Amino Acid Pools and Protein Turnover

2 AMINO ACID POOLS AND PROTEIN TURNOVER 20.2.1 Interorgan Amino Acid Traffic 

Portal circulation carries amino acids to the liver, and the general circulation then distributes them throughout the organism. The amino acid content of plasma depends on the dietary state of the individual. After a meal, the free amino acid concentration in plasma increases by about 200-250% compared with that seen 

Each tissue, including the bloodstream, has a free amino acid pool. This amounts to a total of about 100 g. By far the largest fraction, 50-80%, is located in muscle. Kidney accounts for about 4%, liver for 10%, and the bloodstream another 4%. Glutamine and glutamate are major components of such pools. Free amino acid pools are in equilibrium with tissue protein. Tissue proteins are in a constant state of turnover, that is, biosynthesis and degradation from and to free amino acids. Only plasma proteins, which are largely synthesized in the liver, are not in equilibrium with the plasma free amino acid pool. 

Compound Amount excreted (g) Total nitrogen excreted (%) 

Source From Varley H. Practical Clinical Biochemistry. New York Interscience, 1963. 

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Anno acid catabolism is part of the larger process of whole body nitro gan metabolism. Nitrogen enters the body in a variety of compounds present in food, the most important being amino acids contained in detary protein. Nitrogen leaves the body as urea, ammonia, and other products derived from amino acid metabolism. The role of body proteins in these transformations involves two important concepts the amino acid pool and protein turnover. 

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