Atractyloside, a plant glycoside, blocks oxidative phosphorylation even though the electron transport chain itself remains fully functional. Its site of action is:

• A The Fo proton channel of ATP synthase
• B The phosphate carrier protein
• C Complex III at the ubiquinone oxidation site
• D The adenine nucleotide translocase (ANT) of the inner membrane ✓

Explanation

ATP synthesized inside the matrix must be exchanged for cytosolic ADP by the adenine nucleotide translocase. Atractyloside binds ANT and locks it, so ADP cannot enter the matrix and ATP synthesis stops despite an intact chain and proton gradient. Oligomycin acts at Fo, antimycin at Complex III, and mersalyl-type agents affect the phosphate carrier, making those distinct pharmacologic sites.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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