Separation, properties, and regulation of acyl coenzyme A dehydrogenases from bovine heart and liver

Abstract

A simple two-step procedure has been developed for the separation of bovine liver butyryl-CoA dehydrogenase (EC 1.3.99.2), medium chain acyl-CoA dehydrogenase (EC 1.3.99.3), which is most active with octanoyl-CoA as a substrate, and long-chain acyl-CoA dehydrogenase (EC 1.3.99.3) which acts preferentially on dodecanoyl-CoA. The same method was used for separating the acyl-CoA dehydrogenases present in bovine heart. Three acyl-CoA dehydrogenases were thus identified and found to be identical with the bovine liver enzymes as judged by their chromatographic behaviors, chain length specificities, and kinetic properties. Medium-chain and long-chain acyl-CoA dehydrogenases are active with a wide range of substrates from butyryl-CoA to stearoyl-CoA. However, their chain length specificities are clearly different from each other although insufficiently so to draw a firm conclusion regarding their physiological functions. The effects of mitochondrial coenzymes and metabolites, including intermediates of β oxidation, on the activities of the bovine acyl-CoA dehydrogenases, were investigated. Most noteworthy are the inhibitions of butyryl-CoA dehydrogenase by acetoacetyl-CoA ( K I = 10 −6 M) and of medium-chain and long-chain acyl-CoA dehydrogenases by 3-ketodecanoyl-CoA. The K I values for 3-ketodecanoyl-CoA with medium-chain and long-chain acyl-CoA dehydrogenases were found to be 8 × 10 −7 and 7.5 × 10 −8 m, respectively. We propose that the rate of fatty acid oxidation in heart is tuned to the energy demand of the tissue by a sequence of feedback controls which include the regulation of acyl-CoA dehydrogenases by 3-ketoacyl-CoA compounds.