THE SUCCINIC OXIDASE ACTIVITY OF RAT LIVER MITOCHONDRIA

Abstract

Rat liver mitochondria diluted into a high-potassium phosphate-free medium containing 2 × 10⁻⁵ M DNP take up oxygen readily if succinate is added at the same time as the mitochondria. If the addition of succinate is delayed, the respiration elicited is markedly reduced, falling to about 5% of the zero-time control at 2 minutes. Succinate-linked respiration can be restored by the addition of ATP or of cysteine sulphinic acid. A spontaneous recovery occurs on prolonged incubation (> 20 minutes). The inactivation, at least at such short incubation times, is dependent on the presence of DNP, and partial protection is provided by inorganic phosphate and the substitution of sucrose for KCl. Considerable protection is also provided by the presence of 1.5 mM Amytal. These results are all consistent with the hypothesis that oxaloacetate is produced from endogenous substrate during the first 1 or 2 minutes after dilution of the mitochondria, and that the failure to demonstrate succinic oxidase activity after this time is due to the inhibition of succinic dehydrogenase by oxaloacetate.