ABSTRACT
Selenium (Se) was discovered by the Swedish chemist, Jakob Berzelius, in 1817. Its name comes from the Greek word for moon, selene. It is a group VIA metalloid with an atomic weight of 78.96. Se shares many similar chemical properties with sulfur (S), although the Se atom is slightly larger. Similar to S, Se can exist in ve valence states, selenide (2−), elemental Se (0), thioselenate (2+), selenite (4+), and selenate (6+). Se was originally identi ed as a potentially toxic element long before it was recognized to be an essential micronutrient for animals and humans. Se salts are toxic in large amounts, but trace amounts of the element are necessary for cellular function. In 1973, Se was shown to form part of the important antioxidant enzyme, glutathione (GSH) peroxidase. It takes part in forming the active center of the enzymes, glutathione peroxidase and thioredoxin reductase, which indirectly reduce certain oxidized molecules and three known deiodinase enzymes that convert one thyroid hormone to another in most, if not all, animals.
