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

ATP synthase (FF) 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 FF-reconstituted proteoliposomes and isolated mitochondria, we show FF can utilize both ΔΨ-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 FF 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 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 FF 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, K (harnessing ΔΨ) and H (harnessing its chemical potential energy, Δμ) drive ATP generation during normal physiology.