In vitro inactivation of the oestradiol receptor by a lysosome-enriched fraction from rat uterus.

Abstract

The inactivating action of a lysosome-enriched fraction on oestradiol receptors from rat uterus cytosol under in vitro conditions is reported. During incubation at 25 degrees C in the absence of oestradiol, the inactivation of the oestradiol receptor depends directly on the amount of lysosome-enriched fraction present. Boiled lysosome-enriched fractions have no effect on cytosol receptors. The inactivation of oestradiol receptors was maximal when the incubation was performed at pH 7.5 and follows second order kinetics. Progesterone receptors were also lost during the incubation but two other proteins present in cytosol (aldolase and lactate dehydrogenase) show almost no change in amount during the procedure. It appears that the inactivating process reflects the action of quite specific entities present in the lysosome-enriched fraction. The effect of the lysosome-enriched fraction on cytosol oestradiol receptors is quantitative as judged from unchanged KA value and electrophoretic mobility of the surviving receptors.