The oxidation of pyruvate by heart muscle

Abstract

Minced heart muscle of the sheep used O2 and pyruvate at about the same rate as the intact dog''s heart. Both O2 consumption and pyruvate utilization are inhibited by malonate, an inhibition partially removed by fumarate. Each mol. of fumarate added causes removal of one extra mol. of pyruvate, and an extra consumption of 2 to 3 mol. of O2. Succinate is formed in amts. approximately equivalent to the added fumarate. Pyruvate in concs. up to 0.02 M maintains the respiration of the minced heart. Higher concs. inhibit O2 consumption; the pyruvate which disappears is incompletely oxidized, and citrate and [alpha]-ketoglutarate appear, the amts. being increased by the addition of fumarate. Added citrate disappears in presence of molecular O2 and also anaerobically in presence of oxaloacetate. All of the substances involved in the citric acid cycle, pyruvate, fumarate, succinate. citrate and [alpha]-ketoglutarate, increase the respiration of the heart. These observations support the view that pyruvate is oxidized in the heart by way of the citric acid cycle and they cannot be satisfactorily explained otherwise.