ATP Synthase K + - and H + -Fluxes Drive ATP Synthesis and Enable Mitochondrial K + -"Uniporter" Function: I. Characterization of Ion Fluxes.

ATP synthase (F 1 F o ) synthesizes daily our body's weight in ATP, whose production-rate can be transiently increased several-fold to meet changes in energy utilization. Using purified mammalian F 1 F o -reconstituted proteoliposomes and isolated mitochondria, we show F 1 F o can utilize both ΔΨ m -driven H + - and K + -transport to synthesize ATP under physiological pH = 7.2 and K + = 140 mEq/L conditions. Purely K + -driven ATP synthesis from single F 1 F o molecules measured by bioluminescence photon detection could be directly demonstrated along with simultaneous measurements of unitary K + currents by voltage clamp, both blocked by specific F o inhibitors. In the presence of K + , compared to osmotically-matched conditions in which this cation is absent, isolated mitochondria display 3.5-fold higher rates of ATP synthesis, at the expense of 2.6-fold higher rates of oxygen consumption, these fluxes being driven by a 2.7:1 K + : H + stoichiometry. The excellent agreement between the functional data obtained from purified F 1 F o single molecule experiments and ATP synthase studied in the intact mitochondrion under unaltered OxPhos coupling by K + presence, is entirely consistent with K + transport through the ATP synthase driving the observed increase in ATP synthesis. Thus, both K + (harnessing ΔΨ m ) and H + (harnessing its chemical potential energy, Δμ H ) drive ATP generation during normal physiology.