2 MITOCHONDRIAL 3-HYDROXYACYL-COA DEHYDROGENASES IN BOVINE LIVER

3-Hydroxyacyl-CoA dehydrogenase catalyzes the third reaction of fatty acid beta-oxidation spiral, There are three enzymes catalyzing the 3-h ydroxyacyl-CoA dehydrogenase reaction: mitochondrial monofunctional 3- hydroxyacly-CoA dehydrogenase, mitochondrial enoyl-CoA hydratase/3-hyd roxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase trifunctional prote in, and peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenas e bifunctional protein. The presence of isozymes of monofunctional 3-h ydroxyacyl-CoA dehydrogenase was not known. In the present study, two monofunctional mitochondrial 3-hydroxyacyl-CoA dehydrogenases were pur ified from bovine liver. Type I enzyme was composed of two identical s ubunits with molecular mass of 35 kDa, and type II enzyme was a homote tramer of a 28 kDa polypeptide. In respect to the molecular structures , immunochemical properties, and carbon chain length specificities of acyl-CoA substrates, type I enzyme was the same as the well-known clas sical enzyme purified from various tissues, but type II enzyme was con cluded to be a new enzyme. Type I enzyme was ubiquitous, but type II e nzyme was rich in bovine and sheep, of several animal livers so far ex amined.