Efficiency of oxidative phosphorylation during the oxidation of pyruvate

Abstract

The phosphorylation quotient, equivalents of organic phosphate formed atoms of O2 consumed associated with the oxidation of pyruvate by suspensions of washed subcellular particles of kidney cortex was calculated from measurements of the rate of incorporation of p32 into adenosinetriphosphate. When pyruvate, in the presence of bicarbonate, was completely oxidized (as indicated by an O2/pyruvate ratio of 2.5) the avg. phosphorylation quotient was 2.23 (range 2.08-2.6). When pyruvate was incompletely oxidized phosphorylation quotients up to 3.92 were obtained. From the regression line obtained by plotting phosphorylation quotients against the O2/pyruvate ratio, a phosphorylation quotient of 4 was obtained for the oxidation of pyruvate to acetate. Either bicarbonate, oxaloacetate or a precursor of oxaloacetate must be present if pyruvate is to be oxidized beyond acetate. The avg. phosphorylation quotient in the presence of fumarate (1.7) or oxaloacetate (2.13) was lower than that obtained with bicarbonate. Unfractionated suspensions completely oxidizing pyruvate gave a phosphorylation quotient of 1.3. Reasons for phosphorylation quotients below the expected value of 3 are considered. In presence of 0.001 M-fumarate or oxaloacetate, pyruvate (0.0025 M)was oxidized beyond the stage of acetate (O2/pyruvate ratio greater than 0.5) but was not completely oxidized. At pH 7.8, a P-containing compound other than adenosinetriphosphate or orthophosphate, probably pyrophosphate, was formed.