title: Interaction of the radiolabelled high-affinity anti-oestrogen [3H]H1285 with the cytoplasmic oestrogen receptor.
abstract: The high-affinity triarylethylene anti-oestrogen H1285 [4-(NN-diethylaminoethoxy)-beta-ethyl-alpha-(p-hydroxyphenyl) -4'-methoxystilbene] was tritiated to high specific radioactivity (35 Ci/mmol). Competition experiments between [3H]H1285 and H1285 or oestradiol demonstrated that both compounds would compete with [3H]H1285 for oestrogen-specific binding sites in rat uterine cytosol. [3H]H1285 had at least 10 times the affinity for the receptor compared with oestradiol at the 50% competition level. [3H]H1285 appeared to have at least twice the association rate for the oestrogen receptor compared with [3H]oestradiol. In addition, the dissociation half-life (t1/2) of specific binding of [3H]H1285 to oestrogen receptors at 0 degrees C was about 220 h compared with a value of 60 h for [3H]oestradiol. Because of the extremely slow dissociation of [3H]H1285 from the oestrogen receptor, we were able to compare the sedimentation profiles of [3H]H1285-receptor complexes with those of [3H]oestradiol-receptor complexes in the presence of 0.4 M-KCl on 5-20% sucrose density gradients. [3H]Oestradiol-receptor complexes had a major peak at 4.4 S with a smaller peak at 5.6 S, whereas with [3H]H1285-receptor complexes the 5.6 S peak was always higher than the 4.4 S peak. There was significant variation between the dissociation behaviour at 20 degrees C of [3H]H1285-receptor complexes and [3H]oestradiol-receptor complexes pre-activated at 25 degrees C for 30 min in the presence and in the absence of 10 mM-sodium molybdate. The dissociation t1/2 of [3H]oestradiol-receptor complexes at 20 degrees C decreased from 1.5 h to 0.5 h when molybdate was present during heat treatment whereas the dissociation t1/2 for [3H]H1285-receptor complexes was 5 h for both conditions. These observations indicate that there are fundamental differences in the initial interaction of H1285 and oestradiol with the oestrogen receptor.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002499:Centrifugation, Density Gradient; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D003593:Cytoplasm / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D004965:Estrogen Antagonists / Q000378:metabolism*; D005260:Female; D046911:Macromolecular Substances; D051381:Rats; D011919:Rats, Inbred Strains; D011960:Receptors, Estrogen / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D004965:Estrogen Antagonists; D046911:Macromolecular Substances; D011960:Receptors, Estrogen; D013629:Tamoxifen; D004958:Estradiol; C039305:H 1285