Allopurinol as a competitive inhibitor of xanthine oxidase

Steps:

• Recall that allopurinol treats gout by inhibiting xanthine oxidase, the enzyme converting hypoxanthine to xanthine and then uric acid.
• Identify the mechanism: allopurinol structurally mimics hypoxanthine, binding to the enzyme's active site.
• Compare choices to competitive inhibition, where the inhibitor competes directly with substrate for the active site.
• Select the option matching this binding and reduced uric acid production.

Why A is correct:

• Competitive inhibition definition: inhibitor binds active site, blocking substrate (hypoxanthine) access and halting uric acid formation.

Why the others are wrong:

• B: Describes non-competitive inhibition, not allopurinol's mechanism.
• C: No evidence of hydrogen bond disruption; sentence is incomplete and inaccurate.
• D: Hydrolysis would irreversibly destroy enzyme, unlike allopurinol's reversible action.

Final answer: A