Non-competitive inhibition reduces Vmax without changing Km

Steps:

• Identify non-competitive inhibition: binds allosteric site, decreases enzyme activity regardless of substrate binding.
• Recall Michaelis-Menten effect: curve reaches lower maximum velocity, but Km (substrate for half Vmax) stays same.
• Compare to uninhibited: inhibited line plateaus lower, crosses half its Vmax at original Km.
• Rule out alternatives: competitive raises Km (same Vmax); uncompetitive lowers both; no change is uninhibited.

Why D is correct:

• D shows curve with unchanged Km but reduced Vmax, matching non-competitive definition where inhibitor affects catalysis, not substrate binding (V = Vmax [S] / (Km + [S]), Vmax lowered by factor (1 + [I]/Ki)).

Why the others are wrong:

• A: Depicts competitive inhibition (higher Km, same Vmax).
• B: Shows uncompetitive inhibition (parallel lines in Lineweaver-Burk, lowers both Km and Vmax).
• C: Represents no inhibition (unchanged curve).

Final answer: D