The subcellular distribution of the enzymes of the fatty acyl-CoA β-oxidation system, and the effects of di-(2-ethylhexyl)phthalate (DEHP) administration on their activities were studied in rat liver. The activities of enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase, and 3-ketoacyl-CoA thiolase were assayed using the acyl-CoAs having 4-, 8-, and 16-carbon acyl chains.The activities of cyanide-insensitive palmitoyl-CoA oxidation and acyl-CoA oxidase, which were localized in peroxisomes, were induced by DEHP treatment. The activity of acyl-CoA oxidase was approximately the same as that of palmitoyl-CoA oxidation and was much lower than those of other enzymes of β-oxidation.All of the activities of enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase, and 3-ketoacyl-CoA thiolase in liver homogenate were elevated by DEHP treatment. The extents of the increases in the activities were larger when longer chain length substrates were used, especially in the cases of the latter two enzymes.In the control group, the above three enzymes were found solely in mitochondria. In the DE1-II group, in contrast, high activities were found in peroxisomes as well as in mitochondria, except in the case of thiolase activity toward acetoacetyl-CoA. This activity and acetoacetyl pantetheine reducing activity, which is attributable to 3-hydroxyacyl-CoA dehydrogenase, were detected exclusively in mitochondria both in the control and in the DEHP groups.It appears that different 3-hydroxyacyl-CoA dehydrogenases and 3-ketoacyl-CoA thiolases are located in mitochondria and peroxisomes, and their activities in both fractions are induced by DEHP administration. © 1979 By The Journal Of Biochemistry.
