Bacitracin is a proteolytic inhibitor which interacts with the intracellular processing of insulin. Its effects on pyruvate, fatty acid and amino acid metabolism were examined in rat hepatocyte suspensions. Bacitracin (0.25-1.0 mM) increased the oxidation of [1-14C]pyruvate by 50-70% and presumably therefore increased the flux through pyruvate dehydrogenase. This was found both in the presence of extracellular Ca2+ and in its absence, but not in the presence of 2 mM-2-chloropropionate, which inhibits pyruvate dehydrogenase kinase. Insulin did not further stimulate [1-14C]pyruvate oxidation in the presence of 1 mM-bacitracin. Bacitracin decreased 14CO2 formation from [2-14C]pyruvate (20-40%) and [U-14C]palmitate (30-70%), suggesting a decreased flux through the tricarboxylic acid cycle. Fatty acid oxidation before acetyl-CoA formation was also decreased. Bacitracin decreased the incorporation of label from [3H]leucine into protein in the absence of insulin, but not in its presence. Bacitracin is commonly used in studies on insulin action. Our results suggest that in such studies the effects noted may be related not only to an interaction of bacitracin with the intracellular processing of insulin but also to direct metabolic effects of bacitracin independent of insulin.

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