Selenium, biological role

Unlike selenium there is no required biological role for tellurium in bacteria or plants that has been determined however, this may ultimately not be the whole story.111 Selenium was only viewed as a toxic metalloid with no necessary role for metabolism until at least the 1950s see above. While tellurite is less soluble than tellurate in aqueous solution, in general tellurite is probably more toxic to most organisms.190 The non Te-resistant wild type E. coli bacterium (Gramnegative) has MICs of 1 to 3 ppm for tellurite and tellurate.144,191,192 Tellurite is used to enrich and select for Staphylococcus aureus.169,193,194... 

Formate dehydrogenase O is present in E. coli cells grown aerobically or anaerobically in the presence of nitrate. It is the least well-studied of the three isoenzymes, although it is this system for which a biological role of the element selenium was first demonstrated. Formate dehydrogenase O appears to act as an oxidoreductase coupling formate oxidation with quinone reduction, but a detailed analysis of its structure and redox partners has not yet been carried out. 

The elements of groups 13—16 fall into three categories (Fig. 1.3), the metalloids, the other metals, and the nonmetals. The important biological role of some of the nonmetals, oxygen, nitrogen, phosphorus, sulfur, and selenium together with the halogens, chlorine and iodine, will be discussed in Chapter 18. 

Hatfield, Dolph L., Marla J. Berry, and Vadim N. Gladyshev, eds. Selenium Its Molecular Biology and Role in Human Health. Dordrecht, The Netherlands Kluwer Academic Publishers, 2001. This book explains recent advances in the understanding of selenium s role in the human body. 

Due to the biological role of selenium (see below), the element is used in pharmaceutical applications, as a supplementary additive for grazing ground and as an additive in anti-dandruff shampoos. 

The periodic table shown highlights the essential elements in the human body. Of special interest are the trace elements, such as iron (Fe), copper (Cu), zinc (Zn), iodine (I), cobalt (Co), selenium (Se), and fluorine (F), which together make up about 0.1 percent of the body s mass. Although the trace elements are present in very small amounts, they are crucial for our health. In many cases, however, their exact biological role is still not fully understood. 

The quality of the experimental evidence for nutritional essentiality varies widely for the ultratrace elements. The evidence for the essentiality of three elements, iodine, molybdenum and selenium, is substantial and noncontroversial specific biochemical functions have been defined for these elements. The nutritional importance of iodine and selenium are such that they have separate entries in this encyclopedia. Molybdenum, however, is given very little nutritional attention, apparently because a deficiency of this element has not been unequivocally identified in humans other than individuals nourished by total parenteral nutrition or with genetic defects causing disturbances in metabolic pathways involving this element. Specific biochemical functions have not been defined for the other 15 ultratrace elements listed above. Thus, their essentiality is based on circumstantial evidence, which most often is that a dietary deprivation in an animal model results in a suboptimal biological function that is preventable or reversible by an intake of physiological amounts of the element in question. Often the circumstantial evidence includes an identified essential function in a lower form of life, and biochemical actions consistent with a biological role or beneficial action in humans. The circumstantial evidence for essentiality is substantial for arsenic, boron, chromium, nickel, silicon, and vanadium. The evidence for essentiality for the... 

The importance and understanding of selenium s role in nutrition, and the development of industrial uses have made selenium an important metalloid and it is now a significant element industrially, biologically and also environmentally. 

Hansen D., Duda P.J., Zayed A. Terry N. Selenium removal by constructed wetlands role of biological volatilization. Environ Sc Technol 1998 32 591-597. 

The vast majority of research focused on selenium in biology (primarily in the fields of molecular biology, cell biology, and biochemistry) over the past 20 years has centered on identification and characterization of specific selenoproteins, or proteins that contain selenium in the form of selenocysteine. In addition, studies to determine the unique machinery necessary for incorporation of a nonstandard amino acid (L-selenocysteine) during translation also have been central to our understanding of how cells can utilize this metalloid. This process has been studied in bacterial models (primarily Escherichia colt) and more recently in mammals in vitro cell culture and animal models). In this work, we will review the biosynthesis of selenoproteins in bacterial systems, and only briefly review what is currently known about parallel pathways in mammals, since a comprehensive review in this area has been recently published. Moreover, we summarize the global picture of the nonspecific and specific use of selenium from a broader perspective, one that includes lesser known pathways for selenium utilization into modified nucleosides in tRNA and a labile selenium cofactor. We also review recent research on newly identified mammalian selenoproteins and discuss their role in mammalian cell biology. 

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