Metabolism of 19-methyl-substituted steroids by human placental aromatase.
The 19-methyl analogues of androstenedione and its aromatization intermediates (19-hydroxyandrostenedione and 19-oxoandrostenedione) were evaluated as substrates of microsomal aromatase in order to determine the effect of a 19-alkyl substituent on the enzyme's regiospecificity. Neither the androstenedione analogue [10-ethylestr-4-ene-3,17-dione (1c)] nor the 19-oxoandrostenedione analogue [10-acetylestr-4-ene-3,17-dione (3c)] was converted to estrogens or oxygenated metabolites by placental microsomes. In contrast, both analogues of 19-hydroxyandrostenedione [10-[(1S)-1-hydroxyethyl]estr-4-ene-3,17-dione (2c) and 10-[(1R)-1-hydroxyethyl]estr-4-ene-3,17-dione (2e)] were converted to the intermediate analogue 3c in a process requiring O2 and either NADH or NADPH. No change in enzyme regiospecificity was detected. The absolute configuration of 2e was determined by X-ray crystallography. Experiments with 18O2 established that 3c generated from 2c retained little 18O (less than 3%), while 3c arising from 2e retained a significant amount of 18O (approximately equal to 70%). All four 19-methyl steroids elicited type I difference spectra from placental microsomes in addition to acting as competitive inhibitors of aromatase (KI = 81 nM, 11 microM, 9.9 microM, and 150 nM for 1c, 2c, 2e, and 3c, respectively). Pretreatment of microsomes with 4-hydroxyandrostenedione (a suicide inactivator of aromatase) abolished the metabolism of 2c and 2e to 3c, as well as the type I difference spectrum elicited by 2c and 2e.(ABSTRACT TRUNCATED AT 250 WORDS)
Beusen
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DD
Department of Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110.
Carrell
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HL
Covey
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D001141:Aromatase / Q000378:metabolism*; D005260:Female; D006801:Humans; D007202:Indicators and Reagents; D008745:Methylation; D008861:Microsomes / Q000201:enzymology*; D008958:Models, Molecular; D008968:Molecular Conformation; D010920:Placenta / Q000201:enzymology*; D013379:Substrate Specificity; D045165:Testosterone Congeners / Q000138:chemical synthesis / Q000378:metabolism*
D007202:Indicators and Reagents; D045165:Testosterone Congeners; D001141:Aromatase