CHARACTERISTICS OF MITOCHONDRIAL PROTON LEAK AND CONTROL OF OXIDATIVE-PHOSPHORYLATION IN THE MAJOR OXYGEN-CONSUMING TISSUES OF THE RAT

Maintenance of an electrochemical proton gradient across the mitochond rial inner membrane against the significant proton permeability of the membrane accounts for 25-30% of resting oxygen consumption in hepatoc ytes. It has been proposed that proton leak could be a significant con tributor to resting metabolic rate in mammals if it were present in ot her tissues. Mitochondria were isolated from the major oxygen-consumin g tissues (liver, kidney, brain and skeletal muscle) of the rat. In ea ch tissue, the mitochondria showed significant proton leak with the sa me characteristic non-linear dependence on membrane potential. Liver a nd kidney mitochondria showed similar membrane proton permeability per mg of mitochondrial protein; brain and muscle permeabilities were gre ater when expressed in this way. Differences in the kinetic response o f the substrate oxidation and phosphorylating systems to membrane pote ntial were observed. The substrate oxidation system was more active in kidney, brain and skeletal muscle mitochondria than in liver mitochon dria per mg of mitochondrial protein. Liver and kidney phosphorylating systems were less active than brain and skeletal muscle per mg of mit ochondrial protein. The control of oxidative phosphorylation was also assessed. The distribution of control in mitochondria isolated from th e four tissue types was found to be similar.