ABSTRACT
The observed rate of dissociation of radioactive estradiol from nuclear estrogen-receptor complexes from hen oviduct has been shown to depend to a large extent on the method used to initiate dissociation. The present study indicates that nuclear progesterone receptors display the same pattern of behavior. Dissociation kinetics of nuclear progesterone receptor extracted from hen oviducts were affected by the method of initiation of dissociation; the rate of dissociation at 25 degrees C when dissociation was initiated with unlabeled steroid was three times that observed when dissociation was initiated by addition of a charcoal/dextran suspension. In contrast to nuclear receptors, both estrogen and progesterone receptors prepared from cytosol displayed only a single rate of dissociation, no matter what the method of initiation of dissociation. These results strengthen the idea that nuclear receptors contain a factor or subunit which may be removed by charcoal, which alters the rate of dissociation of steroid from the complex.
