title: Overview of regulatory cytochrome P450 enzymes of the vitamin D pathway.
abstract: Cytochromes P450c1 and P450c24 are regulated hydroxylase enzymes that direct the bioactivation and metabolic degradation of vitamin D. The bioactivation pathway is regulated by cytochrome P450c1 through its synthesis of 1alpha,25(OH)(2)D(3), the hormonally active form of the vitamin. Expression of the P450c1 gene is regulated at the transcription level. Promoter regions within the P450c1 gene have been identified that respond to cAMP and 1alpha,25(OH)(2)D(3) during the respective up- and down-regulation of P450c1 gene expression. The diametric action of 1alpha,25(OH)(2)D(3) to up-regulate P450c24 gene expression is discussed in the context of two vitamin D response elements (VDREs) that are linked functionally to an adjoining Ets-binding site. It is apparent from sequence-derived data that the P450c1 and P450c24 enzymes share only 10-25% sequence identity, yet they display functionally similar domains that are conserved across the family of cytochrome P450 enzymes. Expression of E. coli recombinant P450c1 and P450c24 enzymes, and the substrate-binding parameters for P450c24 are discussed. Finally, the natural point mutations in human P540c1 from patients with pseudovitamin D-deficiency rickets (PDDR) are discussed in the context of the enzyme's structure and function.
authors.affiliation: University of New Mexico School of Medicine, Department of Biochemistry and Molecular Biology, Albuquerque, New Mexico 87131-5221, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Omdahl
authors.forename: E A
authors.initials: EA
authors.lastname: Bobrovnikova
authors.forename: S
authors.initials: S
authors.lastname: Choe
authors.forename: P P
authors.initials: PP
authors.lastname: Dwivedi
authors.forename: B K
authors.initials: BK
authors.lastname: May
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002117:Calcitriol / Q000096:biosynthesis; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D014807:Vitamin D / Q000378:metabolism* / Q000502:physiology
chemical_list: D014807:Vitamin D; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D002117:Calcitriol