The protein complexes in the cristae that contribute to the H+ gradient (electromotive force) across the cristae membrane include; complexes I (NADH/ubiquinone oxidoreductase), II (succinate dehydrogenase), III (cytochrome c reductase) and IV (cytochrome c oxidase).
Complex I feeds an electron from NADH to a quinol molecule ( concomitantly pumping four protons from the matrix into the crista lumen). Complex III transfers the electron from quinol to cytochrome C (concomitantly pumping one proton). Complex IV transfers the electron from cytochrome c to an oxygen molecule (concomitantly forming a water molecule and pumps four protons).
This H+ gradient is then harnessed by ATP synthase to form ATP by phosphorylating ADP.
NADH+H+ → Complex I → Q → Complex III → cytochrome c → Complex IV → H2O
↑
Complex II
↑
Succinate
