PHYSICAL CHARACTERIZATION OF CORTICOSTEROID BINDERS IN ADULT-RAT HEART

The binding of natural mineralocorticoids (aldosterone, deoxycorticosterone) and natural (corticosterone, cortisol) or synthetic (dexamethasone, triamcinolone) glucocorticoids to macromolecules in adult, rat heart was analyzed by various chromatographic procedures. The GR1 component of the glucocorticoid receptor (GR) eluted in 0.001 m phosphate prewash from the DEAE-cellulose-52 columns and could be better revealed with synthetic steroids in place of natural analogues. The GR3 component could be revealed exclusively with these synthetic molecules and eluted in the 0.04 m phosphate region from the DE-52 column. The GR4 component was labelled with all natural steroids (gluco- > mineralo-) in the 0.06 m phosphate region. Both bovine serum albumin and rat serum transcortin also co-eluted with GR4. The MR1 component of the mineralocorticoid receptor (MR) in the 0.001 m prewash, and MR2 in the 0.006 m phosphate, were also observed with aldosterone and triamcinolone. The separation was less clear when chromatography was attempted on Sephadex A-25 columns, possibly because of disaggregation into subunits in the presence of high KCl concentrations required for elution. The molecular weight of receptor monomers was close to that of serum carriers on Sephadex G-200 columns, but they could be distinguished in dual-labelled chromatography. These results are discussed in terms of a heterogeneous receptor endowed with various subspecies as opposed to a unitary vector proposed by competition studies. © 1979.