Oligomycin is added to isolated mitochondria respiring on pyruvate. Oxygen consumption falls to nearly zero shortly after addition. This occurs because oligomycin:

• A Inhibits the exchange of ADP for ATP across the inner membrane
• B Directly inhibits NADH dehydrogenase at Complex I
• C Uncouples oxidative phosphorylation, wasting energy as heat
• D Inhibits the F0 proton channel of ATP synthase, causing the proton gradient to build until electron transport halts ✓

Explanation

Oligomycin binds the F0 stalk region of ATP synthase and plugs the proton channel. Protons can no longer flow back into the matrix, so the electrochemical gradient rises steeply and pumping protons against it becomes energetically impossible, secondarily stopping electron transport and oxygen consumption. An uncoupler such as dinitrophenol reverses this by collapsing the gradient, restoring respiration even in the presence of oligomycin.

Reference: Lehninger Principles of Biochemistry (Nelson and Cox), 7th ed.

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