Competitive Inhibition in Enzyme Kinetics

Steps:

• Competitive inhibitors bind to the enzyme's active site, directly competing with the substrate.
• This competition reduces the enzyme's affinity for substrate, raising the apparent Km (substrate concentration needed for half Vmax).
• At saturating substrate levels, the inhibitor is displaced, allowing the enzyme to reach its full catalytic rate.
• Thus, Vmax remains unchanged while Km increases.

Why D is correct:

• In Michaelis-Menten kinetics, competitive inhibition elevates Km by the factor (1 + [I]/Ki) but leaves Vmax intact since excess substrate overcomes inhibition.

Why the others are wrong:

• A: Vmax does not increase; inhibitors cannot exceed the enzyme's intrinsic maximum velocity.
• B: Vmax stays the same in competitive inhibition, and Km rises rather than falls.
• C: Km increases due to reduced substrate affinity, not decreases.

Final answer: D