POSSIBLE ROLE OF THE MITOCHONDRIAL OUTER-MEMBRANE IN REGULATION OF OXIDATIVE-PHOSPHORYLATION IN LIVING CELLS

This work shows for the first time that the outer mitochondrial membrane in vivo has low permeability to ADP and can control its diffusion in cells. In saponin-skinned preparations of skeletal muscle or myocardium, cell respiration can be maximally activated only by millimolar concentrations of ADP. The apparent K(m) values are 297 +/- 35 and 334 +/- 54 muM, respectively. Full extraction of myosin with 0.8 M KCl left intact the structure of mitochondria and produced no significant change in the apparent K(m) for external ADP. However, destruction of the mitochondrial external membrane by osmotic shock (treatment with 40 mosM KCl) decreased the apparent K(m) to 323 +/- 5.0 muM. In isolated mitochondria, K(m) was 17.6 +/- 1.0 muM. The data suggest the existence of an intracellular factor whose function in living cells is to control the movement of ADP across the mitochondrial outer membrane. This factor is lost during isolation of mitochondria. On the activation of mitochondrial creatine kinase, the weak intracellular ADP fluxes crossing the mitochondrial outer membrane are considerably amplified because of the tight coupling between mitochondrial creatine kinase and the system of oxidative phosphorylation.