Abstract:
The mechanistic aspects of the 19-hydroxy1ation and aromatization
of androgens were investigated. Fungal, bacterial and mammalian
enzymatic activities were studied in this regard .
The fungus Pell i cular~ fi1amentosa metabolized androst-4-ene-3 ,
17-dione to the corresponding 110<' , 11 f and 14 0( hydroxylated derivatives.
No ~19- hydroxylated products were isolated, although this
transformation was previously observed for the C21-steroids .
The intestinal bacterium Clostridi um paraputrific~ had been reported
to aromatize androsten-4-ene-3,17-dione. In the present study,
however, only the ring A reduced products , 17(3 - hydroxy-5f -andro8tane-
3-one and 5f-androstane-3,17-dione , were recovered .
Human placental microsomes contain substantial aromatase activity
and were employed in an effort to elucidate some of the mechanistic
details of aromatization.
Selectively deuterated steroidal substrates were employed as a
probe in order to distinguish b'!tween certain of the mechanisms proposed
for aromatization . Retention of deuterium at C4 and C6 was observed.
It was concluded that no free intermediates allowing for loss of hydrogen
from either of these two positions are implicated in this process .
The involvement of a Schiff base enzyme-sup strate complex in aromatization
was examined using the substrate 17f - hydroxyandrost-4-ene-3-one-
3_ 1BO. Since no loss of label was ob~erved, the implication of a Schiff
base was discounted .
Mixed label1ir~ studies were performed in order to determine if
hydroxylation at C19 is a rate-determining process in aromatization .
Isotope effects of 2 .1 and 1.7 were determined for the conversion of
17f - hydroxyandrost-4-ene-J-one-19,19,19-dJ and -19-dl respectively
to estrogens. It was concluded from this that 19-hydroxylation is
at l east a partially rate-determinjng process in aromatization.
A homoenb~ation mechanism for 19-hydroxylation was not supported
by the data obtained in this s tudy.
In vitro 1JC NMR monitoring using l7f-hydroxyandrost-4-ene-Jone-
19-l3C was found not to be a successful approach in the study of
steroid transformations, owing in part t o their low solubility in the
incubation medium.
