Specific cytosol binding of diethylstilbestrol in rat skeletal muscle

Rat skeletal muscle cytosol proteins bound 3H-diethylstilbestrol (3H-DES). More than 90% of this binding was high capacity and low affinity. Serum albumin accounted for roughly 50-60% of the binding, as evidenced by its precipitation with anti-rat albumin IgG. About half of the binding was distinguishable from albumin and other serum proteins by its precipitation in 40% saturated ammonium sulfate. This material sedimented at 4-5S in high-salt sucrose gradients, and resolved into two components (8S and 4-5S) in low-salt. Following incubation at 23-27 degree C for one hour, 2% of the bound 3H-DES in whole cytosol (approximately 2 fmole/Mg cytosol protein) was retained by DNA cellulose, and was eluted with 0.6 M KCl. This small fraction of the total binding was inhibited by estrogens and DES analogues: estradiol-17 beta, DES, dienestrol, and hexestrol were strong inhibitors; isodienestrol, dimethylstilbestrol, estradiol-17 alpha, estrone, tamoxifen, MER-25, CI-628, and nafoxidine were weak inhibitors; dihydrotestosterone, testosterone, and prednisone did not compete. These observations indicate that specific estrogen-binding sites exist in rat skeletal muscle.