[Identification of receptors in a system of functionally heterogeneous proteins specifically bound to androgens in rat liver cytosol].

The methods of androgen receptor (RA) isolation and identification in rat liver cytosol were studied. It was shown that male rat liver contains a system of specific androgen (A)-binding proteins consisting of at least three main components: RA, delta 4-androstendione (delta 4-A)-binding component and an unusual estrogen-binding protein interacting also with A and the first two components in females. The identity of one of A-binding components to RA was proved by cumulative properties of this component which are similar to those of RA from other tissues. These properties are as follows: 1) high values of apparent association constant, Ka, for 3H-R1881 (2.8 +/- 0.3 X 10(8) M-1) and 3H-5 alpha-dihydrotestosterone (3H-DHT) (5.0 +/- 0.4 X 10(8) M-1); 2) low binding capacity--approximately 10 fmol/mg of protein of nonfractionated cytosol; 3) pronounced specificity of affinity for active A (DHT, R1881, testosterone); 4) large size of the protein molecule (6.5 +/- 0.25 nm); 5) ability to decrease this size to 3.2 +/- 0.08 nm in a high ionic strength buffer; 6) precipitation at low concentrations of ammonium sulfate: 7) strong interaction with heparin-Sepharose. The properties of the delta 4-A-binding component do not coincide with those of RA: it has a low Ka for 3H-delta 4-A (1.15 +/- 0.5 X 10(6) M-1), a high binding capacity (1.22 +/- 0,12 pmol/mg of protein of nonfractionated cytosol) and can bind various delta 4-3-ketosteroids irrespective of the degree and nature of their biological activity. It was concluded that preliminary isolation of rat liver RA on heparin-Sepharose can be used for differential identification and characterization of this protein.