[Interaction of the transcortin-progesterone complex with plasma membranes of human decidual epithelium]

It was demonstrated that transcortin complexed with progesterone specifically binds to plasma membranes of human decidual endometrium, a progesterone target tissue. This interaction is characterized by a high affinity [Kd = (1.0 +/- 0.2).10(-10) mol/l] and selectivity. Such human serum proteins as albumin, orosomucoid, transferrin, thyroxine- and sex steroid-binding globulins do not compete with transcortin for the binding sites on the membranes. The concentration of endogenous transcortin in sodium cholate-solubilized endometrium cell membranes was determined by the radioimmunoassay method.