title: Positive cooperativity of the estrogen receptor.
abstract: The equilibrium [3H]estradiol binding by the partially purified estrogen receptor from calf uteri was measured at 25 degrees C. The Scatchard plot of the binding data showed a convex curve characteristic of positive cooperativity and a Hill coefficient of 1.58 +/- 0.21, at receptor concentrations of 1 to 10 nM. Below a receptor concentration of approximately 0.3 nM the Scatchard plot approached linearity, suggesting that the cooperative interactions are dependent upon a monomer--dimer equilibrium. Trypsin pretreatment of the receptor resulted in a loss of dimer formation and of the cooperative interactions. The positive cooperative characteristics of the estrogen receptor were shown not to be produced by receptor inactivation, failure to complete the [3H]estradiol--receptor equilibrium reaction, or radioimpurity of the [3H]estradiol. These findings indicate that the activated 5S estrogen receptor is a homodimer and that its formation is associated with a positive cooperative estradiol-binding reaction.
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D002417:Cattle; D005260:Female; D007700:Kinetics; D046911:Macromolecular Substances; D011485:Protein Binding; D011960:Receptors, Estrogen / Q000302:isolation & purification / Q000378:metabolism*; D013696:Temperature; D014357:Trypsin / Q000378:metabolism; D014599:Uterus / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D011960:Receptors, Estrogen; D014357:Trypsin