Proton/electron stoichiometry of mitochondrialbc 1 complex. Influence of pH and transmembrane δpH

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Abstract
The effect of pH and transmembrane δpH on the efficiency of the proton pump of the mitochondrialbc1 complex bothin situ and in the reconstituted state was studied. In both cases the H+/e− ratio for vectorial proton translocation by thebc1 complex respiring at the steady state, under conditions in which the transmembrane pH difference (δpH) represents the only component of the proton motive force (δp), was significantly lower than that measured under level flow conditions. The latter amounts, at neutral pH, to 1 (2 including the scalar H+ release). In the reconstituted system steady-state δpH was modulated by changing the intravesicular buffer as well as the intra/extra-liposomal pH. Under these conditions the H+/e− ratio varied inversely with the δpH. The data presented show that δpH exerts a critical control on the proton pump of thebc1 complex. Increasing the external pH above neutrality caused a decrease of the level flowH+/e− ratio. This effect is explained in terms of proton/electron linkage inb cytochromes.