title: Reversible, positive cooperative interaction of 11 beta-chloromethyl-[3H]estradiol-17 beta with the calf uterine estrogen receptor.
abstract: The binding of 11 beta-chloromethyl-[3H]estradiol-17 beta [3H]CME2) with the calf uterine estrogen receptor was investigated. The equilibrium binding analysis indicated a positive cooperative interaction yielding curvilinear Scatchard plots and Hill coefficients of 1.4-1.5. This positive cooperative interaction of [3H]CME2 was indistinguishable from the typical cooperative interaction of [3H]estradiol with the receptor. The apparent relative association constant and the relative binding affinity of CME2 for the estrogen receptor measured by competitive binding assay were 146 and 184%, respectively. The dissociation kinetics of [3H]CME2 from the receptor was biphasic, composed of a fast dissociating component (15%, t1/2 = 4 min at 0 degrees C; 9%, t1/2 = 4 min at 28 degrees C) and a slow dissociating component (85%, t1/2 greater than 50 h at 0 degrees C; 91%, t1/2 greater than 50 h at 28 degrees C). The dissociation kinetics of [3H]estradiol was also biphasic: the t1/2 of the fast dissociating component was 4 min at 0 and 28 degrees C and approximately 200 min for the slow dissociating component at both temperatures. The fraction of the slow [3H]estradiol dissociating component increased from 56 to 92% upon warming. Ethanol extraction and trichloroacetic acid treatment proved that the binding of [3H]CME2 is fully reversible. The unusual dissociation kinetics and the binding mechanism of CME2 are discussed.
authors.affiliation: Department of Pharmacology, Hebrew University School of Medicine, Jerusalem, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Sasson
authors.forename: J A
authors.initials: JA
authors.lastname: Katzenellenbogen
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D004958:Estradiol / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D011960:Receptors, Estrogen / Q000378:metabolism*; D014599:Uterus / Q000378:metabolism*
chemical_list: D011960:Receptors, Estrogen; D004958:Estradiol; C038957:11-beta-chloromethyl-estradiol