Abstract
To elucidate feedback control of oxidative phosphorylation by products of ATP hydrolysis and the underlying time hierarchy, the response of cardiac mitochondria oxidizing pyruvate to steady states in [ATP], [ADP] and inorganic phosphate ([Pi]) was characterized. A range of steady states in [ATP], [ADP] in the neighborhood of 1 mM and 5 mM [Pi] were achieved in a cardiac mitochondrial preparation and the rate of respiration, the fraction of nicotine adenine dinucleotide pool in the reduced state, the fraction of cytochrome c pool in the reduced state and the inner membrane potential were measured. Evolution of the steady states of the measured variables with the flux of respiration shows that, a) a higher phosphorylation potential is achieved by mitochondria at 5 mM [P] than at 1 mM [P] for a given flux of respiration, b) F F ATPase is the fastest responding component of the OxPhos system followed by the electron transport chain and substrate dehydrogenation systems in increasing order of response times, c) based on the above time hierarchy, applying a near equilibrium 0 approximation to F1FoATPase shows that a putative feedback signal for 0 the overall substrate dehydrogenation flux could be matrix [ADP]×[Pi]/[ATP] but not [ADP]/[ATP] by itself, and d) contrary to previous models of regulation of oxidative phosphorylation, [Pi] does not modulate the activity of complex III.