Fig. 1. The critical role of acetyl-CoA in oxidative metabolism. Both glucose and fatty acids yield acetyl-CoA which can enter the tricarboxylic acid cycle for complete oxidation. Pyruvate generated by glycolysis () from glucose generates acetyl-CoA via pyruvate dehydrogenase (). If acetyl-CoA generation exceeds utilization in the tricarboxylic acid cycle, acetyl-CoA will accumulate and can inhibit pyruvate dehydrogenase ( – – – in figure). Pyruvate will be converted to lactate if pyruvate dehydrogenase activity is inadequate. The removal of the acetyl group as acetylcarnitine via carnitine acetyltransferase () can remove this inhibition and produce an alternative product of oxidation. The net production of acetylcarnitine can only be sustained for very brief periods in human muscle.