Comparison of cytochrome P-450 species which catalyze the hydroxylations of the aromatic ring of estradiol and estradiol 17-sulfate.
For identification of microsomal cytochrome P-450 (P-450) enzymes which catalyze 2- or 4-hydroxylations of estrogens in the rat liver, estradiol (E2) and estradiol 17-sulfate (E2-17-S) were selected as the substrates and incubated with various kinds of purified P-450 enzymes: PB-1, PB-2, PB-4 and PB-5 obtained from phenobarbital-treated male rats (Sprague-Dawley); MC-1 and MC-5 from 3-methylcholanthrene-treated male rats; and UT-1, UT-2, UT-4 and UT-5 from untreated animals. The reactions were carried out under the P-450-reconstructed system, and the resulting products were determined by HPLC using electrochemical detection. All the enzymes tested were shown to have varying degrees of catalytic activities for 2-hydroxylation of the two substrates; UT-1 and UT-2 had the highest activity. Of the induced P-450 enzymes, PB-2 and MC-1 showed fairly high catalytic activity for 4-hydroxylation of E2. The P-450 enzymes obtained from the untreated male rats, especially UT-4, showed the highest catalytic activity for 4-hydroxylation of the two substrates. From these results and also from kinetic experiments, the P-450 enzymes which catalyze 2- and 4-hydroxylations of estrogen were considered to be different species. A part of E2 was converted to such metabolites as estrone and those having a hydroxyl group at positions 6 beta, 15 alpha or 16 alpha, each production of which was estimated to be catalyzed by single or multiple P-450s.
Watanabe
K
K
Hokkaido Institute of Pharmaceutical Sciences, Japan.
Takanashi
K
K
Imaoka
S
S
Funae
Y
Y
Kawano
S
S
Inoue
K
K
Kamataki
T
T
Takagi
H
H
Yoshizawa
I
I
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000378:metabolism*; D002393:Estrogens, Catechol; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D002393:Estrogens, Catechol; C048615:estradiol 17-sulfate; D004958:Estradiol; D008748:Methylcholanthrene; C060524:2-hydroxyestradiol 17-sulfate; D003577:Cytochrome P-450 Enzyme System; C069759:4-hydroxyestradiol 17-sulfate; C001390:2-hydroxyestradiol; C014036:4-hydroxyestradiol; D010634:Phenobarbital