On the oxidation of acetate and pyruvate by guinea-pig heart sarcosomes

Abstract

1. 1. Sarcosomes isolated from guinea-pig heart have been used in a comparative study of the mechanism of oxidation of pyruvate and acetate by these particles. 2. 2. Acetate oxidation, without added malate, is very rapid when the concentration of phosphate is low, but us strongly inhibited by higher phosphate concentrations. In the presence of concentrations of phosphate up to 30 mM, acetate is well oxidized when malate is also present. 3. 3. Acetate oxidation in the presence of 2,4-dinitrophenol is initiated on addition of ATP. Magnesium inhibits this oxidation and the inhibition is relieved by oligomycin. 4. 4. Pyruvate is rapidly oxidized in the absence of added citric acid cycle intermediates during the first minutes of incubation, the rate rapidly decreasing with time to near zero (3–10 min). Evidence is presented which strongly suggests that the supply of citric acid cycle intermediates is depleted during the oxidation of pyruvate. 5. 5. Carnitine has no effect on the oxidation of acetate or pyruvate in the citric acid cycle, but stimulates the oxidative decarboxylation of pyruvate, probably as a result of acetylcarnitine formation from pyruvate. 6. 6. Under the conditions of these experiments, pyruvate oxidation is decreased about 50% by an equimolar concentration of acetate.