Non-competitive inhibitors reduce enzyme activity without affecting substrate binding

Steps:

• Recall non-competitive inhibitors bind to allosteric sites, not active sites.
• Determine impact on Km: unchanged, as active site affinity remains the same.
• Determine impact on Vmax: decreased, as fewer enzyme molecules are active.
• Assess reversibility: inhibition persists even at high substrate concentrations.

Why D is correct:

• Non-competitive inhibition lowers Vmax (effect 2) and cannot be overcome by excess substrate (effect 3), per Michaelis-Menten kinetics where Km is unaffected.

Why the others are wrong:

• A includes 1 (Km increase), which applies to competitive inhibition only.
• B includes 1 (Km increase), incorrect for non-competitive.
• C excludes 2 (Vmax decrease), a key effect of non-competitive inhibition.

Final answer: D