Which of the following enzymes is stable at acidic pH-
Correct Answer: Pepsinogen
Description: Ans. is 'a' i.e., PepsinogenPepsinogen* Pepsinogen is an enzyme secreted by gastric chief cells.* It is secreted in an inactive pepsinogen form and is then converted into active pepsin in the presence of hydrochloric acid, which is secreted by parietal cells.* It acts on aromatic aminoacid - X linkage. It converts proteins of the diet into partially digested oligopeptides and polypeptides.* The optimum pH of pepsin is 1.6 to 3.2, since it is supposed to be active in the acidic pH of gastric juice. Hence it is active till the food reaches the duodenal cap.Pancreatic enzymes* Trypsinogen, chymotrypsinogen proelastase are endopeptidases released by exocrine part of pancreas.* Procarboxypeptidase A and Procarboxypeptidase B are exopeptidases released by exocrine part of pancreas.* All these pancreatic enzymes are active in alkaline pH as pancreatic juice is alkaline* Trypsinogen gets activated to form trypsin by enterokinase of intestinal juice after the pancreatic juice reaches the second part of the duodenum* Trypsin acts on Lys-X & Arg-X linkage.* Additionally trypsin activates chymotrypsinogen, proelastase, procarboxypeptidase A and procarboxypeptidase B to form the active forms - chymotrypsin, elastase, carboxypeptidase A and carboxypeptidase B* Chymotrypsin like pepsin acts on Aro-X linkage* Elastase acts on a broad range of peptide linkages.* Carboxypeptidase A acts on the carboxyterminal end of proteins or partially digested protein products of the carboxyterminal end is contributed by aromatic amino acids - Phe, Tyr, Try.* Carboxypeptidase B acts on the carboxyterminal end of proteins or partially digested protein products of the carboxyterminal end is contributed by branched chain amino acids like Val, Leu, lie* Other enzymes which are active in acidic pH are lysosomal enzymes and acid phosphatase.
Category:
Biochemistry
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