Recent developments in selenium metabolism and chemical speciation: A review

The biological roles of selenium and its mode of action have only recently begun to be revealed. To date, the major functions of selenium can be attri buted to its antioxidative properties and its role in the regulation of thy roid hormone metabolism, cell growth and eicosanoid biosynthesis. The unusu al feature of selenoprotein synthesis is that selenocysteine insertion is s pecified by the stop UGA codon. A number of selenocysteine-specific gene pr oducts and a stem-loop structure in the 3' untranslated region are required for selenocysteine biosynthesis and the decoding of UGA codons in the open reading frame of the mRNA. The major biological functions of selenium are achieved through its redox activity when present as selenocysteine at the a ctive sites of selenoproteins and these proteins are selenium-dependent sin ce replacement with the sulphur analogue cysteine causes loss of enzyme act ivity. Both organic and inorganic forms of selenium may be utilised by the body, with the selenoamino acids showing greatest bioavailability. Knowledg e of the biochemistry of the element coupled with appropriate techniques fo r the study of the distribution of selenium species in health and disease c ould help to identify sensitive markers of selenium status.