The catalytic mechanism of an enzyme found in the mitochondrial matrix (pH = 7.8) depends on an active site Lys residue (pKa = 9.5) that acts as a general acid. Mutation of a neighboring residue alters the microenvironment of the Lys side chain so that its pKa shifts from 9.5 to 7.4. (a) Calculate the ratio of protonated to deprotonated Lys at pH 7.8 for the normal and mutant enzyme. (b) Would you expect the mutation to increase or decrease the reaction rate? Explain your answer. (c) Lys is a classified as a basic amino acid, but it commonly acts as an acid catalyst in biochemical reactions. Explain this paradox.
The catalytic mechanism of an enzyme found in the mitochondrial matrix (pH = 7.8) depends on an active site Lys residue (pKa = 9.5) that acts as a general acid. Mutation of a neighboring residue alters the microenvironment of the Lys side chain so that its pKa shifts from 9.5 to 7.4. (a) Calculate the ratio of protonated to deprotonated Lys at pH 7.8 for the normal and mutant enzyme. (b) Would you expect the mutation to increase or decrease the reaction rate? Explain your answer. (c) Lys is a classified as a basic amino acid, but it commonly acts as an acid catalyst in biochemical reactions. Explain this paradox.
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
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The catalytic mechanism of an enzyme found in the mitochondrial matrix (pH = 7.8) depends on an active site Lys residue (pKa = 9.5) that acts as a general acid. Mutation of a neighboring residue alters
the microenvironment of the Lys side chain so that its pKa shifts from 9.5 to 7.4.
(a) Calculate the ratio of protonated to deprotonated Lys at pH 7.8 for the normal and mutant enzyme.
(b) Would you expect the mutation to increase or decrease the reaction rate? Explain your answer.
(c) Lys is a classified as a basic amino acid, but it commonly acts as an acid catalyst in biochemical reactions. Explain this paradox.
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