Selenium is incorporated into proteins in the form of selenocysteine. These proteins containing selenocysteine (Sec) are termed selenoproteins. Selenoproteins are present in all lineages of life (i.e., bacteria, archaea, and eukarya).
Families of selenoproteins include the glutathione peroxidases, the iodothyronine deiodinases and the thioredoxin reductases.
Selenoproteomes among species are generally small; the largest repertoire exists in fish with 30 individual selenoproteins, followed by humans and rodents with 25 and 24 selenoproteins, respectively.
Selenoproteins have biological functions in oxidoreductions, redox signaling, antioxidant defense, thyroid hormone metabolism, and immune responses.
Approximately 10 additional selenoproteins have been identified. One of them, selenoprotein P, is an extracellular protein that contains most of the selenium in plasma. It associates with endothelial cells, probably through its heparin-binding properties.
Selenoproteins
