Non-competitive inhibition reduces enzyme activity without affecting substrate binding

Steps:

• Define non-competitive inhibition: inhibitor binds to allosteric site, not active site.
• Recall kinetic effects: lowers Vmax by reducing active enzyme fraction, but Km unchanged as substrate affinity intact.
• Match to choices: identify option stating decreased Vmax with constant Km.
• Eliminate mismatches based on competitive inhibition traits.

Why C is correct:

• Non-competitive inhibitors decrease Vmax (fewer functional enzymes) while Km remains constant, per Michaelis-Menten kinetics where Km reflects substrate-enzyme affinity unaffected by allosteric binding.

Why the others are wrong:

• A: Binding to active site describes competitive inhibition, not non-competitive.
• B: Increasing Km indicates reduced substrate affinity, characteristic of competitive inhibition.
• D: Unchanged Vmax with increased Km fits competitive inhibition, not non-competitive.

Final answer: C