Question

The statement which is incorrect with respect to enzyme action is:

• A. Addition of a lot of succinate does not reverse the inhibition of succinic dehydrogenase by malonate
• B. The substrate binds with the enzyme at its active site
• C. A non-competitive inhibitor binds the enzyme at a site distinct from that which binds the substrate
• D. Malonate is a competitive inhibitor of succinic dehydrogenase

Answer 1

The correct option is A Addition of a lot of succinate does not reverse the inhibition of succinic dehydrogenase by malonate

Malonate is a competitive inhibitor of succinic dehydrogenase. The reaction is inhibited by malonate ions which have a very similar shape to succinate ions. The malonate ions therefore block the active site but that is reversible. The malonate ions will break away and free up the enzyme again. Substrate binds with enzyme at its active site.

A non competitive inhibitor binds the enzyme at a site distinct from the active site, the site which binds the substrate. Hence, it does not have any effect on the substrate concentration. This type of inhibition cannot be reversed by addition of more substrate.

A competitive inhibitor binds to the enzyme at the active site, the site which binds the substrate. This type of inhibition can be reversed by addition of more substrate. For example, malonate is a competitive inhibitor of succinic dehydrogenase. Succinate and malonate both binds to the same active site of the enzyme succinic dehydrogenase. Addition of a lot of succinate reverses inhibition of succinic dehydrogenase by malonate.