Selenomethionine

As with selenocystine, the amino acid selenomethionine, CH3Se(CH2)2CH(NH2)COOH, is largely incorporated into proteins but has been found in the free form to some extent. Onions Allium cepa) which had been injected with radioactive selenite were reported to contain selenomethionine as were ethanol extracts of red clover, white clover and rye 

DL-Selenomethionine was initially synthesized by Painter via a sodium/liquid ammonia reduction of DL-selenohomocystine followed by an alkylation of the resulting sodium selenohomocysteinate with methyl iodide. Other syntheses have since been reported including synthetic pathways for the preparation of optically active material and isotopically labeled material . DL-Selenomethionine has a solubility in water at 30° and pH 7 of 0.108 M which is considerably less than that for L-methionine (0.386 M). After seven hours of hydrolysis under anaerobic conditions in 6 N HCl at 110 °C selenomethionine is completely decomposed (under the same conditions 96% of methionine remains). Chemically, selenomethionine appears to be more reactive than methionine . For example, with cyanogen bromide, selenomethionine completely reacts in 0.1 M HCl in fifteen minutes while methionine requires twenty-four hours for the same reaction. In both cases the end product is homoserine. Although not as marked, this difference in reactivity was also confirmed in the reaction with hydrogen peroxide . 

Interestingly Se-methylselenomethionine, (CH3)2Se (CH2)2CH(NH2)COOH, has been identified as the predominant soluble selenium compound which is synthesized from selenite by species of Astragalus which lack the ability to accumulate selenium . As mentioned previously, the predominant selenium compound in the accumulators is Se-methylselenocysteine. 

Glutamine transaminase from bovine liver, one of the enzymes involved in methionine catabolism, utilizes SeMet as well as methionine (Blazon et al., 1994). However, with some enzymes, differences in the reaction rates for SeMet and Met have been observed. For example, SeMet is a better substrate than Met for the a,7-elimination by L-methionine 7-lyase of Pseudomonas putida (Esaki et al., 1979). The adenosyltransferase from rat liver reacts with L(+)-SeMet at 51% of the rate with L(+)-Met, and with the corresponding d(—) isomers at only 13 and 10% of the rate of L-Met (Pan and Tarver, 1967). The adenosyl transferase from yeast, on the other hand, is more active with SeMet than with Met (Mudd and Cantoni, 1957). This enzyme produces the 

General body proteins Diet selenoproteins Diet inorganic Se 

VVW Selenoprotein mRNAl reads the SeCys insertion sequence  

3 Routes of selenium metabolism in animals adapted from Jacques (2001), after Schrauzer (2000) Low and Berry (1996), and Daniels (1996). 

Glutathione peroxidases (GSH-Px) are enzymes catalyzing the reduction of hydrogen peroxide to water, and of lipid hydroperoxides to alcohols, with 

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Selenium. Selenium, thought to be widely distributed throughout body tissues, is present mostly as selenocysteine in selenoproteins or as selenomethionine (113,114). Animal experiments suggest that greater concentrations are in the kidney, Hver, and pancreas and lesser amounts are in the lungs, heart, spleen, skin, brain, and carcass (115). 

H NMR, 4, 1042 ionization potentials, 4, 1046 synthesis, 4, 1066 UV spectra, 4, 1044 Selenolo[2,3 -cjthiophenes H NMR, 4, 1042 synthesis, 4, 1067 UV spectra, 4, 1044 Selenolo[3,2-6]thiophenes dipole moments, 4, 1049 H NMR, 4, 1042 ionization potentials, 4, 1046 synthesis, 4, 1066 UV spectra, 4, 1044 Selenolo[3,4-6]thiophenes synthesis, 4, 1067 Selenolo[3,4-c]thiophenes addition reactions, 4, 1062 synthesis, 4, 1076 Selenomethionine applications, 4, 970 Selenophene, 3-acetamido-reactions, 4, 953 Selenophene, 2-acetyl-mercuration, 4, 946 nitration, 4, 947 Selenophene, 2-alkyl-reactions, 4, 45 synthesis, 4, 135, 967 Selenophene, 3-alkyl-synthesis, 4, 135, 967 Selenophene, 3-aryl-synthesis, 4, 963 Selenophene, 2-benzyl-reactivity, 4, 946 Selenophene, 2-benzyl-5-ethyl-reduction, 4, 950... 

