Effects of dietary selenium on the tissue concentrations of type I iodothyronine 5'-deiodinase and other selenoproteins.

Since selenium was identified as the essential component of the type I iodothyronine 5'-deiodinase, it has become important to determine the selenium dose necessary for the formation of the deiodinase. In this survey the results of studies of the effects of dosage and chemical form of the element on the concentrations of this enzyme and of other selenoproteins are discussed. They show that the selenium requirement for normal deiodinase activity is lower than it is for adequate glutathione peroxidase activity. Elevated tissue selenium concentrations found after intake of higher doses of the element, especially when given in the form of selenomethionine, are due to nonspecific incorporation into other proteins. The tissue concentrations of the selenonenzymes appear to be homeostatically controlled and cannot be further increased by additional selenium supplementation.