Enzyme Inhibition by Structural and Binding Mechanisms

Steps:

• PHBA's structural similarity to catechol suggests it mimics the substrate, blocking the active site without changing what the enzyme recognizes.
• PTU binds directly to the copper cofactor in the active site, preventing normal catalysis while maintaining the enzyme's substrate preference.
• Option 1 describes a change in what the enzyme binds, but inhibitors here block activity without altering recognition.
• Neither inhibitor denatures or modifies the enzyme's inherent specificity; they reduce rate by occupancy.

Why B is correct:

• Both inhibitors reduce activity by altering effective specificity through competitive blockade, fitting definition of site-specific inhibition without broad changes (per enzyme kinetics).

Why the others are wrong:

• A includes irrelevant mechanisms like 2 and 3, as only 1 applies.
• C focuses solely on competition, ignoring specificity alteration by cofactor binding.
• D relies on undefined 3, which lacks evidence.

Final answer: B