Heinz GH, Hoffman DJ. 1998. Methyhnercury chloride and selenomethionine interactions on health and reproduction in mallards. Environ Toxicol Chem 17 139-145. 

Although it is toxic in large doses, selenium is an essential micronutrient in all known forms of life. It is a component of the unusual amino acids selenocys-teine and selenomethionine. In humans, selenium is a trace element nutrient. 

Membrane-integrated proteins were always hard to express in cell-based systems in sufficient quantity for structural analysis. In cell-free systems, they can be produced on a milligrams per milliliter scale, which, combined with labeling with stable isotopes, is also very amenable forNMR spectroscopy [157-161]. Possible applications of in vitro expression systems also include incorporation of selenomethionine (Se-Met) into proteins for multiwavelength anomalous diffraction phasing of protein crystal structures [162], Se-Met-containing proteins are usually toxic for cellular systems [163]. Consequently, rational design of more efficient biocatalysts is facilitated by quick access to structural information about the enzyme. 

Kigawa, T., Yamaguchi-Nunokawa, E., Kodama, K. et al. (2002) Selenomethionine incorporation into a protein by cell-free synthesis. Journal of Structural and Functional Genomics, 2 (1), 29-35. 

Before going on to describe the functions of the metals we observe that among heavier non-metals only selenium, chlorine and other halogens need any further comment. Selenium is found in some hydrogenases in even the most primitive life forms and may be it was required initially since it is a more effective catalytic centre than sulfur although much less available. (Compare tungsten with molybdenum later.) Its amino acid selenomethionine is coded in early DNA Later it is involved... 

Selenomethionine, CH3SeCH2CH2CHNH2COOH, 50 (Scheme 17) is also incorporated non-specifically in proteins of Clostridium kluyveri126 and in yeast127,128 apparently taking the place of methionine however, no specific biological incorporation of Se-methionine has been found.105... 

Adults fed diets 6 weeks before egg laying through day 7 of incubation containing either sodium selenite — at 1, 5, 10, or 25 mg Se/kg ration — or selenomethionine at 10 or 16 mg Se/kg ration... 

Selenomethionine group had altered immune function, altered serum enzyme activities, and elevated concentrations of selenium in liver (4 times control values) and breast muscle (14 times). Sodium selenite-treated birds had normal immune function and selenium tissue burdens however, serum enzyme activity was disrupted in the 3.5 mg/L group Adults normal. Impaired reproduction (reduced survival of ducklings, increased developmental abnormalities) for selenomethionine occurs between 4 and 8 mg/kg ration selenocysteine did not impair reproduction at 16 mg Se/kg ration... 

Ducklings fed diets containing 0, 10, 20, 40, or 80 mg Se/kg ration as selenomethionine or sodium selenite from hatching to age 6 weeks... 

Adults males given a choice between a control diet or diets with 5, 10, or 20 mg Se/kg ration as selenomethionine Adult males were fed diets supplemented with 0, 10, 20, 40, or 80 mg Se/kg ration as selenomethionine for 16-week exposure that began in November. Survivors were fed untreated diets for 4 more weeks... 

Mallards fed diet containing 0 or 15 mg Se/kg ration as seleno-DL-methionine for 21 weeks, untreated food for 12 weeks, followed by 100 mg Se/kg ration for 5 weeks for both groups Adults fed diet containing 10 mg Se/kg ration as selenomethionine for 6 weeks followed by 6 weeks on untreated diet... 

Fed diet with 15 mg Se/kg ration as selenomethionine for 21 weeks during winter, ending with onset of reproductive season Ducklings fed diets for 4 weeks containing 15 or 60 mg Se/kg ration as selenomethionine, with and without 1000 mg boron/kg ration Females that had just initiated egg laying were fed diet containing 20 mg Se/kg ration as selenomethionine for 20 days, then an untreated diet for 20 days... 

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