Enzyme Inhibition: Which types can occur in biochemical reactions?

Introduction:
Enzyme inhibition regulates metabolic flux, enables pharmacological control, and reveals mechanisms of catalysis. Inhibition can be temporary or permanent, and this question tests recognition of the main categories.

Given Data / Assumptions:

• Standard biochemical classification of inhibitors.
• Focus on whether inhibition can be reversible, irreversible, or both.

Concept / Approach:

Reversible inhibitors bind non-covalently (competitive, non-competitive, uncompetitive, mixed), allowing dissociation and restoration of activity. Irreversible inhibitors usually form covalent bonds with catalytic residues (e.g., serine in serine proteases) or bind so tightly that dissociation is negligible on experimental timescales.

Step-by-Step Solution:

Verification / Alternative check:

Classic examples include competitive reversible inhibition by methotrexate on dihydrofolate reductase, and irreversible inhibition by aspirin acetylating cyclooxygenase active-site serine.

Why Other Options Are Wrong:

A: Excludes irreversible inhibitors. B: Excludes reversible inhibitors. D: Contradicts abundant evidence. E: Allosteric activation is not inhibition and can be reversible; it does not preclude inhibition.

Common Pitfalls:

Equating irreversible with only covalent (some near-irreversible tight binding exists), or assuming reversible equals only competitive (there are multiple reversible modes).

Final Answer:

Both reversible and irreversible inhibition