Trace elements selenium

A second dietary trace element, selenium, is also essential for normal thyroid hormone metabohsm. Selenium in the form of selenocysteine is a required component for three enzymes that remove iodide from thyroid hormones. Deiodination is the major metabohc pathway by which T4 and T3 are cleared from the system. After secretion by the thyroid gland, T4 may be deiodinated to yield either T3 or the physiologically inactive reverse Tj (3,3, 5 -triiodothyronine, or rX3). T3 and rTj are further deiodinated to form less active metabolites. Selenium, like iodine, is deficient in many areas of the world. 

In humans, the major pathway in the metabolism of the thyroid hormones consists of the removal of iodine or deiodination. Three deiodinase isoenzymes, encoded on three distinct genes, catalyze the reductive deiodination. All three enzymes contain the rare amino acid seleno-cysteine. The essential trace element selenium therefore plays an important role in thyroid hormone economy. 

For a long time, it was considered that, unlike the other vitamins, vitamin E had no specific functions rather it was the major Upid-soluble, radicaltrapping antioxidant in membranes. Many of its functions can be met by synthetic antioxidants however, some of the effects of vitamin E deficiency in experimental animals, including testicular atrophy and necrotizing myopathy, do not respond to synthetic antioxidants. The antioxidant roles of vitamin E and the trace element selenium are closely related and, to a great extent, either can compensate for a deficiency of the other. The sulfur amino acids (methionine and cysteine) also have a vitamin E-sparing effect. 

The trace element selenium plays an essential role in the activity of some bacterial and eukaryotic antioxidant enzymes (34). Selenium is incorporated into proteins in the form of the so-called twenty-first amino acid selenocysteine, which is encoded by a UGA stop codon. Although the chemical structure of selenocysteine differs from cysteine only by the replacement of the sulfur atom with selenium, the lower pKa of selenocysteine (5.2) allows for ionization of selenocysteine at physiological pH (35). To read through the UGA stop codon selectively, selenocysteine insertion requires a variety of proteins and RNA stmctures. 

The volcanoes of Hawaii emit large quantities of fumarolic sulfur dioxide which causes widespread damage to human health and vegetation downwind. These emissions often take the appearance of widespread hazes and are locally known as vogs. The primarily component is of sulfuric acid and sulfate formed through oxidation of the sulfur dioxide. The vog particles also contain trace elements selenium, mercury, arsenic. 

Selenium deficiency The trace element selenium is also obligatory for the normal functioning of the immunological system. Selenium deficiency has been proposed as one of the aetiological factors in PBC - although this has not yet been verified. 

In experiments in mice, the trace element selenium, which interacts with heavy metals, reduces the renal, intestinal, hepatic, and hematological toxicity of cisplatin without affecting its antitumor activity (198). 

Cell lines differ in the defined proteins they require for optimal cell growth. Usually, addition of insulin (I) and transferrin (T), along with the trace element selenium (S), is sufficient to enable most cell lines to grow in rich balanced nutrient media, such as the ones listed above. However, several categories of additives may enhance or be required for cell growth and/or production of the desired... 

Trace elements - selenium, magnesium, iron, zinc, etc. 

Brazil nuts are an excellent source of the trace element selenium, a powerful antioxidant. On average, three Brazil nuts contain 200 micrograms of selenium, which is an effective dose for helping to reduce the possibility of carcinoma, including prostate cancer. 

BAD/FER] Badiello, R., Feroci, G., Fini, A., Interaction between trace elements selenium and cadmium ions, J. Trace Elem. Med. Biol, 10, (1996), 156-162. Cited on page 275. 

Kohrle J. 1994. Thyroid hormone deiodination in target tissues - a regulatory role for the trace element selenium Exp Clin Endocrinol 102 63-89. 

This chapter will provide an overview of the factors which have been studied most extensively as potential inhibitors of cancer. It will stress data in the areas where recommendations have been made to the public (1,2). We will begin with a discussion of the macro-nutrients which have received the greatest attention for their potential for modifying cancer risk, dietary fat and fiber, and the relation of these nutrients to calorie Intake. 1 will then describe data suggesting that mlcronutrlents such as vitamins A, C, and E, and the trace element selenium, may have some potential in the inhibition of cancer. Finally, I will present some recent data in support of cancer prevention by some non-nutrient components of fruits and vegetables. 

In the determination of the trace elements, selenium, beryllium, boron, arsenic, and vanadium, all of the methods studied were found to be acceptable. 

Ferrous sulfate heptahydrate Riboflavin Sodium iodide p-Toluic acid Urea animal feed, energy source Propylene glycol animal feeds, trace element Selenium... 

While (at this writing) the details are not known, it appears that during the anaerobic growth of certain Escherichia coli bacteria, an electron transport chain of one electron oxidation-reduction processes involving quinones (cf. Chapter 8, Figure 8.11, et. seq.), the (required) trace element selenium (Se), as... 

Yeasts are capable of assimilating large quantities of the trace element selenium, mostly in a form of selenomethionine, which is easily bioavailable for humans (Rayman 2004). As a safer selenium source compared to inorganic forms, selenium-enriched yeasts were used to manufacture supplements. But currently, selenium yeasts are desirable... 

Arsenic—Although the public has long thought arsenic to be synonymous with poison, it may be less toxic than the essential trace element selenium, which it counteracts within the body. Also, recent studies on rats suggested that arsenic may be essential. 

Pyl is rare, occurring only in some ancient bacteria. Sec, containing the side chain CH2SeH, is widespread in fact, it occurs in at least two dozen human proteins that rely on the reactivity of the essential trace element selenium for their function. The pAT, for the SeH group in Sec is 5.2. (For comparison, the pATa for the SH in Cys is 8.2.) (a) Draw the structure of Sec at pH 7 compare it with that of Cys at the same pH. (b) Determine p/ for Sec. (c) Given the relationship between sulfur and selenium in the periodic table, and the pATa differences between SH and SeH, how do you expect the chemical reactivities of Sec and Cys to compare ... 

The trace element selenium is present in a number of proteins in the form of cotranslationally inserted selenocysteine (Sec). This insertion occurs when a unique selenocysteinyl-tRNA recognizes an internal UGA codon. Selenocysteine has therefore been called the 21st amino acid and its insertion at a nucleotide triplet that is normally a termination signal represents an expansion of the genetic code. 

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