Selenium and selenoproteins in the rat kidney

Kidney tissue contains a high concentration of selenium that is not accounted for by the known selenoprotein glutathione peroxidase (glutathione: hydrogen-peroxide oxidoreductase, EC 1.11.1.9). In order to investigate the nonglutathione peroxidase selenium, rats were isotopically labeled with [75Se]selenite over a 10-day period. After this time half of the 75Se in kidney homogenate was found in the particulate subcellular fractions. The kidney lysosomes contained unusually high levels of 75Se, yet they did not contain correspondingly high levels of glutathione peroxidase activity. Two selenoproteins having molecular weights less than 40 000 were resolved by gel filtration from a kidney supernatant fraction. A third selenoprotein exhibited a molecular weight of 75 000. This protein contained one 75 000 molecular-weight subunit, and its selenium was in the amino acid selenocysteine. The 75 000 molecular-weight protein was chromatographically distinct from glutathione peroxidase. In order to determine if these selenoproteins protect against cadmium toxicity, 109CdCl2 was administered to rats that were isotopically prelabeled with 75Se. At 3, 25 and 72 h after 109Cd administration, no 109Cd was associated with selenium-containing proteins. Two of the nonglutathione peroxidase selenoproteins were apparently unique to the kidney.