Which one of the following statements regarding enzyme inhibition is correct?
- Competitive inhibition is seen when a substrate competes with an enzyme for binding to an inhibitor protein.
- Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme.
- Non-competitive inhibition of an enzyme can be overcome by adding large amount of substrate.
- Non-competitive inhibitors often bind to the enzyme irreversibly.
Answer
(2) Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme.
Solution
As per NCERT, when the binding of a chemical shuts off enzyme activity, the process is called inhibition; when the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as a competitive inhibitor (e.g. malonate inhibits succinic dehydrogenase).
⇒ Because of this resemblance, the inhibitor competes with the substrate for the active site of the enzyme — statement (2).
∵ (1) reverses the roles of enzyme and substrate; (3) is true of competitive (not non-competitive) inhibition; (4) non-competitive inhibitors usually bind reversibly at a site other than the active site.
Answer: (2)