Abstract
ABSTRACT The reductive metabolism of 16-oxo-oestrone (3-hydroxy-Δ 1,3,5(10)-oestratriene-16,17-dione) has been studied in the 10 000 × g supernatant fraction, in the cytoplasmic fraction (100 000 × g supernatant) and in the microsomal fraction of human placenta. All metabolites formed from 16-oxo-oestrone were identified by paperchromatography and by various microchemical reactions. After incubation of 16-oxo-oestrone with the 10 000 × g supernatant in the presence of ATP, NAD+ and nicotinamide, 16-oxo-17β-oestradiol, oestriol and 16-epi-oestriol were detected as metabolites. When 16-oxooestrone was incubated with the cytoplasmic fraction and NADH or the NADPH-generating system, the following compounds were formed: 16α-hydroxyoestrone, 16β-hydroxyoestrone, 16-oxo-oestradiol-17β, oestriol and 16-epi-oestriol. The time course of the incubation revealed that 16α- and 16β-hydroxyoestrone were reduced rapidly to oestriol and 16-epi-oestriol, respectively; after 30 min of incubation, the two 16,17-ketols had completely disappeared. Incubation of 16-oxo-oestrone with the microsomal fraction in the presence of NADH or the NADPH-generating system yielded 16-oxo-17β-oestradiol, oestriol and 16-epi-oestriol. The results obtained demonstrate that the cytoplasmic fraction contains – in addition to the already known 17β-hydroxysteroid oxidoreductase – a 16β- as well as a 16α-hydroxysteroid oxidoreductase. The highest activity is shown by the 17β-enzyme, followed by the 16β- and 16α-enzyme. In the microsomal fraction, there are also present a 17β- and a 16β-hydroxysteroid oxidoreductase; however, no 16α-hydroxysteroid oxidoreductase could be detected. On the basis of kinetic experiments, it is concluded that pronounced differences exist in enzyme activity and substrate specificity between the cytoplasmic and the microsomal 17β-hydroxysteroid oxidoreductase of human placenta.
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