Stereospecific binding of aldosterone to renal chromatin.

In an earlier study, 51% of total renal nuclear content of 3H-aldosterone was recovered bound to nuclear proteins readily extractable with Tris-3 fll~ CaC12. Modifications iu the methods used to prepare renal nuclear fractions resulted in the isolation of 3H-aldosterone bound to chromatin to the extent of 55% of the total nuclear content of the steroid. The chromatin binding system was stereospecific for aldosterone and related mineralocorticoids. In competition studies, the order of affinities for the 3H-aldosterone binding sites was d-aldosterone > 9cr-fluorocortisol > cortisol > 17a-estradiol ” progesterone = 17cy-isoaldosterone. Actinomycin D did not compete for the 3H-aldosterone binding sites in renal chromatin. The binding affinities were in accord with the relative potencies of these steroids as mineralocorticoids. In addition, spirolactone blocked the binding of 3H-aldosterone to chromatin at the molar ratio needed to block the action of the steroid on sodium transport. Based on differential susceptibility to specific hydrolases (i.e. DNase, RNase, trypsin, and chymotrypsin), CsCl density centrifugation, chemical analysis of 0.3 M KC1 extracts of labeled chromatin, and glycerol density centrifugation, the primary binding unit appears to be a 4 S, nonhistone chromosomal protein. The aldosterone-binding protein is heatlabile and tends to be stabilized by 20% glycerol. The possibility that the formation of the aldosterone-chromosomal binding system initiates steroidal action on active sodium transport is discussed.