Molybdate permits resolution of untransformed glucocorticoid receptors from the transformed state

The presence of 10 mM sodium molybdate has a profound effect on the physical behavior of glucocorticoid receptors submitted to ammonium sulfate precipitation or to DEAE-cellulose chromatography. Molybdate inhibits the inactivation of the unoccupied receptor and prevents the transformation of the steroid-bound receptor that occurs when rat liver cytosol is precipitated with ammonium sulfate. The transformed glucocorticoid . receptor complex is precipitated at 30 to 35% ammonium sulfate, whereas the unoccupied receptor and the untransformed steroid-bound receptor are precipitated at 45 to 55% of ammonium sulfate saturation. The untransformed steroid . receptor complex precipitated at 45 to 55% ammonium sulfate saturation in the presence of molybdate can undergo temperature-mediated transformation when it is redissolved in buffer without molybdate. The presence of molybdate in both the loading buffer and eluting gradient during DEAE-cellulose chromatography prevents the transformation of steroid-bound receptor to a less negatively charged, DNA-binding state which otherwise occurs during the chromatographic procedure. In the presence of molybdate, DEAE-chromatography yields a 33-fold purification of the untransformed steroid . receptor complex.