Effect of heat treatment on the glucocorticoid-receptor complex dependence on steroid structure

Abstract

The Arrhenius plot of heat inactivation of the rat liver glucocorticoid receptor protein gave a straight line with ΔH + + = 115 kJ/mol over the 0–44°C range. Molybate ions were considerably protective but did not affect the linearity or slope of the Arrhenius plot. The effect of triamcinolone acetonide on heat stability of the receptor was similar to that of molybdate. On the other hand, glucocorticoid antagonists, although bound to the receptor, did not protect it from heat inactivation. Incubation of the complex of the glucocorticoid receptor with optimal glucocorticoids under activating conditions (elevated temperature or ionic strength) resulted in a considerable decrease in the dissociation rate. However, if the complex was incubated at 25°C in the presence of molybdate, its dissociation rate did not change. Heat treatment without molybdate of complexes of gluococorticoid antagonists did not decrease the dissociation rate. These findings indicate that the decrease in dissociation rate is probably related to nucleophilic transformation. An 11β-hydroxyl group in the steroid structure seems to be an absolute requirement both for protection of the receptor against heat inactivation and for stabilization of the complex under conditions that promote neucleophilic transformation.