Different catalytic properties and inhibitor responses of the goldfish brain and ovary aromatase isozymes

The brain and ovarian aromatase isozymes of goldfish (Carassius auratus) ar e encoded by different CYP19 genes. This study measured aromatase activity in the goldfish brain tissues. For a direct comparison of the properties of the two aromatase isozymes, Chinese hamster ovary cells were stably transf ected with brain- and ovary-derived cDNAs (respectively, P450aromB and -A) and the properties of the expressed isozymes were compared. The kinetic par ameters of the two isozymes were determined using androstenedione and testo sterone as substrates and compared to those of human aromatase. Inhibition profile analyses on the two isozymes were performed using seven inhibitors [4-hydroxyandrostene-dione, 7 alpha-(4'-amino)phenylthio-1,4-androstadiene- 3,17-dione, bridge (2,19-methyleneoxy)androstene-3,17-dione, aminoglutethim ide (AG), CGS 20267, ICI D1033, and vorozole]. Except for AG, the compounds tested were found to be much stronger inhibitors against the ovary enzyme than the brain enzyme. In addition, the ovary isoform was more sensitive to two phytoestrogens, chrysin and 7,8-dihydroxyflavone, than the brain form. These studies reveal that catalytic properties of the goldfish aromatase i soforms are significantly different from those of human aromatase. In addit ion, differences in the K-i values of aromatase inhibitors for the two gold fish isoforms suggest structural variance in the active sites of these isoz ymes. (C) 2001 Academic Press.