title: Kinetics of dexamethasone binding to the glucocorticoid receptor of intact erythroid cells from rat fetal liver.
abstract: The erythroid cells from the rat fetal liver have been shown to possess a receptor for glucocorticoids. In the present work, the characteristics of [3H]dexamethasone binding have been studied on intact cells, in order to minimize receptor degradation, and at 4 degrees C, in order to prevent the activation of the hormone-receptor complex. Dissociation kinetics were those of a first-order reaction and the value of the rate constant of dissociation was similar to the values available in the literature. When studied at low concentrations of the ligand and using short-term incubations, association kinetics were apparently those of a simple bimolecular reaction. But at high ligand concentrations and/or using long-term incubations, association kinetics indicated a more complex reaction. Our results were compatible with the model proposed by Pratt W.B., Kaine J.L. and Pratt V.D. (J. Biol. Chem. 250 (1975) 4584-4591) for cytosolic preparations. This model implies the rapid formation of a transient unstable form of the complex, further converted into a stable form with slower kinetics. Equilibrium dissociation constant of the first (rapid) reaction was 80 microM and the rate constant of 'stabilization' was of the order of 70 X 10(-3) min-1. These values agree with the results of Pratt et al. relative to a cytosolic preparation from rat thymocytes.
mesh_terms: D000818:Animals; D003907:Dexamethasone / Q000378:metabolism*; D004900:Erythroblasts / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D008099:Liver / Q000166:cytology* / Q000196:embryology; D008433:Mathematics; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*
chemical_list: D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; D003907:Dexamethasone