[A special estrogen-binding protein of the liver: additional data on the structural determinants of androgenic ligands].

The relative competitive activity of some androstane derivatives was determined by 50% inhibition of [3H]estradiol binding to an unusual estrogen-binding protein (UEBP) of male rat liver. It was shown that: i) the bulk of energy of the steroid-protein complex is derived from hydrophobic interactions; ii) the authentic ability to form specific complexes with UEBP at androgene concentrations close to physiological ones, is determined by 17 beta-hydroxyl and is enhanced by the 3 alpha- or 2 alpha-oxy-group; iii) 3- and 17-keto groups inhibit androgene interaction with UEBP; iiii) the cis-conjunction of rings A and B in the androgen molecule does not block steroid binding to the protein. These data specify significantly the mechanism of androgene interaction with UEBP and shed additional light on the physiological role of this protein.