Mammals selenium

Marine mammals collected near heavily urbanized or industrialized areas or near zinc pollution point sources usually had elevated zinc concentrations when compared to individuals of the same species and of similar age from relatively pristine environments (Eisler 1984). Zinc concentrations in tissues of the ringed seal (Phoca hispida) were essentially the same in animals near a lead-zinc mine and in those of a distant reference site, although lead and selenium burdens were elevated in the vicinity... 

Adults fed diets for 11 weeks containing 5 or 9 mg Se/kg DW ration as seleno-L-methionine or naturally incorporated selenium (mammals from Kesterson National Wildlife Refuge, California)... 

Clark, D.R. Jr. 1987. Selenium accumulation in mammals exposed to contaminated California irrigation drainwater. Sci. Total Environ 66 147-168. 

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. 

The stem-loop structure in the noncoding 3 region of selenoprotein mRNAs has also been termed a SECTS element in mammals although it has a different overall structure. ° In silica analysis of the human genome sequence, using this consensus SECTS element along with the presence of the characteristic UGA codon within an exon, has led to the discovery of several new selenoproteins, including a selenium-dependent methionine sulfoxide reductase. It has been shown that a specific complex exists for selenoprotein synthesis that shuttles between the nucleus and the cytosol. This possibly protects the preformed complex for nonsense-mediated decay to allow for more efficient selenoprotein synthesis. The specific tRNA needed for selenocysteine... 

Glutathione peroxide was the first selenium-containing mammalian enzyme identified over 35 years ago," the same year that the selenoprotein A was identified in C. sticklandtL With the advent of the human genome sequence we now know that there are 25 selenoproteins encoded in humans, " with similar numbers encoded by other mammals. Some of the best-studied selenoproteins include five isoenzymes of thioredoxin reductase, three... 

In contrast to selenium, the methylated products of tellurium are considered more toxic for mammals. 

In a number of reproductive studies in mammals, using a variety of selenium compounds, adverse effects have only been seen at doses that are associated with maternal toxicity "... 

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