Competitive inhibitors raise Km by competing for the active site

Steps:

• Competitive inhibitors bind reversibly to the enzyme's active site, directly competing with substrate molecules.
• This competition reduces the enzyme's apparent affinity for the substrate at lower concentrations.
• Km, defined as the substrate concentration yielding half of Vmax, increases because higher substrate levels are needed to outcompete the inhibitor.
• Vmax remains unchanged, as sufficient substrate can fully saturate the enzyme.

Why A is correct:

• Km increases per Michaelis-Menten kinetics, as the inhibitor effectively lowers substrate binding affinity by occupying the active site.

Why the others are wrong:

• B: Vmax is unaffected; competitive inhibition only alters Km, not maximum velocity.
• C: Km is increased, even though high substrate overcomes inhibition to reach Vmax.
• D: Competitive inhibitors bind specifically to the active site, not elsewhere.

Final answer: A