SELENIUM-DEPENDENT GLUTATHIONE-PEROXIDASE AND OTHER SELENOPROTEINS - THEIR SYNTHESIS AND BIOCHEMICAL ROLES

Selenium-dependent glutathione peroxidase (SeGPX, EC 1.11.1.9) acts as part of the antioxidant defence of the body. It functions as a highly efficient catalyst to reduce a wide variety of intracellular peroxide s, including hydrogen and lipid peroxides, thereby detoxifying these p otentially damaging molecules. Thus selenium has a critical role in no rmal cellular biochemistry and the proposal has been made that deficie ncy of selenium in the diet can lead to a number of clinical disorders . World-wide interest in selenoproteins is now evident. In general, th e active site of SeGPX and of other selenoproteins is based upon a sel enium moiety (generally a single covalently bound atom of selenium) pr esent as the amino acid selenocysteine. There has been an extension of the genetic code to include the codon TGA (in the correct DNA context ) as the 21st codon specifying the presence of selenocysteine in the p olypeptide structure of selenoproteins. Recent discoveries in SeGPX bi ochemistry and molecular biology in relation to its protective functio n are reviewed here in comparison to other selenoproteins. The mechani sms of selenium incorporation into selenoproteins is also described. I n the future, antioxidant enzymes such as selenium-dependent glutathio ne peroxidase may find a use in biotechnology for the protection of en zymes and cellular membranes. While it is recognised that in cost term s the use of enzyme mimics of SeGPX may be more advantageous, large-sc ale in-vitro production of the selenoproteins is now possible and thei r value can be readily assessed.