You are conducting an experiment on mitochondrial respiration. You add malate/pyruvate and respiration is normal. You add succinate and respiration is normal. When you add another substance in the presence of pyruvate/succinate and malate, respiration is blocked. Which of the following substances is most likely added?

Options

1. Rotenone
2. Antimycin A
3. Oligomycin
4. 2,4-dinitrophenol

Correct Answer

Oligomycin

Explanation

Oligomycin is an inhibitor of ATP synthase (Complex V) in the electron transport chain. When added, it blocks the flow of protons through ATP synthase, thereby inhibiting ATP production and causing respiration to cease. Since both NADH-linked substrates (malate/pyruvate) and FADH2-linked substrates (succinate) are working normally before oligomycin addition, the inhibition must be at the final common pathway of ATP synthesis.

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