The interaction of rat uterine cytosol oestrogen-receptor complexes with the synthetic acceptor oligo(dT)-cellulose was studied. Differences in the stability of receptor complexes and their ability to bind to oligo(dT)-cellulose on storage at 4 degrees C or when exposed to increased temperatures indicated heterogeneity of steroid- and oligonucleotide-binding sites. Dilution, dialysis and (NH4)2SO4 precipitation increased the interaction of receptor complexes with oligo(dT)-cellulose (a step termed activation). This increase may be the result of the removal of low-molecular-weight cytosol components which inhibit receptor activation, dimerization to the 5 S form, which binds to oligo(dT)-cellulose, or interaction of 5 S receptor with the oligonucleotide. Cytosol oestradiol-receptor complexes exhibited biphasic dissociation kinetics. All these manipulations resulted in an increase in the proportion of the slow-dissociating component equivalent to the increase in receptor binding to oligo(dT)-cellulose. In contrast, addition of 10mM-sodium molybdate to cytosol decreased both oligo(dT)-cellulose binding and the proportion of receptor with slow dissociation kinetics. The inclusion of proteinase inhibitors did not affect interactions of receptor with oligo(dT)-cellulose nor the dissociation kinetics. These results suggest that oligo(dT)-cellulose binding may serve to quantify the proportion of cytosol receptor in an active form capable of nuclear interaction and to help to ascertain whether a receptor system is fully functional. This binding procedure could prove useful in the evaluation of oestrogen responsivity under normal and pathological conditions.

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