title: Mechanism of the third oxidative step in the conversion of androgens to estrogens by cytochrome P450 19A1 steroid aromatase.
abstract: Aromatase is the cytochrome P450 enzyme that cleaves the C10-C19 carbon-carbon bond of androgens to form estrogens, in a three-step process. Compound I (FeO(3+)) and ferric peroxide (FeO2(-)) have both been proposed in the literature as the active iron species in the third step, yielding an estrogen and formic acid. Incubation of purified aromatase with its 19-deutero-19-oxo androgen substrate was performed in the presence of (18)O2, and the products were derivatized using a novel diazo reagent. Analysis of the products by high-resolution mass spectrometry showed a lack of (18)O incorporation in the product formic acid, supporting only the Compound I pathway. Furthermore, a new androgen 19-carboxylic acid product was identified. The rates of nonenzymatic hydration of the 19-oxo androgen and dehydration of the 19,19-gem-diol were shown to be catalytically competent. Thus, the evidence supports Compound I and not ferric peroxide as the active iron species in the third step of the steroid aromatase reaction.
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine , Nashville, Tennessee 37232-0146, United States.
authors.forename: Francis K
authors.initials: FK
authors.lastname: Yoshimoto
authors.forename: F Peter
authors.initials: FP
authors.lastname: Guengerich
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D000728:Androgens / Q000378:metabolism*; D001141:Aromatase / Q000378:metabolism*; D004967:Estrogens / Q000378:metabolism*; D005561:Formates / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D000447:Aldehydes; D000728:Androgens; D004967:Estrogens; D005561:Formates; D014867:Water; C030544:formic acid; D001141:Aromatase; D010100:Oxygen