Two 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-hydroxyacyl-CoA dehydrogenase reaction: mitochondrial monofunctional 3-hydroxyacly-CoA dehydrogenase, mitochondrial enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase trifunctional protein, and peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein. The presence of isozymes of monofunctional 3-hydroxyacyl-CoA dehydrogenase was not known. In the present study, two monofunctional mitochondrial 3-hydroxyacyl-CoA dehydrogenases were purified from bovine liver. Type I enzyme was composed of two identical subunits with molecular mass of 35 kDa, and type II enzyme was a homotetramer 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 classical enzyme purified from various tissues, but type II enzyme was concluded to be a new enzyme. Type I enzyme was ubiquitous, but type II enzyme was rich in bovine and sheep, of several animal livers so far examined.