In Michaelis-Menten kinetics, an inhibitor increases Km without changing Vmax. A second inhibitor decreases Vmax without changing Km. Which inhibition types are described respectively?

• A Competitive inhibition; uncompetitive inhibition
• B Uncompetitive inhibition; noncompetitive inhibition
• C Noncompetitive inhibition; competitive inhibition
• D Competitive inhibition; noncompetitive inhibition ✓

Explanation

Competitive inhibitors bind only the free enzyme at the active site (competing with substrate); increasing substrate concentration can overcome inhibition. They increase apparent Km (reduced substrate affinity) while Vmax remains unchanged. Noncompetitive inhibitors bind an allosteric site on both free enzyme and enzyme-substrate complex equally; increasing substrate cannot overcome inhibition. They decrease Vmax while Km is unchanged. Uncompetitive inhibitors bind only the enzyme-substrate complex, decreasing both Km and Vmax proportionally (lines on Lineweaver-Burk plot are parallel for uncompetitive inhibition). This distinction is fundamental and frequently tested in NEET PG enzyme kinetics.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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