The large subunit of the pig heart mitochondrial membrane-bound β-oxidation complex is a long-chain enoyl-CoA hydratase: 3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme

The subunit locations of the component enzymes of the pig heart trifunctional mitochondrial β-oxidation complex are suggested by analyzing the primary structure of the large subunit of this membrane-bound multienzyme complex [Yang S.-Y.et al. (1994) Biochem. biophys. Res. Commun. 198, 431–437] with those of the subunits of the E. coli fatty acid oxidation complex and the corresponding mitochondrial matrix β-oxidation enzymes. Long-chain enoyl-CoA hydratase and long-chain 3-hydroxyacyl-CoA dehydrogenase are located in the amino-terminal and the central regions of the 79 kDa polypeptide, respectively, whereas the long-chain 3-ketoacyl-CoA thiolase is associated with the 46 kDa subunit of this complex. The pig heart mitochondrial bifunctional β-oxidation enzyme is more homologous to the large subunit of the prokaryotic fatty acid oxidation complex than to the peroxisomal trifunctional β-oxidation enzyme. The evolutionary trees of 3-hydroxyacyl-CoA dehydrogenases and enoyl-CoA hydratases suggest that the mitochondrial inner membrane-bound bifunctional β-oxidation enzyme and the corresponding matrix monofunctional β-oxidation enzymes are more remotely related to each other than to their corresponding prokaryotic enzymes, and that the genes of E. coli multifunctional fatty acid oxidation protein and pig heart mitochondrial bifunctional β-oxidation enzyme diverged after the appearance of eukaryotic cells.