal destruction and temperature might be attributed to the fact that individual amino acids reacted at different rates at different temperatures. For example certain amino acids, leucine, arginine, methionine, and lysine showed little or no detectable reaction at 100°C after one hour, while others were reactive at this temperature(Table X). At higher temperatures, rate of amino acid degradation was measurable and proportional to the temperature of the reaction. 

The amino acids valine, leucine, isoleucine, and lysine are essential for mammals and are synthesized primarily in plant and bacterial cells. None of these amino acids is known to play significant roles other than as protein constituents and as substrates for their own degradation. 

Various pathways are employed for the degradation of branched-chain fatty acids, some of which arise from the metabolism of the branched-chain amino acids (see Leucine). Short-chain fatty adds are converted to their feitty acyl derivatives within the mitochondria, but long-chain fatty adds can be activated only by the endoplasmic reticulum and outer mi-tochondritd membrane. Long-chain acyl-CoA caimot penetrate the itmer mitochondrial membrane, and must be transported into the mitochondria as acyl-camitine (Fig. 3). 

Inherited defects in the enzymes of (3-oxidation and ketogenesis also lead to nonketotic hypoglycemia, coma, and fatty hver. Defects are known in long- and short-chain 3-hydroxyacyl-CoA dehydrogenase (deficiency of the long-chain enzyme may be a cause of acute fetty liver of pr nancy). 3-Ketoacyl-CoA thiolase and HMG-CoA lyase deficiency also affect the degradation of leucine, a ketogenic amino acid (Chapter 30). 

The long tail of myosin contains a high proportion of the amino acids leucine, isoleucine, aspartate and glutamate. These are released upon the degradation of myosin by intracellular proteases and peptidases and they provide nitrogen for the synthesis of glutamine. It is then stored in muscle and is a very important fuel for immune cells (Chapter 17). 

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