title: Characterization of a [3H]methyltrienolone (R1881) binding protein in rat liver cytosol.
abstract: The binding of radiolabelled methyltrienolone 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-trien-3-one (R1881) to adult male rat liver cytosol has been characterized in the presence of Na-molybdate to stabilize steroid-hormone receptors, and triamcinolone acetonide to block progestin receptors. Using sucrose density gradient analysis, male liver cytosol contains a [3H] R1881 macromolecular complex which sediments in the 8-9S region. 8S binding of R1881 to male rat serum, female liver cytosol or cytosol from a tfm rat cannot be demonstrated. Further metabolism of [3H] R1881 following 20h incubation with male rat liver cytosol was excluded: In the 8S region 97% of [3H] R1881 was recovered by thin layer chromatography. Characteristics of this [3H] R1881-8S binding protein include high affinity (Kd = 2.3 +/- 41 nM) and low binding capacity (18.8 +/- 3.3 fmol/mg cytosol protein), precipitability in 0-33% ammonium sulfate, and translocation to isolated nuclei following in vivo R1881 treatment. Whereas, the cytosol R1881-receptor is competed for by dihydrotestosterone, testosterone, and estradiol, [3H] estradiol binding in the 8S region is not competitive with androgens but does compete with diethylstilbestrol. The nuclear androgen binding site has a Kd = 2.8 nM for [3H] R1881, and is androgen specific (testosterone greater than 5 alpha-dihydrotestosterone greater than estradiol greater than progesterone greater than cyproterone acetate greater than diethylstilbestrol greater than dexamethasone greater than triamcinolone). Since a number of liver proteins including the drug and steroid metabolizing enzymes are, in part, influenced by the sex-hormone milieu, the presence of a specific androgen receptor in male rat liver may provide valuable insight into the regulation of these proteins.
mesh_terms: D000727:Androgen-Binding Protein / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004963:Estrenes / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D015741:Metribolone; D051381:Rats; D011944:Receptors, Androgen / Q000378:metabolism; D012737:Sex Factors; D013256:Steroids / Q000378:metabolism
chemical_list: D000727:Androgen-Binding Protein; D002352:Carrier Proteins; D004963:Estrenes; D011944:Receptors, Androgen; D013256:Steroids; C488925:methyltrienolone binding protein, rat; D015741:Metribolone