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J. Biol. Chem., Vol. 266, Issue 12, 7410-7416, 04, 1991
SL Pahuja, JE Zielinski, G Giordano, WJ McMurray and RB Hochberg
Biological esterification with fatty acids is a feature that is now known
to be common to most steroids. The esterification of estradiol in the
D-ring at the 17 beta-hydroxyl leads to a family of extremely active
estrogens. Similarly, esterification of the weaker estrogen, estriol (E3),
has an even greater impact on its hormonal potency. We have recently shown
that synthetic long chain esters of E3 at either 16 alpha- or 17 beta- are
highly potent estrogens. The estrogenic activity of the synthetic E3 esters
led us to determine whether E3 is biologically esterified, and if so, to
characterize the resulting esters. Incubation of E3 with rat lung, a tissue
which is highly active in esterifying estradiol, produces a nonpolar
metabolite which upon saponification is converted back into E3. There was
no evidence for the formation of a diester. Purification by high
performance liquid chromatography separates the non-polar metabolite into
two peaks, one the C-16 alpha- (approximately 60%) and the other the C-17
beta-ester (approximately 40%). The two fractions were further purified and
characterized; each is a mixture of fatty acid esters of E3. The
composition of the C-16 alpha- and the C-17 beta-fatty acid esters of E3 is
identical. The predominant fatty acids are arachidonate, 34%, palmitate,
26%, followed by oleate 14%, linoleate 13%, stearate 8%, and palmitoleate
5%. The similarity of the esters at C-16 and C-17 may indicate that the
fatty acid precursor for the acyltransferase is the same for both hydroxyl
groups. It may also suggest that the same enzyme esterifies both positions
in the D-ring. Since synthetic estriol fatty acid esters are extremely
potent and long-lived estrogens, the enzymatic esterification of estriol
produces powerful estrogens with considerable physiological potential.
The biosynthesis of D-ring fatty acid esters of estriol
Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, Connecticut 06510.
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