Regulation of the H⁺/e⁻ stoichiometry of cytochrome c oxidase from bovine heart by intramitochondrial ATP/ADP ratios

This paper describes the effect of intramitochondrial ATP/ADP ratios on the H+/e- stoichiometry of reconstituted cytochrome c oxidase (COX) from bovine heart. At 100% intraliposomal ATP the H+/e- stoichiometry of the reconstituted enzyme is decreased to half of the value measured below 98% intraliposomal ATP (above 2% ADP), while it remains constant up to 100% ADP. The decrease is obtained with different COX preparations, independent of the absolute value of the H+/e- stoichiometry. Decrease of H+/e- stoichiometry is prevented by preincubation of the enzyme with a tissue-specific monoclonal antibody to subunit VIa-H (heart type). Tissue-specific regulation of the efficiency of energy transduction in COX of muscle mitochondria could have a physiological function in maintaining the body temperature at rest or sleep, i.e. at low ATP expenditure.