The Biology Project: Biochemistry

Energy, Enzymes, and Catalysis Problem Set

Problem 9 Tutorial: Kinetics of an enzyme reaction with a non-competitive inhibitor.

Which of the following graphs shows the results of reaction rate vs substrate concentration for an non-allosteric enzyme in the absence and presence of a noncompetitive inhibitor (noncompetitive inhibitors bind to an enzyme at a site different than the active site)?

Noncompetitive inhibition of an enzyme can occur when an inhibitor binds to an enzyme at a site other than the active site. The noncompetitive inhibitor slows down the reaction rate, i.e. the rate of the product formation is less with inhibitor present than with inhibitor absent. This means that the active site is modified, but not disabled, by the presence of the inhibitor.

As shown in graph #2, the effect of noncompetitive inhibitor cannot be overcome with high substrate concentration. Since the inhibitor and substrate are not competing for the same binding site on the enzyme, a noncompetitive inhibitor reduces the reaction rate at all substrate concentrations.

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