A rôle of nuclei in oxidative phosphorylation.

Isolated mitochondria will catalyze many of the oxidative reactions observed with intact cells. However, such enzymatic activity may be only an approximation of the in vivo metabolism. Metabolic studies of reconstituted cells have utilized washed residues which represent simultaneously isolated cellular components (l), the recombination of cellular components in vitro (2), and special media which approximate the intracellular concentration of cofactors and inorganic ions (3). Potter et al. observed that a whole homogenate of rat liver oxidized pyruvic and oxalacetic acids at a faster rate than did mitochondria alone. Further, the oxidative rate of mitochondria was stimulated by the addition of nuclear or supernatant fractions (2). These fractions alone showed no appreciable oxidation of the substrates. It was postulated that the rate of reaction was limited by the availability of phosphate acceptors. The ATPase activity of the nuclear and supernatant fractions accelerated the regeneration of the acceptors from adenosinetriphosphate (ATP). Similarly it has been shown that these oxidative processes of mitochondria are stimulated by the addition of hexokinase and glucose, which will also regenerate adenosinediphosphate (ADP) from ATP (4). In this report is described a stimulatory effect of nuclei on the rate of fixation of inorganic phosphate by mitochondria. This effect of nuclei is apart from that associated with the nuclear ATPase activity and also affects the oxidative rate.