l-carnitine acyltransferase in intact peroxisomes is inhibited by malonyl-CoA

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Abstract
Inhibition of the overt mitochondrial carnitine palmitoyltransferase by malonyl-CoA is important in the regulation of fatty acid oxidation. In the past, the contribution of peroxisomal carnitine acyltransferase activity of the generation of medium- and long-chain acylcarnitines in the cytoplasm has been ignored. On the basis of marker enzyme levels, we now estimate that peroxisomal palmitoyltransferase activity constitutes about 20% of the peroxisomal plus overt-mitochondrial pool in fed rat liver. When assayed in situ, both the palmitoytransferase decanoyltransferase activities of gradient-purified peroxisomes are sensitive to malonyl-CoA, with up to 90% inhibition reached at ess than 10 .mu.M-malonyl-CoA. Very similar results were obtained with intact gradient-purified mitochondria from the same livers. In addition, the acyl-CoA substrate chain-length specificity was identical in both the perioxisomes and the mitochondria, with a decanoyltransferase/palmitoyltransferase ration of 2. Thus the overt carnitine acyltransferase activites in peroxisomes and mitochondria have the same properties. Further, the malonyl-CoA sensitivity of the peroxisomal activity is lost on solubilization, as has been observed for the overt mitochondrial enzyme. It is suggested that malyonyl-CoA inhibition of the peroxisomal enzyme as well as of the mitochondrial enzyme is important for the regulation of mitochondrial fatty acid oxidation.

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