Mammalian selenium-containing proteins.

Mammalian selenium-containing proteins can be divided into three groups: proteins containing nonspecifically incorporated selenium, specific selenium-binding proteins, and specific selenocysteine-containing selenoproteins. Selenoproteins with known functions identified so far include five glutathione peroxidases, two deiodinases, several thioredoxin reductases, and selenophosphate synthetase 2. Alternative splicing leads to a greater variety of selenoproteins, as was shown in the cases of a specific sperm nuclei glutathione peroxidase and some thioredoxin reductases. Selenoprotein P, selenoprotein W, a 15-kDa selenoprotein, an 18-kDa selenoprotein, and several selenoproteins identified in silico from nucleotide sequence databases were found to contain selenocysteine but their functions are not known. Gel electrophoretic separation of tissue samples from rats labeled in vivo with (75)Se showed the existence of further selenium-containing proteins.