Metabolic network control of oxidative phosphorylation - Multiple roles of inorganic phosphate

Phosphate (P-i) is a putative cytosolic signaling molecule in the regulation of oxidative phosphorylation. Here, by using a multiparameter monitoring system, we show that P-i controls oxidative phosphorylation in a balanced fashion, modulating both the generation of useful potential energy and the formation of ATP by F1F0-ATPase in heart and skeletal muscle mitochondria. In these studies the effect of P-i was determined on the mitochondria [NADH], NADH generating capacity, matrix pH, membrane potential, oxygen consumption, and cytochrome reduction level. P-i enhanced NADH generation and was obligatory for electron flow under uncoupled conditions. P-i oxidized cytochrome b (cyto-b) and reduced cytochrome c (cyto-c), potentially improving the coupling between the NADH free energy and the proton motive force. The apparent limitation in reducing equivalent flow between cyto-b and cyto-c in the absence of P-i was confirmed in the intact heart by using optical spectroscopic techniques under conditions with low cytosolic [P-i]. These results demonstrate that P-i signaling results in the balanced modulation of oxidative phosphorylation, by influencing both DeltaG(H+) generation and ATP production, which may contribute to the energy metabolism homeostasis observed in intact systems.