title: Metabolism of A-ring diastereomers of 1alpha,25-dihydroxyvitamin D3 by CYP24A1.
abstract: The metabolism of 1alpha,25(OH)(2)D(3) (1alpha,3beta) and its A-ring diastereomers, 1beta,25(OH)(2)D(3) (1beta,3beta), 1alpha,25(OH)(2)-3-epi-D(3) (1alpha,3alpha), and 1beta,25(OH)(2)-3-epi-D(3) (1beta,3alpha), was examined to compare the substrate specificity and reaction specificity of CYP24A1 between humans and rats. The ratio between C-23 and C-24 oxidation pathways in human CYP24A1-dependent metabolism of (1alpha,3alpha) and (1beta,3alpha) was 1:1, although the ratio for (1alpha,3beta) and (1beta,3beta) was 1:4. These results indicate that the orientation of the hydroxyl group at the C-3 position determines the ratio between C-23 and C-24 oxidation pathways. A remarkable increase of metabolites in the C-23 oxidation pathway was also observed in rat CYP24A1-dependent metabolism. The binding affinity of human CYP24A1 for A-ring diastereomers was (1alpha,3beta)>(1alpha,3alpha)>(1beta,3beta)>(1beta,3alpha), indicating that both hydroxyl groups at C-1 and C-3 positions significantly affect substrate-binding. The information obtained in this study is quite useful for understanding substrate recognition of CYP24A1 and designing new vitamin D analogs.
authors.affiliation: Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Kusudo
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sakaki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Abe
authors.forename: Toshie
authors.initials: T
authors.lastname: Fujishima
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kittaka
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Takayama
authors.forename: Susumi
authors.initials: S
authors.lastname: Hatakeyama
authors.forename: Miho
authors.initials: M
authors.lastname: Ohta
authors.forename: Kuniyo
authors.initials: K
authors.lastname: Inouye
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000737:chemistry* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D066298:In Vitro Techniques; D007536:Isomerism; D007700:Kinetics; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013045:Species Specificity; D013237:Stereoisomerism; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013379:Substrate Specificity; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; C585551:Cyp24a1 protein, rat; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol