In a metabolic pathway, succinate dehydrogenase catalyses the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount of succinate molecules to those of malonic acid reduces the inhibitory effect of malonic acid. What role does malonic acid play with respect to succinate dehydrogenase?
A) Malonic acid is a competitive inhibitor.
B) Malonic acid blocks the binding of fumarate.
C) Malonic acid is a noncompetitive inhibitor.
D) Malonic acid is an allosteric regulator.

Question

Quizplus · Accepted Answer

Malonic acid inhibits succinate dehydrogenase by acting as a competitive inhibitor, as it resembles succinate and competes with it for the active site of the enzyme. Increasing the concentration of succinate molecules can reduce the inhibitory effect of malonic acid by outcompeting it for the enzyme's active site. Malonic acid does not block the binding of fumarate and is not a noncompetitive inhibitor. It is also not an allosteric regulator because it does not bind to a different site on the enzyme to change its shape and activity.

In a Metabolic Pathway, Succinate Dehydrogenase Catalyses the Conversion of Succinate