Interaction of a cytoplasmic factor with electron and ion transfer coupled functions of mitochondria

Intramitochondrial Mg 2+ is labilized by uncouplers of oxidative phosphorylation or by valinomycin. This effect of uncouplers and of valinomycin exhibits ADP dependence, while the Mg 2+ labilizing action of valinomycin requires K + also. A trace amount (∼ 10 −6 M) of a purified cytoplasmic factor (CMF) prevents the induction of mitochondrial Mg 2+ ejection by both uncouplers and valinomycin and simultaneously activates mitochondrial metabolism. Oxidizable substrates protect mitochondrial Mg 2+ in a transient manner against labilization by uncouplers but not against valinomycin. It is concluded that the CMF-sensitive bound Mg 2+ containing system of mitochondria regulates energy coupled electron and K + transfer as an energy transducer.