Kinetic Equivalence of pH Difference (ΔPh) and Electrical Potential (Δψ) across Membrane in ATP Synthesis by Bacillus PS3 FOF1-ATP Synthase

Abstract

The ATP synthase is the key player of Mitchell's chemiosmotic theory, converting the energy of transmembrane proton flow into the high-energy bond between ADP and phosphate. The proton motive force that drives this reaction consists of two components, the pH difference (ΔpH) across the membrane and transmembrane electrical potential (Δψ). The two are considered thermodynamically equivalent, but kinetic equivalence in the actual ATP synthesis is not warranted and previous experimental results vary. Here we show that, in the thermophilic Bacillus PS3 ATP synthase that lacks an inhibitory domain of the e subunit, ΔpH imposed by acid-base transition and Δψ produced by valinomycin-mediated K+ diffusion potential contribute equally to the rate of ATP synthesis, within the experimental range examined (ΔpH −0.3 to 2.4, Δψ −30 to 140 mV, pH around the catalytic domain 8.0). Either ΔpH or Δψ alone can drive synthesis, even when the other slightly opposes.