Participation of inorganic phosphate in the chemiosmotic mechanism of mitochondrial energy transduction.

In respiring liver mitochondria in which Pi transport was inhibited and the intramitochondrial Pi value manipulated to vary about 3-fold, K+-ion uptake, H+-ion extrusion and stimulation of respiration were linearly related to the intramitochondrial Pi content. It is suggested that the HPO 2(4)-anion generated during respiration is the nondiffusible anion required for the Donnan distribution and membrane potential in mitochondria. The intramitochondrial H X HPO4-ionic species is the proton donor required for coupled respiration. The electroneural Pi-H+ cotransport closes the proton cycling in respiration.