Cytochrome P450 CYP27-catalyzed oxidation of C27-steroid into C27-acid.
Rabbit liver cytochrome P450 CYP27 has been previously shown to catalyze the complete conversion of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid. This study compares some properties of the reactions involved, the 27-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol and the further oxidation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,27-tetrol. The Km was the same for the two substrates, whereas the Vmax was three times higher for 27-hydroxylation than for the oxidation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,27-tetrol. Ketoconazole inhibited both reactions, whereas disulfiram did not. Carbon monoxide inhibited the 27-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol but not the further oxidation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,27-tetrol. There was no difference in sensitivity to varying oxygen concentrations between the two reactions. The present study shows that CYP27 also converts, although less efficiently, 5 beta-cholestane-3 alpha,7 alpha-diol into 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoic acid and cholesterol into 3 beta-hydroxy-5-cholestanoic acid. The rate of oxidation of cholesterol into C27-acid was very low--less than 1% of that with the other C27-steroids.
Betsholtz
I H
IH
Department of Pharmaceutical Biosciences, University of Uppsala, Sweden.
Wikvall
K
K
D000444:Aldehyde Dehydrogenase / Q000037:antagonists & inhibitors; D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology; D053493:Cholestanetriol 26-Monooxygenase; D002777:Cholestanols / Q000378:metabolism*; D002793:Cholic Acids / Q000096:biosynthesis*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004221:Disulfiram / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006900:Hydroxylation; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D008930:Mitochondria, Liver / Q000201:enzymology; D010084:Oxidation-Reduction; D011817:Rabbits; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D002777:Cholestanols; D002793:Cholic Acids; D065607:Cytochrome P-450 Enzyme Inhibitors; C009561:3,7,12-trihydroxycoprostane; D002248:Carbon Monoxide; C020262:cholestane-3,7,12,26-tetrol; C003681:3,7,12-trihydroxycoprostanic acid; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D053493:Cholestanetriol 26-Monooxygenase; D000444:Aldehyde Dehydrogenase; D007654:Ketoconazole; D004221:Disulfiram