The phosphate potential maintained by mitochondria in State 4 is proportional to the proton-motive force

AbstractEvidence is presented for a proportional relationship between the extramitochondrial phosphate potential (ΔGexp) and the proton-motive force (Δ\̃gmH+) across the mitochondrial membrane in rat-liver mitochondria oxidising succinate in State 4, when Δ\̃gmH+ is varied by addition of uncouplers or malonate. This relationship was found when precautions were taken to minimise interference with the determination of ΔGpex and Δ\̃gmH+ by intramitochondrial nucleotides, adenylate kinase activity, the quenching method, and Δ\̃gmH+-dependent changes in matrix volume. A non-proportional ΔGpex/Δ\̃gmH+ relationship was obtained when these precautions were omitted. Our results do not support mosaic protonic coupling, but are not necessarily in conflict with other localised coupling schemes