Oxidation of leucine by rat skeletal muscle.

ODESSEY, RICHARD, AND ALFRED L. GOLDBERG. Oxidation of leucine by rat skeletal muscle. Am. J. Physiol. 223(6) : 1376-1383. 1972.-In the isolated rat diaphragm, 14C02 production from L-leucine-1 -14C occurred at 86 y0 of the rate of its incorporation into protein. Experiments with L-leucine-U-14C indicate complete oxidation of leucine under these conditions. 14C02 production from leucine-1-14C was inhibited slightly by glucose (15 %) but not by acetate, pyruvate, P-hydroxbutyrate, or palmitate. Amino acids at plasma concentrations inhibited 14C02 production (3O40 (r,) without affecting protein synthesis. Cycloheximide blocked incorporation into protein but stimulated 14C02 production, whereas cyanide and iodoacetate inhibited both processes. Addition of ouabain or the removal of Na+ from the incubation medium inhibited incorporation into protein but not oxidation. Appreciable oxidation of leucine also occurred in the dark soleus and the pale extensor digitorum longus muscles. The diaphragm catabolized leucine at rates similar to liver slices but severalfold less actively than epidydimal fat pad or kidney and brain slices. Since skeletal muscle accounts for over 400/, of the body mass, muscle is probably the major site of leucine catabolism in the animal.