Competitive binding studies with glucocorticoid receptors from rat-thymus cells: differential temperature-dependence of steroid binding.
Competitive steroid-binding studies were performed with intact rat thymus cells and with cytosol preparations at different temperatures using [1,2-3H]dexamethasone as the labelled ligand. Steroids lacking a 17 alpha-hydroxyl group, such as corticosterone, were better able to compete with [1,2-3H]dexamethasone for binding to glucocorticoid receptors at 0 degrees C than compounds containing a 17 alpha-hydroxyl substituent, such as cortisol. At 37 degrees C the reverse was true. This temperature-dependent change in relative affinities appeared to be unrelated to steroid metabolism or receptor activation, and to depend only on the thermodynamic parameters of the steroid--receptor interaction. Relative biological activities for different steroids agree more closely with the relative affinities determined at 37 degrees C than with those determined at lower temperatures.
D000818:Animals; D001667:Binding, Competitive; D003345:Corticosterone / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000187:drug effects / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*; D013696:Temperature; D013950:Thymus Gland / Q000378:metabolism*
D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; D003907:Dexamethasone; D003345:Corticosterone