title: Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogens: A site-directed mutagenesis study.
abstract: Flavone and isoflavone phytoestrogens are plant chemicals and are known to be competitive inhibitors of cytochrome P450 aromatase with respect to the androgen substrate. Aromatase is the enzyme that converts androgen to estrogen; therefore, these plant chemicals are thought to be capable of modifying the estrogen level in women. In this study, the inhibition profiles of four flavones [chrysin (5, 7-dihydroxyflavone), 7,8-dihydroxyflavone, baicalein (5,6,7-trihydroxyflavone), and galangin (3,5,7-trihydroxyflavone)], two isoflavones [genistein (4,5,7-trihydroxyisoflavone) and biochanin A (5,7-dihydroxy-4-methoxyisoflavone)], one flavanone [naringenin (4, 5,7-trihydroxyflavanone)], and one naphthoflavone (alpha-naphthoflavone) on the wild-type and six human aromatase mutants (I133Y, P308F, D309A, T310S, I395F, and I474Y) were determined. In combination with computer modeling, the binding characteristics and the structure requirement for flavone and isoflavone phytoestrogens to inhibit human aromatase were obtained. These compounds were found to bind to the active site of aromatase in an orientation in which rings A and C mimic rings D and C of the androgen substrate, respectively. This study also provides a molecular basis as to why isoflavones are significantly poorer inhibitors of aromatase than flavones.
authors.affiliation: Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
authors.forename: Y C
authors.initials: YC
authors.lastname: Kao
authors.forename: C
authors.initials: C
authors.lastname: Zhou
authors.forename: M
authors.initials: M
authors.lastname: Sherman
authors.forename: C A
authors.initials: CA
authors.lastname: Laughton
authors.forename: S
authors.initials: S
authors.lastname: Chen
mesh_terms: D000818:Animals; D001141:Aromatase / Q000235:genetics; D047072:Aromatase Inhibitors; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004968:Estrogens, Non-Steroidal / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D007529:Isoflavones / Q000494:pharmacology*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000187:drug effects*; D048789:Phytoestrogens; D028321:Plant Preparations; D010944:Plants / Q000737:chemistry*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors; D004968:Estrogens, Non-Steroidal; D005419:Flavonoids; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations; D001141:Aromatase