Question

Malonate is an inhibitor of the enzyme succinate dehydrogenase. How would you determine whether malonate is a competitive inhibitor or a non-competitive inhibitor?

Short answer

Malonate is an inhibitor of the enzyme succinate dehydrogenase. The addition of substrate facilitates the reaction, which increases the reaction rate. The rate of reaction is increased due to the competition between the inhibitor and substrate.

Step-by-step solution

Description of succinate dehydrogenase

Succinate dehydrogenase is the enzyme present in both prokaryotes and eukaryotes. It participates in the citric acid cycle and electron transport chain. The enzyme succinate dehydrogenase mediates the conversion of succinate into fumarate.

Competitive and non-competitive inhibitor 

An inhibitor is a substance that tends to block enzymatic activity. The chemical reaction is interrupted by the inhibition of one substance by the other substance by competing with it, and it is the mechanism of competitive inhibition.

A non-competitive inhibitor does not interrupt the binding of the substrate with the enzyme. Instead, it binds to the enzyme and alters the shape of the action, which in turn inhibits the enzymatic reaction.

Malonate as a competitive inhibitor 

Malonate is a substance that competes with succinate to inhibit succinate dehydrogenase. It is proved by adding additional substrate succinate to the reaction.

The addition of substrate tends to increase the reaction rate. If the reaction rate increases, then malonate is the competitive inhibitor of this enzyme. The substrate addition creates competition for the malonate to bind to the enzyme, increasing the reaction rate.

Hence, malonate is the competitive inhibitor of succinate dehydrogenase, which is confirmed by the addition of the substrate succinate.