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

Abstract

Evidence is presented for a proportional relationship between the extramitochondrial phosphate potential (ΔG ^ex _p) 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 ΔG _p ^ex and Δ _gmH+ by intramitochondrial nucleotides, adenylate kinase activity, the quenching method, and Δ _gmH+ -dependent changes in matrix volume. A non-proportional ΔG _p ^ex/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.