title: Different mechanisms of hydroxylation site selection by liver and kidney cytochrome P450 species (CYP27 and CYP24) involved in vitamin D metabolism.
abstract: A series of homologated 1 alpha-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 molecules with one to three extra carbons in the side chain were used to examine the substrate preferences and hydroxylation site selection mechanisms of the liver vitamin D3-25-hydroxylase (CYP27) and the target cell 25-hydroxyvitamin D3-24-hydroxylase (CYP24). Cultured and transfected cell models, used as sources of these hydroxylases, gave 23-, 24-, 25-, and 27-hydroxylated metabolites which were identified by their high performance liquid chromatography and GC-MS characteristics. Lengthening the side chain is tolerated by each cytochrome P450 isoform such that 25-hydroxylation or 24-hydroxylation continues to occur at the same rate as in the native side chain, while the site of hydroxylation remains the same for the liver enzyme in that CYP27 continues to hydroxylate at C-25 and C-27 (minor) despite the two-carbon-atom extension. Somewhat surprising is the finding that C-24 and C-23 (minor) hydroxylations also do not change as the side chain is extended by as much as three carbons. We conclude that CYP24 must be directed to its hydroxylation site(s) by the distance of carbon 24 from the vitamin D ring structure and not as in CYP27 by the distance of the hydroxylation site from the end of the side chain.
authors.affiliation: Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
authors.forename: F J
authors.initials: FJ
authors.lastname: Dilworth
authors.forename: I
authors.initials: I
authors.lastname: Scott
authors.forename: A
authors.initials: A
authors.lastname: Green
authors.forename: S
authors.initials: S
authors.lastname: Strugnell
authors.forename: Y D
authors.initials: YD
authors.lastname: Guo
authors.forename: E A
authors.initials: EA
authors.lastname: Roberts
authors.forename: R
authors.initials: R
authors.lastname: Kremer
authors.forename: M J
authors.initials: MJ
authors.lastname: Calverley
authors.forename: H L
authors.initials: HL
authors.lastname: Makin
authors.forename: G
authors.initials: G
authors.lastname: Jones
mesh_terms: D002117:Calcitriol / Q000378:metabolism; D002460:Cell Line; D053493:Cholestanetriol 26-Monooxygenase; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D006801:Humans; D006900:Hydroxylation; D007668:Kidney / Q000201:enzymology*; D008099:Liver / Q000201:enzymology*; D013250:Steroid Hydroxylases / Q000502:physiology*; D014807:Vitamin D / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D014807:Vitamin D; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol