[Hormonal specificity of the affinity of specific estrogen-binding protein in the rat liver].

The ability of 57 steroids and their analogs to compete with 3H-estradiol for binding sites of an unusual estrogen-binding protein (UEBP) of the male rat liver was studied. The magnitudes of the equilibrium constants of association of 3H-estradiol, 3H-estriol, and 3H-5 alpha-androstane-3 alpha, 17 beta-diol with the UEBP were measured. It was shown that the derivatives of estrane and androstane, in contrast to those of pregnane, stilbene and triphenylethane, can effectively interact with the UEBP. The ability of estrogens and androgens to interact with the UEBP primarily depends on oxygen functions of the A and D rings and on general conformation of the steroid molecule. It is suggested that there are 2 subcenters for the steroid A and D rings both at the estrogen and androgen sites of the UEBP molecule. These subcenters for the two types of sex steroids either do not coincide or coincident are only subcenters for the ligand A rings.