J. Biol. Chem., Vol. 255, Issue 9, 4068-4072, May, 1980
Effects of pyridoxal 5'-phosphate on uterine estrogen receptor. II. Inhibition of estrogen . receptor transformation
A Traish, RE Muller and HH Wotiz
Previous observations suggested that pyridoxal 5'-phosphate was capable of
inhibiting estrogen . receptor (R . E2) activation, or translocation to the
nucleus, or both. The present study attempts to define more specifically
the locus of this action. To this end we have examined the physicochemical
alteration produced by interaction of pyridoxal 5'- phosphate with estrogen
. receptor complex, using sucrose density gradient analysis and
dissociation kinetics. Receptor transformation was inhibited when
activation was performed in the presence of pyridoxal 5'-phosphate. This
effect was protein- and pyridoxal 5'- phosphate concentration-dependent.
When pyridoxal 5'-phosphate was introduced postactivation it did not have
any effect on the activated receptor, but when similar treatment was
followed by NABH4 reduction, the complex reverted to the monomeric entity.
The dissociation behavior obtained with cytosol R . E2, warmed in the
presence of pyridoxal 5'- phosphate, showed a biphasic curve suggesting
that a significant portion of receptors remained nonactivated as
demonstrated by the fast dissociating component. Due to the fact that Tris
buffers cannot be used for pyridoxal 5'-phosphate experiments, we have used
a borate buffer which resulted in a displacement of the sedimentation
values from a 4S to 4.6 S for the unactivated receptor and 5S to 6 S for
the activated form. The observations reported suggest that at least the
initial effect of pyridoxal 5'-phosphate results in the inhibition of
cytosolic receptor transformation from the nonactivated to the activated
form.
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