MECHANISM OF INHIBITION BY UNCOUPLERS OF SUCCINATE OXIDATION IN ISOLATED MITOCHONDRIA

1. The inhibition by uncouplers of succinate oxidation in isolated rabbit-kidney mitochondria has been studied. 2. In the absence of rotenone, the oxidation of 10 mM succinate was inhibited by uncouplers. This inhibition could be prevented by adding glutamate, palmitoylcarnitine or ATP. Activation by ATP occurred in the presence of oligomycin but not of atractyloside. 3. In the presence of rotenone, the uncoupler dicoumarol inhibited the oxidation of succinate when the substrate concentration was 1 mM but not when it was 10 mM. ATP had no effect on the inhibited respiration. Removal of dicoumarol with albumin under conditions in which the mitochondria could subsequently become energized led to a restoration of succinate oxidation. 4. In the absence of rotenone and presence of uncoupler, the activation of respiration by ATP was accompanied by a decline in the level of oxaloacetate and by the formation of phosphoenolpyruvate. 5. In the absence of rotenone and presence of uncoupler, there was an inverse correlation between the rate of respiration and the level of oxaloacetate. The activation of respiration by ATP or palmitoylcarnitine was accompanied by a decline in the level of oxaloacetate. 6. The addition of phosphoenolpyruvate, CO2 and ADP to mitochondria in the presence of uncoupler and rotenone led to an inhibition of succinate oxidation, presumably due to oxaloacetate formation. 7. It is concluded that the inhibition by uncouplers of succinate oxidation in the absence of rotenone and at relatively high succinate concentrations is due to the formation of oxaloacetate. © 1969.