title: Purification and characterization of a vitamin D3 25-hydroxylase from pig liver microsomes.
abstract: A cytochrome P-450 which catalyses 25-hydroxylation of vitamin D3 has been purified to apparent homogeneity from pig liver microsomes. The specific content of cytochrome P-450 was 12 nmol.mg of protein-1, and the preparation showed a single band with an apparent M(r) of 50,500 upon SDS/PAGE. A monoclonal antibody raised against the vitamin D3 25-hydroxylase reacted strongly with the purified 25-hydroxylating cytochrome P-450 from pig kidney microsomes [Bergman & Postlind (1990) Biochem. J. 270, 345-350]. The liver enzyme showed structural and functional properties very similar to those of the kidney enzyme. The two enzymes differed with respect to only one of the first 16 N-terminal amino acids. The vitamin D3 25-hydroxylase in pig liver microsomes exhibited a turnover and an apparent Km for 25-hydroxylation of vitamin D3 which were of the same order of magnitude as those of a well-characterized male-specific 25-hydroxylating cytochrome P-450 in rat liver microsomes. The two enzymes differed structurally. The pig liver enzyme was, in contrast to the rat liver enzyme, not sex-specific, and did not catalyse 16 alpha-hydroxylation of testosterone. These properties of the 25-hydroxylase in rat liver microsomes have led to questions on the role of microsomal 25-hydroxylation of vitamin D3. It is concluded that studies on microsomal 25-hydroxylation with the rat may be misleading. The results of the present study show that the pig appears to be a representative species for evaluation of vitamin D3 hydroxylases in other mammals, including man.
authors.affiliation: Department of Pharmaceutical Biochemistry, University of Uppsala, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Axén
authors.forename: T
authors.initials: T
authors.lastname: Bergman
authors.forename: K
authors.initials: K
authors.lastname: Wikvall
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D053493:Cholestanetriol 26-Monooxygenase; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D000072467:Cytochrome P450 Family 2; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D006900:Hydroxylation; D007525:Isoelectric Focusing; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D013057:Spectrum Analysis; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D013552:Swine
chemical_list: D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase