Dissociation of 19-hydroxy- 19-oxo-, and aromatizing-activities in human placental microsomes through the use of suicide substrates to aromatase.
Suicide substrates of aromatase were used as chemical probes to determine if free 19-hydroxyandrost-4-ene-3,17-dione (19-OHA) and 19-oxoandrost-4-ene-3,17-dione (19-oxoA) are obligatory intermediates in the aromatization of androst-4-ene-3,17-dione (androstenedione) to oestrone by human placental aromatase. A radiometric-HPLC assay was used to monitor 19-hydroxy, 19-oxo-, and aromatized products formed in incubations of [14C]androstenedione and human placental microsomes. When microsomes were preincubated with the suicide substrates 10 beta-mercapto-estr-4-ene-3,17-dione (10 beta-SHnorA), or 17 beta-hydroxy-10 beta-mercaptoestr-4-ene-3-one (10 beta-SHnorT), it was found that 19-hydroxy-, 19-oxo- and aromatase activities were inhibited in parallel. However, when the suicide substrates 4-hydroxyandrost-4-ene-3,17-dione (4-OHA) and 19-mercaptoandrost-4-ene-3,17-dione (19-SHA) were preincubated with placental microsomes, significantly greater inhibition of formation of oestrogens was observed in comparison to the inhibition of formation of 19-hydroxy- and 19-oxo-metabolites. Furthermore, significantly more time-dependent inhibition of 19-oxoA formation was observed in comparison to inhibition of 19-OHA formation with these same inhibitors. These results suggest that 19-hydroxy- and 19-oxo-androstenediones are not free, obligatory intermediates in the aromatization of androstenedione by human placental aromatase, but rather are products of their own autonomous cytochrome P-450-dependent, microsomal enzymatic activities.
Bednarski
P J
PJ
Department of Medicinal Chemistry, University of Washington, Seattle 98195.
Nelson
S D
SD
D000735:Androstenedione / Q000031:analogs & derivatives / Q000378:metabolism*; D001141:Aromatase / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004970:Estrone / Q000378:metabolism*; D005260:Female; D006801:Humans; D008861:Microsomes / Q000201:enzymology*; D010920:Placenta / Q000648:ultrastructure*
D004970:Estrone; D000735:Androstenedione; C014142:19-oxo-delta(4) androstene-3,17-dione; C011482:19-hydroxy-4-androstene-3,17-dione; D001141:Aromatase