title: 25-Hydroxylation of vitamin D3 by a cytochrome P-450 from rabbit liver mitochondria.
abstract: A cytochrome P-450 catalysing 25-hydroxylation of vitamin D3 was purified from liver mitochondria of untreated rabbits. The enzyme fraction contained 9 nmol of cytochrome P-450/mg of protein and showed only one protein band with an apparent Mr of 52,000 upon SDS/polyacrylamide-gel electrophoresis. The preparation showed a single protein spot with an apparent isoelectric point of 7.8 and an Mr of approx. 52,000 upon two-dimensional isoelectric-focusing-polyacrylamide-gel electrophoresis. The purified cytochrome P-450 catalysed 25-hydroxylation of vitamin D3 up to 5000 times more efficiently than did the mitochondria. The cytochrome P-450 required both ferredoxin and ferredoxin reductase for catalytic activity. Microsomal NADPH-cytochrome P-450 reductase could not replace ferredoxin and ferredoxin reductase. The cytochrome P-450 catalysed, in addition to 25-hydroxylation of vitamin D3, the 25-hydroxylation of 1 alpha-hydroxyvitamin D3 and the 26-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. The enzyme did not catalyse side-chain cleavage of cholesterol, 11 beta-hydroxylation of deoxycorticosterone, 1 alpha-hydroxylation of 25-hydroxyvitamin D3, hydroxylations of lauric acid and testosterone or demethylation of benzphetamine. The results raise the possibility that the 25-hydroxylation of vitamin D3 and the 26-hydroxylation of C27 steroids are catalysed by the same species of cytochrome P-450 in liver mitochondria. The possible role of the liver mitochondrial cytochrome P-450 in the metabolism of vitamin D3 is discussed.
authors.affiliation: Department of Pharmaceutical Biochemistry, University of Uppsala, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Dahlbäck
authors.forename: K
authors.initials: K
authors.lastname: Wikvall
mesh_terms: D000818:Animals; D002458:Cell Fractionation; D002762:Cholecalciferol / Q000378:metabolism*; D002850:Chromatography, Gel; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005287:Ferredoxin-NADP Reductase / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism; D006900:Hydroxylation; D008930:Mitochondria, Liver / Q000201:enzymology*; D011817:Rabbits; D013053:Spectrophotometry; D013379:Substrate Specificity
chemical_list: D005288:Ferredoxins; D002762:Cholecalciferol; D003577:Cytochrome P-450 Enzyme System; D005287:Ferredoxin-NADP Reductase