kcat (sec). 500 A 300 100 80 60 R-Ć- The following kinetic data were obtained for this enzyme: 40 4 H 5 6 COO OH pka: 5.1 and 9.6 7 pH kcat/Km (mM¹ sec) 1000 100 8 9 10 4 B 5 pka: 5.5 and 8.9 6 7 PH R- 8 9 10 KIE (VND) 7 6 5 4 3 نا 2 OH H C 4 5 COO pka 6 - 9.4 7 8 PH 9 10 (i) Draw a scheme showing all the protonation states of E (depicted as E, ES, ESH, EH, EH2, etc.) and their equilibria, together with the actual conversion of S (substrate) into P (product), assuming a single intermediate (you do not have to put in the rate or equilibrium constants). (ii) Match up the 4 pKas in the figures, A and B, with the different protonation states. (Explain what the pKas in Figures A and B represent). (iii) The data in Figure C refers to the kinetic isotope effect on the keat, obtained when the H indicated in red in the reaction given above, is replaced with a deuterium. Why does Figure C show only one pka? Given the information in C, together with that of A and B, what can you conclude about the nature of active site residues and their roles in the mechanism?

kcat (sec). 500 A 300 100 80 60 R-Ć- The following kinetic data were obtained for this enzyme: 40 4 H 5 6 COO OH pka: 5.1 and 9.6 7 pH kcat/Km (mM¹ sec) 1000 100 8 9 10 4 B 5 pka: 5.5 and 8.9 6 7 PH R- 8 9 10 KIE (VND) 7 6 5 4 3 نا 2 OH H C 4 5 COO pka 6 - 9.4 7 8 PH 9 10 (i) Draw a scheme showing all the protonation states of E (depicted as E, ES, ESH, EH, EH2, etc.) and their equilibria, together with the actual conversion of S (substrate) into P (product), assuming a single intermediate (you do not have to put in the rate or equilibrium constants). (ii) Match up the 4 pKas in the figures, A and B, with the different protonation states. (Explain what the pKas in Figures A and B represent). (iii) The data in Figure C refers to the kinetic isotope effect on the keat, obtained when the H indicated in red in the reaction given above, is replaced with a deuterium. Why does Figure C show only one pka? Given the information in C, together with that of A and B, what can you conclude about the nature of active site residues and their roles in the mechanism?

Chemistry & Chemical Reactivity

10th Edition

ISBN:9781337399074

Author:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel

Publisher:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel

Chapter14: Chemical Kinetics: The Rates Of Chemical Reactions

Section14.7: Reaction Mechanisms

Problem 1.2ACP

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