[Characteristics of the steroid hormone binding system in hepatocyte plasma membranes]

Parameters of cortisone and estradiol binding to plasmatic membranes of rat hepatocytes were studied by liquid scintillation radiometry. Two systems of binding these hormones were revealed in the membranes. One of the systems is specific (saturated) and binds the hormones in physiological concentrations. The capacity and affinity of this system for cortisone is significantly higher as compared to estradiol. The parameters of binding over the temperature range of 4-37 degrees C are as follows for cortisone and estradiol, respectively: dissociation constant 2.1-3 and 2.7-4.5 nM; the number of binding sites 2.0-2.4 and 0.14-0.18 nM per one g protein. Experiments with parachlormercuribenzoate indicate participation of proteins in this system functioning. The other (unsaturated) system is nonspecific, its funtioning being determined by the lipid component of the membranes. Corticosteroid affinity for hepatocytes seems likely to be due to the functioning of the specific (saturated) system of the plasmatic membranes of these cells.