Temperature dependence of the dissociation rate constants for 8 S, 4 S, and meroreceptor forms of the estrogen receptor from rat uterus.
Conversion of a steroid receptor complex from the 8 S to the 4S form results in new interactions between the steroid and the receptor and/or formation of new intra-protein bonds within the receptor molecule itself. These bonds must be broken before the steroid is released. In order to localize these newly formed interactions, the dissociation kinetics of meroreceptors derived from 4 S and 8 S (molybdate-stabilized) receptor complexes were examined. At temperatures between 6 and 30 degrees C, no differences in the rates of dissociation were observed for the meroreceptors derived from the two forms of estrogen receptor, whereas approximately a twofold difference in dissociation rates for 4 S intact receptor versus 8 S intact receptor was detected. These findings indicate that the new interactions accompanying this conversion are likely to occur in regions of the receptor molecule other than the C-terminal portion of the steroid-binding site. The thermodynamic parameters of the dissociation reaction for the intact 4 S, and 8 S, and meroreceptor forms, respectively were: delta H [symbol; see text] = 26.2 +/- 1.3, 19.7 +/- 1.7, and 23.2 +/- 1.0 kcal/mol; +T delta S [symbol; see text] = 9.4 +/- 1.2, 3.2 +/- 1.7 and 6.6 +/- 0.9 kcal/mol (at 25 degrees C); and delta G [symbol; see text] = 16.8 +/- 2.5, 16.5 +/- 3.4, and 16.7 +/- 1.9 kcal/mol. As is the case for other steroid receptors, an increase in the enthalpy of steroid-receptor interaction after this conversion reflects the stability of the 4 S estrogen receptor complex.
Wolfson
A J
AJ
Department of Chemistry, Wellesley College, Massachusetts 02181.
Ryu
M L
ML
Baghdady
R
R
D000818:Animals; D002499:Centrifugation, Density Gradient; D005260:Female; D007700:Kinetics; D008982:Molybdenum / Q000494:pharmacology; D011487:Protein Conformation; D051381:Rats; D011960:Receptors, Estrogen / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics; D014599:Uterus / Q000187:drug effects / Q000378:metabolism*
D011960:Receptors, Estrogen; C044659:molybdate; D008982:Molybdenum