| Abstract: | The partially purified 4.5S 3H]dihydrotestosterone receptor binds to nuclear matrix isolated from rat Dunning prostate tumor with properties similar to those reported for androgen receptor binding in intact nuclei Colvard, D.S., & Wilson, E.M. (1984) Biochemistry (preceding paper in this issue)] in that it requires Zn2+ and mercaptoethanol, is saturable, and is temperature dependent and of high affinity (Ka approximately 10(13) M-1). On a milligrams of DNA equivalent basis, the extent of matrix binding of androgen receptor (700 fmol of receptor bound/mg of matrix protein) is similar to that of intact nuclei, corresponding to approximately 1400 sites/nucleus. Association rate constants (ka) for 4.5S androgen receptor binding to matrix at 0, 15, and 25 degrees C are 2.7 X 10(5), 1.2 X 10(6), and 2.4 X 10(6) M-1 min-1, respectively, indicating an energy of activation of 15 kcal/mol. Up to 50% of matrix-bound receptor is extractable in buffer containing 3 mM ethylenediaminetetraacetic acid plus either 0.4 M KCl or 5 mM pyridoxal 5'-phosphate. A protein fraction designated 8S androgen receptor promoting factor that promotes conversion of the 4.5S androgen receptor to 8 S Colvard, D. S., & Wilson, E. M. (1981) Endocrinology (Baltimore) 109, 496-504] has been further purified and found to inhibit the binding of the 4.5S androgen receptor to isolated nuclei and nuclear matrix in a concentration-dependent manner. The results support the hypothesis that the 8S steroid receptor is a complex of the activated 4.5S androgen receptor with a non-steroid binding protein that renders the receptor incapable of binding in nuclei. |
