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 17α-hydroxyl group, such as corticosterone, were better able to compete with [1,2-3H]dexamethasone for binding to glucocorticoid receptors at 0°C than compounds containing a 17α-hydroxyl substituent, such as cortisol. At 37°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°C than with those determined at lower temperatures. © 1979.