Inhibition by anions of dinitrophenol-induced ATPase of mitochondria

Abstract

1. Succinate inhibits the dinitrophenol-induced ATPase of rat-liver mitochondria without having any effect on the redox state of the NAD(P). Cyanide, on the other hand, causes an increased reduction of NAD(P), without having any effect on the ATPase activity, provided that the latter is measured over a short period with a high concentration of mitochondria. Anaerobiosis also has no effect on the ATPase under these conditions. 2. There appear to be two reasons why succinate inhibits. In the first place it provides substrate for oxidative phosphorylation. However, even when oxidative phosphorylation is inhibited by antimycin, there is a residual inhibition that is largely competitive with dinitrophenol. 3. The non-oxidizable anion malonate also inhibits competitively in the absence of antimycin and partly competitively in its presence. 4. Inhibition by the dibasic acid anions malonate and d-malate separately is about the same and no further inhibition is obtained by the addition of two anions together. The tribasic acid anion tricarballylate also inhibits and its effect is additive to that of malonate or d-malate. Further inhibition is obtained when acetate and aspartate are added in addition to malonate and tricarballylate. 5. The dinitrophenol-induced ATPase of house-fly mitochondria is not inhibited by succinate, α-oxoglutarate, isocitrate or l-malate, which are not oxidized by these mitochondria. It is also not inhibited by l-glutamate, d-malate or lactate, but is inhibited by acetate, malonate, l-aspartate, pyruvate and, especially, by tricarballylate. 6. The inhibitory effects of anions can be explained by competition with dinitrophenol for penetration of the mitochondrial matrix. It is proposed that dinitrophenol may enter the mitochondria via a number of carrier systems specific for different types of anion.