Accurate determination and physicochemical properties of rat liver nuclear retinoic acid (RA) receptors.

The present study was undertaken to establish a novel in vitro method for quantitative determination of the nuclear RA receptors in rat liver. Binding characteristics of RA receptors (free of any contaminating cytoplasmic proteins), in relation to various physicochemical conditions, were evaluated. Three different binding sites for all-trans RA were found in nuclear proteins of rat liver. One of them represents a high affinity and low capacity RA specific binding site with Ka1 0.687 +/- 0.294 x 10(9) M-1 and the Bmax1 0.644 +/- 0.397 pmol/mg protein. Others represent low affinity and high capacity RA non-specific binding sites with Ka2 2.694 x 10(6) M-1; Bmax2 225 pmol/mg protein and Ka3 0.131 x 10(6) M-1; Bmax3 1125 pmol/mg protein, respectively.