Organic acids physiological actions

Since L-tryptophan is an indispensable amino acid, its role as a substrate for protein synthesis is necessarily of much importance. However, L-tryp-tophan has other roles that are vital in maintaining normal physiological functions. For example, L-tryptophan has been reported to play a unique role in regulating protein synthesis, particularly in the liver, but also in other organs in a manner unrelated to its function as a precursor amino acid. This action of L-tryptophan is reviewed in this chapter. 

The human plasma metallo-protease carboxypeptidase N (CPN, arginine carboxypeptidase, anaphylatoxin inactivator, kininase I, EC 3.4.17.3) catalyzes the release of the basic amino acids lysine and arginine from the C-termini of peptides and proteins such as bradykinin and kallidin [95], the anaphylatoxins C3a, C4a, and C5a [96,97], fibrinopeptides 6A and 6D [98], hexapeptide enkephalins [99], protamine [100], and the creatine kinase MM-isoenzyme [101,102]. Its most likely physiological function is to protect the organism from the actions of potent peptides, which may escape from tissues or be released in the circulation. 

Structure and physiology of the kidney glomerular filtration tubular activity selective reabsorption and secretion, often using specific carrier mechanisms carbonic anhydrase and acid-base balance. The kidney also produces, and is sensitive to, hormones actions of the hormones ADH, aldosterone and PTH the kidney as a secretory organ erythropoietin, the renin-angiotensin system vitamin D3. 

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