In the classic kinetic experiment, addition of malonate to mitochondria respiring on succinate slows oxygen consumption. Increasing succinate concentration restores the rate. Malonate is best described as:

• A An irreversible inhibitor of succinate dehydrogenase
• B A non-competitive inhibitor of fumarase
• C An uncoupler of oxidative phosphorylation
• D A competitive inhibitor of succinate dehydrogenase ✓

Explanation

Malonate structurally resembles succinate but lacks the methylene group needed for dehydrogenation, so it occupies the active site of succinate dehydrogenase without reacting. Because inhibition can be overcome by raising substrate concentration, apparent Km increases while Vmax stays constant, the signature of competitive inhibition. Irreversible inhibitors cannot be reversed by excess substrate, and malonate does not collapse the proton gradient.

Reference: Lehninger Principles of Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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