Abstract
Phosphopyruvate is formed by washed, sheep-kidney particles during oxidation of alpha-oxoglutarate, succinate, fumarate, malate, oxaloacetate, and pyruvate plus bicarbonate; it is not formed during oxidation of pyruvate alone. Phosphate esters other than phosphopyruvate are formed during the later stages of incubation. After short periods the specific activity of phosphopyruvate is lower than that of phosphate. The data exclude phosphate, and suggest adenosine triphosphate as the immediate precursor of the phosphate group of phosphopyruvate. The observations that phosphopyruvate rapidly reaches isotopic equilibrium with added P32O43- and that added phosphopyruvate is rapidly removed indicates that turnover rate of phosphopyruvate is high. The mechanism of formation of phosphopyruvate is discussed.