ATP synthase (Complex V) utilises the proton motive force. The F0 component contains a rotating c-ring. For ATP synthesis in human mitochondria, how many protons must pass through the F0 channel to synthesise one molecule of ATP?

• A 2 protons per ATP, corresponding to the stoichiometry of the alpha-beta conformational change
• B Approximately 8 protons per ATP, based on the human F0 c-ring having 8 c-subunits requiring one proton per c-subunit per 360° rotation, with 3 ATP per rotation ✓
• C Exactly 3 protons per ATP in all organisms regardless of c-ring size
• D 10 protons per ATP, because each of the 5 beta-subunits in the F1 domain requires 2 protons for its conformational cycle

Explanation

The number of protons required per ATP depends on the c-ring stoichiometry. The human mitochondrial F0 c-ring has 8 c-subunits. Each complete rotation (requiring one proton per c-subunit = 8 protons) drives the synthesis of 3 ATP (since the F1 alpha3beta3 head has 3 catalytic beta subunits synthesising 1 ATP per 120° rotation). Therefore, 8 protons ÷ 3 ATP = approximately 2.67 protons per ATP, often stated as 8H⁺ for 3 ATP. This explains why total mitochondrial ATP yield calculations yield approximately 30–32 ATP per glucose (not the older textbook value of 36–38).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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