Inhibition of adenosine triphosphatase and respiration of rat-liver mitochondria by dinitrophenols

1. The stimulating and inhibitory effect of nitrophenols on various mitochondrial systems are compared. Both respiration and ATPase are stimulated by low dinitrophenol concentrations followed by inhibition at higher concentrations. The concentration of dinitrophenol inducing maximal activity (copt) differs for ATPase, pyruvate oxidation, β-hydroxybutyrate oxidation and succinate oxidation. 2. It is concluded that dinitrophenols have a specific inhibitory action on the uncoupled respiration and on the ATPase of intact rat-liver mitochondria. This inhibition can be located between NADH and flavoprotein and between flavoprotein and cytochrome c. Although the third phosphorylating step is as easily uncoupled as the other two steps, no inhibition of this step by uncoupling agents occurs. 3. The inhibition by alkyldinitrophenols can be reversed by lowering the partition coefficient of the inhibitor between the mitochondrial lipid and the medium. 4. From the fact that a difference exists between copt for ATPaase and for NAD-linked respiration it can be concluded that dinitrophenols act by hydrolysing a high-energy intermediate rather than by allowing respiration to proceed without the formation of a high-energy intermediate