Palmitate decreases proton pumping of liver-type cytochrome c oxidase

The H+/e(-) stoichiometry of reconstituted cytochrome c oxidase from bovine kidney, containing subunit VIaL (liver type), is 0.5 under standard conditions but 1.0 on addition of 1% cardiolipin to the lipid mixture (asolectin). Low concentrations of palmitate (half-maximal effect at 0.5 mum), but not laurate, myristate, stearate, oleate, 1-hexadecanol, palmitoyl glycerol and palmitoyl CoA, decreased the H+/e(-) ratio in the presence of cardiolipin from 1.0 to 0.5, accompanied by an increase of coupled, but not of uncoupled respiration of proteoliposomes. Cardiolipin and palmitate did not influence the H+/e(-) stoichiometry and respiration of reconstituted cytochrome c oxidase from bovine heart, containing subunit VIaH (heart-type). The H+/e(-) stoichiometry of the heart enzyme, however, is decreased from 1.0 to 0.5 by 5 mm intraliposomal ATP (instead of 5 mm ADP). It is assumed that palmitate binds to subunit VIaL. The partial uncoupling of proton pumping in cytochrome c oxidase is suggested to participate in mammalian thermogenesis.