Question

Which one of the following statements regarding enzyme inhibition is correct?

• A. Non-competitive inhibitors often bind to the enzyme irreversibly.
• B. Competitive inhibition is seen when a substrate competes with an enzyme for binding to an inhibitor protein.
• C. Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme.
• D. Non-competitive inhibition of an enzyme can be overcome by adding a large amount of substrate.

Answer 1

The correct option is C Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme.

Competitive inhibition is when the substrate and the inhibitor compete for the active site on the enzyme as the inhibitor resembles the structure of the substrate. These inhibitors are also called substrate analogues. The competitive inhibitors decrease the interaction between the substrate and enzyme. E.g., Malonic acid is a competitive inhibitor for succinic acid dehydrogenase enzyme in Krebs cycle. Malonic acid resembles succinic acid in its structure and the enzyme succinic acid dehydrogenase is unable to differentiate the substrate and the inhibitor.
Non-competitive inhibition is seen when the inhibitor does not resemble the substrate in structure, but they decrease the activity of the enzyme. They bind to the enzyme at a place other than the active site, thereby changing the conformation of the active site. E.g., salts of heavy metals and cyanide.