title: Catalytic differences between porcine blastocyst and placental aromatase isozymes.
abstract: Two isozymes of porcine aromatase, the placental and the blastocyst forms, were expressed in CHO cells using the mammalian cell transfection method. Using an 'in-cell' assay (a 3H-water release method), catalytic parameters of the porcine placental aromatase were found to be very similar to those of the human enzyme; however, the activity of the blastocyst isozyme was found to be one-thirtieth that of the placental isozyme. Product isolation assay (using testosterone as the substrate) revealed that the major steroid products were 17beta-estradiol and 19-nortestosterone. The product ratio of estradiol/19-nortestosterone was found to be 94 : 6 for the porcine placental form, 6 : 94 for the porcine blastocyst form, and 92 : 8 for the human wild-type aromatase. Therefore, the porcine blastocyst aromatase isozyme catalyzes mainly androgen 19-desmethylation rather than aromatization. In addition, inhibition profile analyses on the placental and blastocyst isozymes were performed using three steroidal inhibitors [4-hydroxyandro-stenedione (4-OHA), 7alpha-(4'-amino)phenylthio-1, 4-androstandiene-3,17-dione (7alpha-APTADD), and bridge (2, 19-methyleneoxy) androstene-3,17-dione (MDL 101,003)], and four nonsteroidal inhibitors [aminoglutethimide (AG), CGS 20267, ICI D1033, and vorozole (R83842)]. While the two isozymes of porcine aromatase share 93% amino-acid sequence identity, our results indicate that the two porcine aromatase isozymes have distinct responses to various aromatase inhibitors.
authors.affiliation: Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA, USA.
authors.forename: Y C
authors.initials: YC
authors.lastname: Kao
authors.forename: T
authors.initials: T
authors.lastname: Higashiyama
authors.forename: X
authors.initials: X
authors.lastname: Sun
authors.forename: T
authors.initials: T
authors.lastname: Okubo
authors.forename: C
authors.initials: C
authors.lastname: Yarborough
authors.forename: I
authors.initials: I
authors.lastname: Choi
authors.forename: Y
authors.initials: Y
authors.lastname: Osawa
authors.forename: F A
authors.initials: FA
authors.lastname: Simmen
authors.forename: S
authors.initials: S
authors.lastname: Chen
mesh_terms: D000818:Animals; D001141:Aromatase / Q000378:metabolism*; D001755:Blastocyst / Q000201:enzymology*; D016466:CHO Cells; D002384:Catalysis; D006224:Cricetinae; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011994:Recombinant Proteins / Q000378:metabolism; D013552:Swine; D014162:Transfection
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D001141:Aromatase