Answered: Many enzyme mechanisms involve…

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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$Many enzyme mechanisms involve transferring protons. Sidechains of an enzyme can act as catalytic acids or catalytic bases in this process. The figure below shows a step in the reaction by the enzyme triose phosphate isomerase. Glu165 group. -OH Would a catalytic acid gain or lose a proton? Which sidechain in the mechanism is acting as a catalytic acid? co CH,OPO, 2- Activity remaining (%) Would a catalytic base gain or lose a proton? Which sidechain in the mechanism is acting as a catalytic base? 100 Curve I 8 Glu¹65 9 Below are two pH rate profiles showing the percent activity as a function of pH. Answer the questions below about how these curves relate to the mechanism of triose phosphate isomerase. Remember what fraction of a titratable group is unprotonated at the pka. 10 OH In this reaction a carbonyl is converted into an enol intermediate. Circle the enol 100 Activity remaining (%) H Curve 2 CIOH CIOH CH₂OPO,²- 8 9 N N 10 7 pH PH i) Which of these curves shows the pH rate profile of Glu-165? Explain your answer His95 ii) How does the pKa of Glu-165 in the enzyme compare with the pKa of the sidechain in solution? iii) Which of these curves shows the pH rate profile of His-95? Explain your answer$

Transcribed Image Text:Many enzyme mechanisms involve transferring protons. Sidechains of an enzyme can act as catalytic acids or catalytic bases in this process. The figure below shows a step in the reaction by the enzyme triose phosphate isomerase. Glu165 group. -OH Would a catalytic acid gain or lose a proton? Which sidechain in the mechanism is acting as a catalytic acid? co CH,OPO, 2- Activity remaining (%) Would a catalytic base gain or lose a proton? Which sidechain in the mechanism is acting as a catalytic base? 100 Curve I 8 Glu¹65 9 Below are two pH rate profiles showing the percent activity as a function of pH. Answer the questions below about how these curves relate to the mechanism of triose phosphate isomerase. Remember what fraction of a titratable group is unprotonated at the pka. 10 OH In this reaction a carbonyl is converted into an enol intermediate. Circle the enol 100 Activity remaining (%) H Curve 2 CIOH CIOH CH₂OPO,²- 8 9 N N 10 7 pH PH i) Which of these curves shows the pH rate profile of Glu-165? Explain your answer His95 ii) How does the pKa of Glu-165 in the enzyme compare with the pKa of the sidechain in solution? iii) Which of these curves shows the pH rate profile of His-95? Explain your answer

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