Fig. 5: Mechanistic model of proton transport in the antiporter modules.

Schematic model of (a) antiporter-mediated proton transport. Blue/grey lines schematically show conneted/disconnected proton wires, and red dotted line an electrostatic repulsion. Blue/red/white circles – putative positive/negative/neutral protonation states. pKaA – pKa of N-side proton acceptor; pKaD – pKa of P-side proton donor; ΔGO→C – free energy closing ion pair; pHout – pH of N-side; pHin – pH of P-side. b Comparison of a proton pumping model in the intact Complex I.