title: An antiestrogen-binding protein in human tissues.
abstract: Although nonsteroidal antiestrogens of the triphenylethylene type are generally considered to act through the estrogen receptor, some observations suggest that estrogen target tissues may also contain a binding protein specific for these compounds. The data so far reported, however, are also consistent with ligand-induced changes in conformation or in the state of aggregation of the estrogen receptor. The studies reported here demonstrate the existence of a protein in human myometrial cytosol which binds 1-[4-(2-dimethylaminoethoxy)phenyl]1,2-diphenylbut-1(Z)-ene ([3H]tamoxifen) with high affinity (Kd = 2.3 X 10(-9) M). This protein exhibits striking specificity for nonsteroidal antiestrogens. Estradiol competes weakly for bound [3H]tamoxifen, while other estrogens and nonestrogenic steroid hormones do not compete at all. Sedimentation analysis and molecular sieve chromatography indicate that the antiestrogen-binding protein is a larger species than the estrogen receptor and elutes from DEAE-Sephacel at a lower KCl concentration (0.03 M) than the estrogen receptor (0.15 M). Differential thermal stability of the estrogen receptor and the antiestrogen-binding protein was demonstrable in the absence of added ligand. The antiestrogen-binding protein was ubiquitous, being present in many tissues where estrogen receptor was undetectable. These findings support the separate existence of an antiestrogen-binding protein.
mesh_terms: D001667:Binding, Competitive; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D009215:Myometrium / Q000378:metabolism*; D011247:Pregnancy; D011955:Receptors, Drug; D011960:Receptors, Estrogen / Q000302:isolation & purification / Q000378:metabolism*; D013629:Tamoxifen / Q000378:metabolism; D014018:Tissue Distribution; D014599:Uterus / Q000378:metabolism*
chemical_list: D011955:Receptors, Drug; D011960:Receptors, Estrogen; D013629:Tamoxifen