Selenium is well-known as a toxic substance. However, it has also been found to be an essential mineral. That is, too little you die and too much you die. Arsenic is toxic as well but, surprisingly, the toxic effects of selenite and arsenite are mitigated when taken together. The chemical basis for this surprising result will be discussed. Since selenium is an essential mineral, selenium supplementation is most safely administered with selenized yeast. It has also been reported that selenized yeast can decrease the onset of lung, prostate and colorectal cancer and numerous other afflictions. Consequently, elucidation of the chemical form of selenium in selenized yeast is important. Efforts to determine the chemical speciation of selenium in selenized yeast will be presented. It has been found that selenocysteine is a rare but important component in a variety of proteins including enzymes in which it is present at the active site. Selenocysteine is not formed by post-translational modification; it is incorporated cotranslationally rendering it the 21st such amino acid. Selenophosphate plays a key role in this process and its chemical synthesis and reactions will be presented.

Selenium: From poison to the 21st amino acid

251st National Meeting (2016)

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