Chymotrypsinogen is converted to chymotrypsin by-

Ans. is 'c' i.e., Trypsin * The digestion of proteins begins in the stomach Pepsin is a proteolytic enzyme which is secreted by chief cells of stomach in an inactive (zymogen) form i.e., pepsinogen. Acid in the lumen of stomach converts pepsinogen to active pepsin. Pepsin once formed also attacks pepsinogen producing more pepsin molecules by autocatalysis. Pepsin breaks some of the food protein into smaller units called peptides.* Further digestion of proteins is brought about pancreatic enzymes. Pancreatic enzymes are secreted in an inactive (Zymogen) form. These are trypsinogen, chymotrypsinogen proelastase, procarboxy-peptidase A and procarboxypeptidase B. Trypsinogen is initially activated by enterokinase (enteropeptidase), an enzyme present in brush border of small intestinal epithelial cells. The conversion of inactive trypsinogen into active trypsin requires removal of an N-terminal peptide by enteropetidase (enterokinase). Once some trypsin has been generated by enterokinase, it can activate more trypsinogen as well as other inactive enzymes.