A novel class of inactive steroid-binding sites in female rat liver nuclei

Abstract

Nuclear salt extracts from intact female rat liver showed insignificant levels of progesterone-, oestradiol-, testosterone- or dexamethasone-specific binding. However, brief exposure of nuclear extracts to dextran-coated charcoal (DCC) induced binding for all the above classes of steroids. This 'DCC-effect', which was reproduced neither by gel filtration nor by extensive dialysis of the nuclear extract, could not be ascribed to removal of endogenous free or loosely bound steroids. We show that rat liver nuclei contain a class of secondary binding sites (BSII), which exhibit moderate or low affinity for steroid ligands, positive co-operativity, and cross-reaction between classes of steroids. The capacity of BSII sites to bind steroids depends strictly on prior neutralization by DCC of endogenous heat-stable non-dialysable inhibitor(s). The putative roles of these BSII binding sites are discussed in relation to component(s) probably responsible for inhibitory activity.

Progesterone receptor in the mammary tissue of pregnant and lactating gilts and the effect of tamoxifen treatment during late gestation

“…Aliquots of steroids (0-2 nmol-2 µ ) were pipetted into glass tubes (10 75 mm) and dried under a stream of nitrogen. Aliquots (250 µ ) of the cytosol in duplicate were incu¬ bated with [3H]progesterone (0-2-10 nmol/tube) in the presence or absence of a 100-fold molar excess of unlabelled progesterone and a 50-fold molar excess of cortisol in each tube, for 16-20 h. After incubation, the quantity of bound [3H]progesterone in each was determined by gel filtration using minicolumns (0-45 cm 7 cm) of Sephadex LH-20, adapted from the method of Ginsburg, Greenstein, MacLusky et al (1974) and Bechet & Perry (1987). The incubation mixture (250 pi) was applied to a minicolumn of Sephadex LH-20 and eluted with 0-8 ml assay buffer, the entire peak of macromolecular-bound [3H]progesterone was collected in scintillation vials and the radioactivity counted using a Packard 1500 Tricarb liquid scintillation analyser.…”