Further Characterization of the Peroxisomal 3‐Hydroxyacyl‐Coa Dehydrogenases from Rat Liver

Abstract

Recently, we purified five 3-hydroxyacyl-CoA dehydrogenases from isolated rat liver peroxisomal fractions. The enzymes were designated I-V according to their order of elution from the first column used in the purification procedure. Determination of the substrate (L- or D-hydroxyacyl-CoA) stereo-specificity and (de)hydratase measurements with the different 3-hydroxyacyl-CoA stereoisomers of straight-chain fatty acids and the bile acid intermediate trihydroxycoprostanic acid, immunoblotting analysis with antibodies raised against the different enzymes and peptide sequencing, all performed on enzymes I-V and molecular cloning of enzyme III revealed the following picture. Rat liver peroxisomes contain two multifunctional beta-oxidation proteins: (a) multifunctional protein 1 (the classical multifunctional protein; MFP-1) displaying 2-enoyl-CoA hydratase, L-3-hydroxyacyl-CoA dehydrogenase and delta 3, delta 2-enoyl-CoA isomerase activity (enzyme IV) and (b) multifunctional protein 2 (MFP-2) displaying 2-enoyl-CoA hydratase and D-3-hydroxyacyl-CoA dehydrogenase activity (enzyme III). Because of their substrate stereospecificity and because of the stereochemical configuration of the naturally occurring beta-oxidation intermediates, MFP-1 and MFP-2 appear to be involved in the beta-oxidation of fatty acids and bile acids intermediates, respectively. The deduced amino acid sequence of the cloned MFP-2 cDNA is highly similar to that of the recently described porcine endometrial estradiol 17 beta-dehydrogenase [Leenders, F., Adamski, J., Husen, B., Thole, H. H. & Jungblut, P. W. (1994) Eur. J. Biochem. 222, 221-227]. In agreement, MFP-2 also displayed estradiol 17 beta-dehydrogenase activity, indicating that MFP-2 and the steroid dehydrogenase are identical enzymes. MFP-2 is partially cleaved, most probably in vivo, in a estradiol 17 beta-dehydrogenase/D-3-hydroxyacyl-CoA dehydrogenase that forms a dimeric complex (enzyme I) and a hydratase. The physiological significance of enzyme I in bile acid synthesis (and steroid metabolism) remains to be determined. MFP-1 (enzyme IV) is artefactually cleaved during purification giving rise to 3-hydroxyacyl-CoA dehydrogenase V. 3-Hydroxyacyl-CoA dehydrogenase II is a mitochondrial contaminant similar to porcine and murine mitochondrial 3-hydroxyacyl-CoA dehydrogenase.