2. Chymotrypsin, trypsin, and elastase are members of a family of enzymes referred to as serine proteases. The enzyme papain (found in papaya) is also a protease but is a member of a family of enzymes referred to as cysteine proteases. The amino acid residues in the active site of papain critical for peptide bond hydrolysis are a protonated histidine and a deprotonated cysteine residue. The cysteine residue functions as the nucleophile similarly to the serine residue in serine proteases. (a) Using what you know about chymotrypsin's mechanism, draw a reaction mecha- nisn for the hydrolysis of a peptide bond by papain. Does the mechanism you have drawn employ acid-base catalysis, covalent catalysis, (b) or both? (c) The pka values of the active site residues that control the pH profile of the activity of pa pain are 4.2 and 8.2. The pH optimum for the reaction is 6.0. Through the many years of re- search carried out on cysteine proteases, it has been demonstrated that the pKa of 4.2 belongs to the nucleophilic -SH group and the pka of 8.2 belongs to the active site histidine residue. These pKa values are not commonly associated with these residues. What are the pKa values associated with the same ionizing groups in the corresponding free amino acids and why are the values of 4.2 and 8.2 consistent with the mechanism of the enzyme? (d) Natives of tropical countries who cooked meat wrapped in papaya leaves noted that the meat was more tender as a result. Provide a biochemical explanation for this obser- vation. (e) In Adolph's Meat Tenderizer®, available in most grocery stores, the "Tenderizer" Ingredient is named bromelain. What is bromelain?

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Transcribed Image Text:2. Chymotrypsin, trypsin, and elastase are members of a family of enzymes referred to as serine proteases. The enzyme papain (found in papaya) is also a protease but is a member of a family of enzymes referred to as cysteine proteases. The amino acid residues in the active site of papain critical for peptide bond hydrolysis are a protonated histidine and a deprotonated cysteine residue. The cysteine residue functions as the nucleophile similarly to the serine residue in serine proteases. (a) Using what you know about chymotrypsin's mechanism, draw a reaction mecha- nisn for the hydrolysis of a peptide bond by papain. Does the mechanism you have drawn employ acid-base catalysis, covalent catalysis, (b) or both? (c) The pKa values of the active site residues that control the pH profile of the activity of pa- pain are 4.2 and 8.2. The pH optimum for the reaction is 6.0. Through the many years of re- search carried out on cysteine proteases, it has been demonstrated that the pKa of 4.2 belongs to the nucleophilic -SH group and the pKa of 8.2 belongs to the active site histidine residue. These pka values are not commonly associated with these residues. What are the pKa values associated with the same ionizing groups in the corresponding free amino acids and why are the values of 4.2 and 8.2 consistent with the mechanism of the enzyme? (d) Natives of tropical countries who cooked meat wrapped in papaya leaves noted that the meat was more tender as a result. Provide a biochemical explanation for this obser- vation. (e) In Adolph's Meat Tenderizer®, available in most grocery stores, the "Tenderizer" Ingredient is named bromelain. What is bromelain?

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