You measure the rate of an enzyme-catalyzed reaction that involves formation of a covalent bond between the substrate and a deprotonated cysteine residue on the enzyme. In steady- state kinetic studies, a mutant enzyme bearing a substitution of this cysteine to alanine displays a large decrease in catalytic efficiency. What is the MOST likely explanation for this result?
A. The decrease in catalytic efficiency is most likely caused by a decreased affinity of the mutant enzyme for the substrate.
B. The decrease in catalytic efficiency is most likely caused by a large decrease in kcat.
C. It is not possible for an enzyme lacking a major catalytic side chain to perform a reaction. The data must be incorrect.
D. The cysteine is likely acting as an electrophile to attack the substrate and form the covalent intermediate.
E. The decrease in catalytic efficiency likely results from the alanine residue forming a covalent intermediate that cannot be decomposed.
Expert Answer
Option B , The decrease in catalytic effic…View the full answer
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