Aqueous two-phase partition studies of the glucocorticoid receptor: activation and pH-dependent changes of rat liver glucocorticoid-receptor complex in partly purified preparations.

1. The activation of the glucocorticoid receptor of rat liver cytosol was studied by the use of partitioning in an aqueous dextran-poly(ethylene glycol) two-phase system. a, Incubation unde conditions generally found to stimulate the activation results in a time-dependent increase of the partition coefficient of the glucocorticoid-receptor complex in the two-phase system. b, This increase was found to result from the fact that the activated form of the complex has a higher partition coefficient than the nonactivated one, since the two forms are eluted from DNA-Sepharose columns as clearly separated peaks with different partition coefficients, and a redistribution of complex between the peaks occurs without any changes of the partition coefficient of each single peak. c, The partition coefficient of a partly purified nonactivated complex was found to follow the same time course towards a higher value under 'activating' incubation conditions as the complex in whole cytosol. 2. The dependence of the partition coefficient of the glucocorticoid-receptor complex on the pH of the two-phase system revealed a pH-dependence of the state of the complex. Experiments with partly purified preparations of the complex showed that this change was either a conformational change or an aggregation of high affinity of the complex with itself or another DNA-binding substance.