title: 17 beta-estradiol hydroxylation catalyzed by human cytochrome P450 1B1.
abstract: The 4-hydroxy metabolite of 17 beta-estradiol (E2) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbon-receptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of E2. This activity was associated with human P450 1B1. To determine the relationship of the human P450 1B1 gene product and E2 4-hydroxylation, the protein was expressed in Saccharomyces cerevisiae. Microsomes from the transformed yeast catalyzed the 4- and 2-hydroxylation of E2 with Km values of 0.71 and 0.78 microM and turnover numbers of 1.39 and 0.27 nmol product min-1.nmol P450-1, respectively. Treatment of MCF-7 human breast cancer cells with the aryl hydrocarbon-receptor ligand indolo[3,2-b]carbazole resulted in a concentration-dependent increase in P450 1B1 and P450 1A1 mRNA levels, and caused increased rates of 2-, 4-, 6 alpha-, and 15 alpha-hydroxylation of E2. At an E2 concentration of 10 nM, the increased rates of 2- and 4-hydroxylation were approximately equal, emphasizing the significance of the low Km P450 1B1-component of E2 metabolism. These studies demonstrate that human P450 1B1 is a catalytically efficient E2 4-hydroxylase that is likely to participate in endocrine regulation and the toxicity of estrogens.
authors.affiliation: Department of Environmental Health Sciences, Johns Hopkins University, School of Hygiene and Public Health, Baltimore, MD 21205-2179, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Hayes
authors.forename: D C
authors.initials: DC
authors.lastname: Spink
authors.forename: B C
authors.initials: BC
authors.lastname: Spink
authors.forename: J Q
authors.initials: JQ
authors.lastname: Cao
authors.forename: N J
authors.initials: NJ
authors.lastname: Walker
authors.forename: T R
authors.initials: TR
authors.lastname: Sutter
mesh_terms: D000077584:2-Methoxyestradiol; D000595:Amino Acid Sequence; D001483:Base Sequence; D002227:Carbazoles / Q000494:pharmacology; D002384:Catalysis; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004247:DNA; D004958:Estradiol / Q000031:analogs & derivatives / Q000378:metabolism*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006900:Hydroxylation; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae
chemical_list: D002227:Carbazoles; D007211:Indoles; C075954:indolo(3,2-b)carbazole; C045018:4-methoxyestradiol; D004958:Estradiol; D000077584:2-Methoxyestradiol; D004247:DNA; D003577:Cytochrome P-450 Enzyme System