Physiological role of D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein.
The second and third reactions of the peroxisomal beta-oxidation spiral are thought to be catalyzed by enoyl-CoA hydratase/L-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (L-bifunctional protein). Recently, we found the presence of D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (D-bifunctional protein) in mammalian peroxisomes. Therefore, we studied the physiological role of the D-bifunctional protein. The contents of the L- and D-bifunctional proteins were about 0.01 and 0.5 microg/mg protein, respectively, in cultured human skin fibroblasts. The activity of conversion of hexadecenoyl-CoA to 3-ketopalmitoyl-CoA by the D-bifunctional protein was estimated to be about 0.5 milliunit/mg of fibroblast protein. This value was about 100-fold that of the L-bifunctional protein in the fibroblasts. From comparison of the activities of the bifunctional proteins with the rate of palmitate oxidation and the activities of acyl-CoA oxidase and 3-ketoacyl-CoA thiolase, it is proposed that the D-bifunctional protein plays a major role in the peroxisomal oxidation of palmitate in the fibroblasts. The contents of both the L- and D-bifunctional proteins in liver were about 2.5 microg/mg protein. Therefore, it is suggested that the D-bifunctional protein also plays a significant role in human liver peroxisomal fatty acid oxidation. Actions of the bifunctional proteins on enoyl forms of other acyl-CoA derivatives were examined. The D-bifunctional protein but not the L-bifunctional protein reacted with 2-methylhexadecenoyl-CoA and 3alpha,7alpha,12alpha-trihydroxy-5beta-cholest-2 4-enoyl-CoA. We propose that, among the reactions of the distinct group of carboxylates oxidized specifically in peroxisomes, oxidation of 2-methyl-branched fatty acids and side-chain shortening of cholesterol for bile acid formation are catalyzed by the D-bifunctional protein, but not the L-bifunctional protein.
Jiang
L L
LL
Department of Biochemistry, Shinshu University School of Medicine, Matsumoto, Nagano.
Kurosawa
T
T
Sato
M
M
Suzuki
Y
Y
Hashimoto
T
T
D015067:17-Hydroxysteroid Dehydrogenases; D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000378:metabolism*; D002478:Cells, Cultured; D003065:Coenzyme A / Q000378:metabolism; D004746:Enoyl-CoA Hydratase; D006801:Humans; D006836:Hydro-Lyases / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism*; D064029:Peroxisomal Multifunctional Protein-2; D014407:Tumor Cells, Cultured
D009097:Multienzyme Complexes; D015067:17-Hydroxysteroid Dehydrogenases; D015094:3-Hydroxyacyl CoA Dehydrogenases; D006836:Hydro-Lyases; D064029:Peroxisomal Multifunctional Protein-2; C104587:HSD17B4 protein, human; D004746:Enoyl-CoA Hydratase; D003065:Coenzyme A