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Temperature‐Dependent Kinetic Correlates of the Activation of the Glucocorticoid‐Receptor Complex

Abstract: The effects of temperature on the kinetics of activation were studied in [3H]triamcinoIone acetonide([3H]TA)‐labeled cytosol preparations from mouse whole brain. After removal of unbound [3H]TA and molybdate (which prevents activation) from the unactivated steroid‐receptor complex by gel exclusion chromatography, activation was initiated by incubation at 6–30°C for 0.75–24 min and then rapidly quenched at –5°C with Na2MoO4 (20 mM final concentration). The loss of the 9.2S (unactivated) form of the [3H]TA‐receptor complex and the concomitant formation of the 3.8S (activated) form increased dramatically with increases in the activation temperature. These hydrodynamic changes were correlated directly with rapid time‐ and temperature‐dependent increases in the binding of [3H]TA‐labeled cytosol to DNA‐cellulose (DNA‐C). Further analyses of these data revealed a >50‐fold increase in the apparent first‐order rate constant for the increased binding to DNA‐C as the activation temperature was increased from 6°C to 30°C. An Arrhenius plot of these temperature‐dependent kinetic constants revealed an energy of activation of 116 kJ. These data support a proposed model for activation of the glucocorticoid‐receptor complex that includes the splitting of a 297 kDa, unactivated species into a 92 kDa, activated species.