9S binding protein for androgens and progesterone.
A steroid binding protein fraction with a sedimentation coefficient of approximately 9 S (molecular weight approximately equal to 200,000) has been identified in 105,000 X g supernatants of several androgen-responsive organs. Highest concentrations were found in epididymis and testis, but small amounts were detected in prostate, seminal vesicle, kidney, submandibular gland, and lung. The 9S protein binds [3H]dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one) and [3H]progesterone (4-pregnene-3,20-dione) with equilibrium binding constants of approximately 10(5) M-1 and 10(6) M-1, respectively. The concentration of 9S binding sites in epididymis is approximately 10(-11) mol/mg of supernatant protein, which is at least 10(5) times greater than the concentration of androgen receptor. 9S binding protein appears to be a nonsecretory, intracellular protein and has properties different from the andorgen receptor. It is unretarded on DEAE-Sephadex chromatography at pH 8.0, and its sedimentation rate on sucrose gradients is not altered at high ionic strength (0.4 M KCl). Like the androgen receptor, its binding activity, which is maximal between pH 7 and 9.5, is heat labile, decreased by sulfhydryl reagents, and enhanced by 2-mercaptoethanol. It is suggested that because of its high concentration and low affinity, 9S binding protein may function in the intracellular accumulation of compartmentalization of androgens or progesterone.
D015113:Androstane-3,17-diol / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002352:Carrier Proteins / Q000302:isolation & purification*; D002369:Castration; D003600:Cytosol / Q000378:metabolism; D013196:Dihydrotestosterone / Q000378:metabolism*; D004822:Epididymis / Q000378:metabolism*; D004958:Estradiol / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007016:Hypophysectomy; D007700:Kinetics; D008297:Male; D008623:Mercaptoethanol / Q000494:pharmacology; D008970:Molecular Weight; D011374:Progesterone / Q000378:metabolism*; D051381:Rats; D013737:Testis / Q000378:metabolism*
D002352:Carrier Proteins; D013196:Dihydrotestosterone; D015113:Androstane-3,17-diol; D011374:Progesterone; D004958:Estradiol; D008623:Mercaptoethanol