Liver Cytosol Corticosteroid Binder II, a Hormone Receptor

Abstract

Abstract Of four protein fractions previously reported which bind corticosteroids in liver cytosol, one fraction, corticosteroid Binder II, has been found to be a major hormone receptor. It has a molecular weight of 67,000 determined by gel filtration. Binder II has an appropriate glucocorticoid binding specificity: dexamethasone g corticosterone g cortisol >> cortisone >> deoxycorticosterone and it also binds progesterone and to a lesser extent the sex hormones. The Kd for dexamethasone is about 6 x 10-10 m determined in vitro and that for cortisol is in the range of 10-8 m. Binder II bound with corticosteroid is deduced to undergo nuclear transfer in vitro and in vivo as determined by its reisolation from the soluble nuclear fraction. The reisolated nucleoplasmic macromolecule has characteristics similar to corticosteroid Binder II isolated from liver cytosol (molecular weight, chromatographic elution position and pI (6.7) determined by isoelectric focusing). An antibody has been prepared to corticosteroid Binder II fraction isolated from cytosol which does not cross-react with other corticosteroid binding proteins (ligandin, Binder III and transcortin) and an antigen, determined by gel immunodiffusion, is present in the soluble nuclear fraction after nuclear transfer of macromolecular bound steroid in vitro or in vivo.