title: Kinetic analysis of reversible inhibition of 16alpha-hydroxyandrostenedione aromatization in human placental microsomes by suicide substrates of androstenedione aromatization.
abstract: To gain insight into the catalytic function of aromatase and its substrate specificity, we studied reversible inhibition of 16alpha-hydroxyandrostenedione (16alpha-OHAD) aromatization in human placental microsomes by several suicide substrates of androstenedione (AD) aromatization, including 4-hydroxyAD (1), 6-oxoAD (2) and its 19-hydroxy analogue 3, androst-5-ene-4,7,17-trione (4), and 10beta-acetoxyandrost-5-en-7,17-dione (5) that, in contrast, do not cause a suicide inactivation of 16alpha-OHAD aromatization. All inhibitors examined blocked 16alpha-OHAD aromatization in a competitive manner with apparent K(i) values ranging from 0.50 to 980 nM. The relative K(i) values between inhibitors 1-5 obtained in the 16alpha-OHAD aromatization experiments were markedly different from those obtained in the AD aromatization experiments. The results predict that all inhibitors examined bind to the 16alpha-OHAD binding site in a manner that does not cause suicide inactivation of 16alpha-OHAD aromatization. These findings would be useful for understanding the active (binding) site structure as well as the catalytic function of aromatase.
authors.affiliation: Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai 981-8558, Japan. numazawa@tohoku-pharm.ac.jp
authors.forename: Mitsuteru
authors.initials: M
authors.lastname: Numazawa
authors.forename: Ayako
authors.initials: A
authors.lastname: Mutsumi
authors.forename: Mii
authors.initials: M
authors.lastname: Tachibana
authors.forename: Akiko
authors.initials: A
authors.lastname: Yoshimura
mesh_terms: D000735:Androstenedione / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology*; D001141:Aromatase / Q000378:metabolism; D047072:Aromatase Inhibitors; D001665:Binding Sites; D001667:Binding, Competitive; D002384:Catalysis; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D010920:Placenta / Q000201:enzymology; D013379:Substrate Specificity
chemical_list: D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors; D000735:Androstenedione; C018202:16-hydroxyandrost-4-en-3,17-dione; D001141:Aromatase