Physicochemical analysis of reversible molybdate effects on different molecular forms of glucocorticoid receptor

Several distinct molecular forms of glucocorticoid receptor have been identified in a melanoma model system. We have used velocity sedimentation to monitor molybdate dependent alterations in receptor size and heterogeneity. In the absence of molybdate, native glucocorticoid receptor from dexamethasone-sensitive tumors sediments at 7–8 S and 12–13 S. Under identical conditions, receptor isolated from dexamethasone-resistant tumors sediments at 7–8 S only. However, when molybdate is introduced, either during homogenization or immediately prior to centrifugation, glucocorticoid receptors from both dexamethasone-sensitive and -resistant tumors sediment sharply at 9–10 S. These molybdate induced phenomena are reversible. The activated forms of glucocorticoid receptor isolated from both dexamethasone-sensitive and -resistant tumors by DEAE-cellulose chromatography have similar sedimentation coefficients (4–5 S) which are unaffected by molybdate.