[Local coupling of respiration processes and phosphorylation in rat liver mitochondria]

One variant of the model of the local coupling of phosphorylation and respiration in intact mitochondria was experimentally verified. The model is based on the following postulates: (1). Upon the functioning of H+ pumps, hydrogen ions bound to the outer membrane surface do not enter the aqueous phase but are utilized for ATP synthesis in the membrane supercomplex respiratory H+ pump--ATP synthetase. (2). During the functioning of H+ pumps, an appreciable part of the energy of oxidation reactions can be stored in the form of the thermodynamic (solvation) potential of H+ ions bound to the outer membrane surface. According to the model, the hydration of hydrogen ions during the transition from the outer face of the inner membrane to the aqueous phase should lead to a decrease in the efficiency of the system of the coupling of respiration and phosphorylation. The model takes into account the ability of the nonpermeating buffer to catalyze the detachment of hydrogen ions from the membrane surface to the aqueous phase and provide their complete solvation. A preparation of phosphorylating mitochondria with the covalently bound pH probe was obtained. This made it possible to register for the first time the presence of a local H+ gradient on the outer side of the inner mitochondrial membrane during the stable functioning of the oxidative phosphorylation system. It was shown on these mitochondrial preparations that a decrease in the outer local H+ gradient by the action of increased concentrations of buffer is accompanied by a significant decrease in the ADP/O parameter and a partial dissociation of oxidative phosphorylation. Conditions were determined under which increased concentrations of buffer in the incubation medium cause a partial dissociation and a decrease in the ADP/O value from 20% to twofold (depending on the quality of mitochondrial preparations). The results obtained are in full agreement with the predictions of the model.