Fish Nutrition and Feed Technology (2+1)

Unit 14 - Digestive enzyme, digestibility and factors affecting digestibility

14.3.Protein digestion

Proteolytic enzymes arise from inactive precursors known as zymogens. Zymogens are processed in the lumen of the gut either by acid hydrolysis or proteolytic action. Proteases break down peptide link of proteins. Different enzymes are capable of acting on peptide bonds either at the end of protein (exopeptidases) or at a point within the protein (endopeptidases). Endopeptidases or very specific in their action and exert their effect only at a particular point with in the protein molecule.

For example pepsin hydrolyses the bond on the amino side of the aromatic radical, while chymotrypsin hydrolyses the bond on the carboxyl side. Trypsin on the other hand acts on peptide bonds between arginine and lysine, These three enzymes are probably the most important in the digestion of protein.