Carnitine acyltransferase and acyl-coenzyme A hydrolase activities in human liver. Quantitative analysis of their subcellular localization

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Abstract
The subcellular localizations of carnitine acyltransferase and acyl CoA hydrolase activities with different chain-length substrates were quantitatively evaluated in human liver by fractionation of total homogenates in metrizamide density gradients and by differential centrifugation. Peroxisomes contain 8-37% of the liver acyltransferase activity, the relative amount depending on the chain length of the substrate. The remaining activity was ascribed to mitochondria, except for carnitine octanoyltransferase, for which 25% of the activity was present in microsomal fractions. In contrast with rat liver, where the activity in peroxisomes is very low or absent, human liver peroxisomes contain about 20% of the carnitine palmitoyltransferase. Short-chain acyl CoA hydrolase activity was localized mainly in the mitochondrial and soluble compartments; the long-chain activity was present in both microsomal fractions and the soluble compartment. Particle-bound acyl CoA hydrolase activity for medium-chain substrates exhibited an intermediate distribution, in mictochondria and microsomal fractions, with 30-40% of the activity in the soluble fraction. No acyl CoA hydrolase activity appears to be present in human liver peroxisomes.