Glucocorticoid receptors in cytosol and nuclear extract of human leukocytes.

Cortisol binding by cytosol and 0.4 M KCl extract of the nuclear fraction of human leukocytes were studied by gel chromatography and ion exchange filtration on DEAE cellulose. The cytoplasmic cortisol binding protein has a molecular weight 95 000 and the soluble nuclear binding protein 50 000. The absence of the uptake of radioactive cortisol by isolated nuclei and the apparent requirement of the cytosol for glucocorticoid specific binding in nuclear receptor sites was observed. The association constant characterising the binding of cortisol to cytosol was KA = 3.5 . 10(9) l/mol.