The effect of dinitrophenol and amytal on the reduction of acetoacetate in the presence of succinate

Abstract

DNP at high concentrations (0.5 m[image]) inhibits the O2 uptake of liver homogenates in the presence of succinate. It also inhibits the removal of succinate and this inhibition was greater than that of the O2 uptake. At a concentration of 0.05 m[image] DNP increased the rate of the O2 uptake without increasing the rate of succinate removal. Thus DNP shifts the substrate of oxidation from succinate towards other substances. Amytal when added together with DNP abolished the following effects of DNP (a) the stimulation of the O2 consumption at 0.05 m[image]-DNP; (b) the inhibition of the O2 uptake at 0.5 m[image]-DNP; (c) the inhibition of the reduction of acetoacetate at both DNP concentrations; (d) the inhibition of succinate oxidation at 0.5 m[image]-DNP. It did not remove the inhibition of oxidative phosphorylation by DNP. The stimulation of respiration caused by Amytal in the presence of 0.5 m[image]-DNP was prevented by ATP. Thus ATP inhibited the O2 uptake in the presence of DNP plus Amytal but not in the absence of these substances. Liver mitochondria prepared in iso-osmotic sucrose solution reacted in the same way as homogenates towards DNP, Amytal and ATP. Mito- chondria prepared in saline media behaved differently. Homogenates of pigeon-breast muscle and sheep heart showed the same response as rat liver to DNP and Amytal. The fact that a reduction of acetoacetate to [beta]-hydroxybutyrate can readily occur in the presence of dinitrophenol and Amytal supports the view put forward previously that under the test conditions a reversal of oxidative phosphorylation does not play a major part in the reduction of acetoacetate.