Selenocysteine-containing proteins in mammals

Since the recent discovery of selenocysteine as the 21st amino acid in prot ein, the field of selenium biology has rapidly expanded. Twelve mammalian s elenoproteins have been characterized to date and each contains selenocyste ine that is incorporated in response to specific UGA code words. These sele noproteins have different cellular functions, but in those selenoproteins f or which the function is known, selenocysteine is located at the active cen ter. The presence of selenocysteine at critical sites in naturally occurrin g selenoproteins provides an explanation for the important role of selenium in human health and development. This review describes known mammalian sel enoproteins and discusses recent developments and future directions in the selenium field.