Two statements in respect of drug-enzyme interaction are given below
Statement I: Action of an enzyme can be blocked only when an inhibitor blocks the active site of the enzyme.
Statement II: An inhibitor can form a strong covalent bond with the enzyme.
In the light of the above statements, choose the correct answer from the options given below

We need to evaluate both statements about drug-enzyme interaction.

Statement I: "Action of an enzyme can be blocked only when an inhibitor blocks the active site of the enzyme."

This statement is false. While competitive inhibitors work by blocking the active site (the site where the substrate normally binds), there are also non-competitive inhibitors that bind at an allosteric site (a site different from the active site). When a non-competitive inhibitor binds at the allosteric site, it changes the shape of the enzyme, which in turn alters the shape of the active site, making the substrate unable to bind properly. So the action of an enzyme can be blocked by inhibitors that bind at sites other than the active site as well.

Statement II: "An inhibitor can form a strong covalent bond with the enzyme."

This statement is true. Certain drugs act as irreversible inhibitors that form strong covalent bonds with amino acid residues in the enzyme's active site or other critical regions. For example, aspirin irreversibly acetylates the enzyme cyclooxygenase (COX) by forming a covalent bond. Once a covalent bond is formed, the enzyme is permanently inactivated and cannot catalyze its reaction until new enzyme molecules are synthesized.

Since Statement I is false and Statement II is true, the correct choice is the one that reflects this.

Hence, the correct answer is Option D.