Which statement about enzyme inhibition is correct?

• A. Competitive inhibitors bind to the active site but do not resemble the substrate.
• B. Noncompetitive inhibitors bind to the active site and block substrate binding.
• C. Competitive inhibitors always increase Vmax.
• D. Noncompetitive inhibitors bind to a site other than the active site and alter its conformation.

Answer: (D)

Noncompetitive inhibition works by binding to a site other than the active site and changing the enzyme’s shape, which reduces the enzyme’s ability to convert substrate to product. Because this inhibitor doesn’t block substrate binding, Km stays about the same, but Vmax decreases since fewer enzymes are effectively catalyzing the reaction. The other statements misstate how inhibition works: competitive inhibitors resemble the substrate and compete for the active site, which affects Km but not Vmax; noncompetitive inhibitors do not block substrate binding; and competitive inhibitors do not increase Vmax. Therefore, the description of binding away from the active site and altering conformation correctly captures the mechanism.