Inhibition of palmitoylcarnitine oxidation by pyruvate in rat heart mitochondria.

The oxidation of 1-14C-palmitoylcarnitine by rat heart mitochondria has been measured by assessing both the disappearance of substrate and the appearance of labelled products. Pyruvate inhibited palmitoylcarnitine oxidation by about 40%. Fifty percent inhibition occurred at about 20 mumol/L pyruvate. The inhibitory effect of pyruvate required entry of pyruvate into mitochondria since it did not occur in the presence of alpha-cyano-4-hydroxycinnamic acid, an inhibitor of the mitochondrial pyruvate transporter. The inhibitory effect of pyruvate also required an active pyruvate dehydrogenase. These studies indicate a mechanism that may be important in the replacement of fatty acids by carbohydrate as fuels of respiration of the heart during the transition from the starved to the fed state.