Purification and properties of rat D-3-hydroxyacyl-CoA dehydratase: D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein.

We have previously purified two D-3-hydroxyacyl-CoA dehydratase preparations from human liver. One preparation contained a 77-kDa polypeptide and smaller polypeptides, and the other was a homodimer of a 46-kDa polypeptide. Three different purified rat peroxisomal D-3-hydroxyacyl-CoA dehydratase preparations have been reported. Therefore, rat enzyme was purified in this study to confirm the enzyme structure. Two preparations with similar molecular structures to the human enzyme preparations were obtained, and these were similar to each other in immunochemical and catalytic properties. It was suggested that the native enzyme was a homodimer of the 77-kDa polypeptide, and this enzyme was modified to a homodimer of the 46-kDa polypeptide, because conversion of the 77-kDa polypeptide to smaller polypeptides including the 46-kDa polypeptide was clearly observed during purification. Rat liver subcellular fractionation study indicates that this enzyme is located in peroxisomes. The enzyme preparation containing the 77-kDa polypeptide catalyzed the D-3-hydroxyacyl-CoA dehydrogenase reaction as well as the dehydratase reaction. Thus, it is proposed that this enzyme is D-3-hydroxyacyl-CoA dehydratase/ D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein.