Broad specificity of carnitine palmitoyltransferase II towards long-chain acyl-CoA beta-oxidation intermediates and its practical approach to the synthesis of various long-chain acylcarnitines.

Abstract

Long-chain fatty acid β-oxidation defects involving 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) or mitochondrial trifunctional protein (MTP) (Pollitt 1995) are characterized by abnormal urinary organic acids and specific plasma acylcarnitine profile during crises (Dorland et al 1995). The same atypical acylcarnitine esters have also been found in in vitro studies comprising the incubation of patient's cells (Nada et al 1995; Schaefer et al 1995) with long-chain fatty acids. An explanation for the finding of these abnormalities might be that the different acyl-CoA esters that accumulate within the mitochondrial matrix are exported to the cytosol in the acylcarnitine form. The mechanism associated with this process is unclear but may primarily involve carnitine palmitoyltransferase (CPT) II catalysing the conversion of the intramitochondrial long-chain acyl-CoA esters into the corresponding acylcarnitines followed by export from the mitochondria via the acylcarnitine/carnitine carrier. While studying the specificity of CPT towards palmitoyl-CoA and its β-oxidation intermediates, we found that CPT II accepts as substrates not only acyl-CoA esters but also 2,3-unsaturated, 3-hydroxy and 3-keto acyl-CoA esters. In the present paper we have made use of the reactivity of CPT II towards 3-hydroxy-palmitoyl-CoA to synthesize 3-hydroxypalmitoylcarnitine enzymatically. The synthesis of this compound and other 3-hydroxyacylcarnitines is important for the qualitative and quantitative analysis of the acylcarnitine profile in LCHAD and MTP deficiencies. These substances may also be useful for experiments directed towards solving the problems of the peculiar clinical findings in LCHAD deficiency.