Food Chemistry and Fish in Nutrition ( 2+1)

8.2.2. Amino aciid catabolism

8.2.2.Metabolic fate of Amino acid

Intracellular proteases hydrolyze internal peptide bonds of protein, releasing peptides, which are then degraded to free amino acids by peptidases. Endopeptidases cleave internal bonds, forming shorter peptides. Aminopeptidases and carboxypeptidases remove amino acids sequentially from the amino acids. Extra cellular, membrane-associated, and long-lived intracellular proteins are degraded in cellular organelles termed lysosomes by ATP- independent processes. By contrast, degradation of abnormal and other occurs in the cystol.

Animals excrete nitrogen from amino acids and other sources as one of three end products: ammonia, uric acid, or urea. Teleostean fish, which are ammonotelic, excrete nitrogen as ammonia. Land animals convert nitrogen either to uric acid (uricotelic organisms) or to urea (ureotelic organisms) and excreted in urine.

Free amino acids released from dietary or intracellular proteins are metabolized in identical ways. Following removal of the α -amino nitrogen by transamination, the resulting carbon “Skeleton” is then degraded

There are four stages in the metabolism of amino acids are (1) transamination, (2) deamination (3) ammonia formation and transport, and (4) synthesis of urea by urea cycle.