Selenium is an essential trace element in the diet of humans and many other life forms. As discussed in this book, selenium plays an important role in preventing certain forms of cancer, heart disease and other cardiovascular and muscle disorders. Evidence points to numerous other health benefits including an indispensable function in development, male reproduction and the immune system. In addition, selenium serves as an antiviral agent and may delay the onset of AIDS in HIV positive patients and delay the aging process. This element occurs primarily in cellular proteins in the form of a novel amino acid selenocysteine. Selenocysteine is the 21st amino acid in the genetic code and is cotranslationally incorporated into protein in response to the codon, UGA. Selenoproteins control redox homeostasis and are involved in variety of cellular pathways. The emphasis of this book is on the current status of the molecular biology of selenium. The importance of this element in human health is also highlighted.

Zusammenfassung
The discovery of selenoproteins in 1973 was the starting point for today's flourishing selenium field [1,2]. It provided evidence that selenium had biochemical functions that could account for its nutritional effects [3,4]. Further, it opened the selenium field to investigation by the methods of biochemistry, which led to the identification of several more selenoproteins and showed that selenocysteine was the form of the element in animal selenoproteins and in most bacterial ones. Although noteworthy efforts were made to uncover the mechanism of selenocysteine and selenoprotein synthesis using biochemical methods, the problem yielded only when attacked with the methods of molecular biology [5,6]. The bacterial mechanism was characterized first; characterization of the animal mechanism is a work in progress. It is interesting to note that the only genes that are devoted to selenium metabolism are those that support selenoprotein synthesis and selenocysteine catabolism. Consequently, it seems likely that competition for selenium between selenoprotein synthesis and the production of selenium excretory metabolites [7] controls who- body selenium homeostasis. The physiological functions of selenium derive fi-om the catalytic and physical properties of selenoproteins. Selenoproteins such as the glutathione peroxidases and the thioredoxin reductases have redox activities that allow them to serve in oxidant defense. The deiodinases use their redox activities to activate and inactivate thyroid hormones. From these two examples, it can be seen that selenoprotein functions are diverse while having in common a redox mechanism.

Inhalt
Selenium: A historical perspective.- Selenium: A historical perspective.- Biosynthesis of selenocysteine and its incorporation into protein.- Selenium metabolism in prokaryotes.- Mammalian and other eukaryotic selenocysteine tRNAs.- Evolution of selenocysteine decoding and the key role of selenophosphate synthetase in the pathway of selenium utilization.- SECIS RNAs and K-turn binding proteins. A survey of evolutionary conserved RNA and protein motifs.- SECIS binding proteins and eukaryotic selenoprotein synthesis.- The importance of subcellular localization of SBP2 and EFsec for selenoprotein synthesis.- Selenocysteine biosynthesis and incorporation may require supramolecular complexes.- Selenium-containing proteins.- Selenoproteins and selenoproteomes.- Deletion of selenoprotein P gene in the mouse.- Selenium and methionine sulfoxide reduction.- Selenoprotein W in development and oxidative stress.- The 15-kDa selenoprotein (Sep15): functional analysis and role in cancer.- Regulation of glutathione peroxidase-1 expression.- Selenoproteins of the glutathione system.- New roles of glutathione peroxidase-1 in oxidative stress and diabetes.- Selenoproteins of the thioredoxin system.- Mitochondrial and cytosolic thioredoxin reductase knockout mice.- Selenium, deiodinases and endocrine function.- Biotechnology of selenocysteine.- Selenium and human health.- Selenium, selenoproteins and brain function.- Selenium as a cancer preventive agent.- Peering down the kaleidoscope of thiol proteomics and unfolded protein response in studying the anticancer action of selenium.- Genetic variation among selenoprotein genes and cancer.- Selenium and viral infections.- Role of selenium in HIV/AIDS.- Effects of selenium on immunity and aging.- Selenium and male reproduction.- Mouse models for assessing the role of selenoproteins in health and development.- Drosophila as a tool for studying selenium metabolism and role of selenoproteins.- Selenoproteins in parasites.- Incorporating 'omics' approaches to elucidate the role of selenium and selenoproteins in cancer prevention.- Selenium-induced apoptosis.- Selenoprotein mimics.- Update of human dietary standards for selenium.