Chymotrypsinogen is a:

Ans. d. Zymogen: (Ref: Lippincott 4/e p64, 443, 248-49; Harper 29/e p89, 519, 651-53)Chymotrypsinogen or prochymotrypsin is a proprotein, proenzyme or zymogen."Chymotrypsinogen or prochymotrypsin is a proprotein, proenzyme or zymogen. Trypsin can then activate chymotrypsinogen to chymotrypsin, proelastase to elastase. procarboxypeptidase to carboxypeptidase, and proaminopeptidase to aminopeptidase. Chymotrypsinogen is a endopeptidase, breaking the peptide bond formed by alpha carboxyl group of amino acids: phenylalanine, tyrosine, tryptophan, valine or leucine."Proproteins (Proenzymes or Zymogens)Zymogen is an inactive precursor of enzyme/protein that require selective proteolysis for activationQ.Selective proteolysis often result in conformational changes that create the catalytic site of an enzyme or it unmasks the active site of an enzyme by removing small region of peptide chain (by hydrolysis of specific peptide bond)Q.Enzymes needed intermittently but rapidly often are secreted in an initially inactive form since new synthesis and secretion of required proteins might be insufficiently rapid to respond to a pressing pathophysiological demand such as clot formation, clot dissolution, tissue repair etc.Proenzymes facilitate rapid mobilization of activity in response to physiological need.Proteolytic digestive enzymes are known as proteases. These are secreted as inactive zymogens. The synthesis of enzymes as Zymogens protects the cell from being digested by its own product (autodigestion)Q.Types of ProteasesExopeptidaseEndopeptidase* Hydrolyse peptide bonds one at a time from the ends of polypeptide chain.* Carboxypeptidase (in pancreatic juice): Cleaves amino acid from carboxy terminalQ* Aminopeptidase (in small intestine): Cleaves amino acid from amino terminalQ* Hydrolyse peptide bonds in mid portion between specific amino acids (Pepsin, Elastase, Trypsin, Chymotrypsin)Q