 Respiratory complex III

Respiratory complex III, the cytochrome bc1 complex, transfers electrons from ubiquinol to cytochrome c. Its Q-cycle mechanism separates the two electrons from a quinol and couples their transfer to vectorial proton movement.

Cytochrome c carries one electron at a time, whereas ubiquinol carries two. The mechanism therefore connects carriers with different electron stoichiometries while contributing to the membrane electrochemical gradient.