SELENOPROTEINS FROM RAT TESTIS CYTOSOL

Radioactive inorganic selenium, administered intraperitoneally at 1 mg/kg body weight to young adult rats, acculumulates in testes for 7 days or longer, whereas liver, kidney and serum levels fall more rapidly. 3-4 h after administration of [75Se]selenite, 55-60% of the radioactivity in the testes was found in the cytosol, associated with protein. Ultragel ACA-22 chromatography of testis cytosol prepared 4 h after 75Se treatment revealed a major selenoprotein having an apparent molecular weight of 59 000. Sodium dedecyl sulfate polyacrylamide gel electrophoresis indicated extensive heterogeneity of radioactivity with apparent molecular weights of about 57 000 and 45 000 and 15 000. Cytosol from rats treated 4 weeks earlier showed predominance of the 15 000 molecular weight [75Se]selenoprotein. Sucrose density gradient ultracentrifugation at either low or high ionic strength demonstrated a single 7 S selenoprotein. Chromatography with Blue-Sepharose indicated that the radioactivity was not associated with albumin. Strong 75Se binding to protein was demonstrated by overnight dialysis against water, 2 M NaCl, β-mercaptoethanol, 8 M urea, selenite. However, 85% of the 75Se was removed by dialysis against 0.5 M NaOh. This stability contrasts with the lability of disulfide reagents of selenite-protein complexes formed in vitro. The fact that selenium is incorporated in substantial amounts into a discrete and stable protein suggests a physiological role for this essential trace element in the testes. © 1979.