Selenoamino acids

Metabolism of Other Amino Acids /3-Alanine metabolism Taurine and hypotaurine metabolism Aminophosphonate metabolism Selenoamino acid metabolism Cyanoamino acid metabolism D-Glutamine and D-glutamate metabolism... 

Cavallie, S. and Cardellichio, N. (1995) Direct determination of selenoamino acids in biological tissues by anion-exchange separation and electrochemical detection. J. Chromatogr. A, 706, 429-436. 

Gilon, N., Astruc, A., Astruc, M. and Potin-Gautier, M. (1995) Selenoamino acid speciation using HPLC-ETAAS following an enzymic hydrolysis of selenoprotein. Appl. Otganomet. Chem., 9, 623-628. 

ITP was also used to concentrate selenoamino acids (methionine, ethionine, cysteine) prior to CE separation. The transfer of the analytes was carried out at a bifurcation junction as shown in Figure 6.22. As shown by the two colored dyes in Figure 6.22a, the FTP zones reached the junction. Then the zones moved pass the junction to the right CE channel (Figure 6.22b), and continued to separate further as they moved downstream (Figure 6.22c) [637]. 

Bird, S.M., Ge, H., Uden, P.C., Tyson, J.F., Block, E., and Donoyer, E. 1997a High performance liquid chromatography of selenoamino acids and organo selenium compounds. Speciation by inductively coupled plasma mass spectrometry. J. Chromatogr. 789, 349-359. 

Larsen, E.H., Hansen, M., Fan, T., and Vahl, M. 2001. Speciation of selenoamino acids, selenonium ions and inorganic selenium ion by exchange HPLC with mass spectrometric detection and its application to yeast and algae. J. Anal. At. Spectrom. 16(12), 1403-1408. 

Olson, O.E. and Palmer, I.S. 1976. Selenoamino acids in tissues of rats administered inorganic selenium. Metabolism 25, 299. 

Shimazu, F. and Tappel, A.L. 1964. Selenoamino acids decrease radiation damage to amino acids and proteins. Science 143, 369-371. 

Zdansky, G. 1968. Studies in the synthesis of selenoamino acids. Acta Univ. Upsalensis 123. 

A method was described for the selective determination of selenomethionine in wheat samples [27], where pretreatment of selenomethionine with TMAH did not induce degradation of the selenoamino acid. The procedure constitutes a suitable sample pretreatment for the selective determination of selenomethionine. Of the four detection techniques (FPD, MIP-AES, AAS, MS) compared, only MS provided LoDs sufficiently good for the determination of selenomethionine in real samples. 

Selenium is an essential element for humans and is a constituent of selenoamino acids contained in selenoenzymes, such as glutathione peroxidases. This group of enzymes catalyzes the reduction of peroxides and thereby takes part in the anti-oxidative defense of the body. A severely low Se intake may cause heart disease (Keshan s disease). Therefore, possible adverse health effects are associated with a low intake of this element and justify the focus on the low percentile Se intake in the population. The food groups that contribute the most to the Se intake are meat (including offal) followed by bread and cereals, and fish, as shown in Figure 9.8. 

Since selenoamino acids are water-soluble, leaching with hot water has been judged sufficient to recover Se species not incorporated into larger molecules. The sample is homogenized with water, sonicated or heated, and ultracentrifuged. The typical recovery of Se extracted in this way from selected yeast samples is usually ca. 10D20 percent [20, 21], Free selenoamino acids can also be separated by ultraMtration (breast milk) [22]. 

B. Michalke, Capillary electrophoresis methods for a clear identihcation of selenoamino-acids in complex matrices like human milk, Fresenius J. Anal. Chem., 351 (1995), 670D677. 

S. M. Bird, P. C. Uden, J. F. Tyson, E. Block, E. Denoyer, Speciation of selenoamino-acids and organoselenium compounds in selenium-enriched yeast using high-performance liquid chromatography Dinductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 12 (1997), 785D788. 

B. Michalke, P. Schramel, CE-methods for a clear identification of selenoamino acids in complex matrices such as human milks, J. Chromatogr. A, 716 (1995), 323-329. 

The use of methanol and ethanol, two solvents that can be well mixed with water, should be discussed separately, as they are used for several types of sample preparation on the basis of similar expected effects, but for different purposes. The feature common to both solvents is the observation that most of the sample proteins precipitate when the concentration of these compounds exceeds ca. 40 percent (v/v), thus enabling the analyst to separate the protein fraction by centrifugation or microfiltration. This way, either the proteins not intended for further analysis (e.g., enzymes or proteins that were inadequately hydrolyzed) can be removed [62], or, the purification of Se-containing proteins by successive solvent extractions can be achieved [12]. At concentrations of less than 40 percent (v/v), both methanol and ethanol are usually mixed with 0.1 moll-1 HC1 however, the use of these mixtures entails a relatively low extraction efficiency of Se (10-14 percent). Therefore, they are intended only for the extraction of water-soluble Se species, generally free selenoamino acids [15, 21, 63, 64]. 

In recent years several applications of the HC1 proteolysis have been published in the field of Se speciation, for example, as regards Se-enriched lactic acid bacteria [66], mullet and cockles [8], and algae [67], where the technique provided extraction efficiencies of greater than 90 percent and preserved the integrity of the selenoamino acids. The general usefulness of this method of Se speciation is, however, questionable. Sometimes the authors do not state clearly whether phenol - an essential compound for the prevention of oxidation of SeCys - was used or not. In practice, neither phenol nor the short-duration MW-assisted irradiation can prevent the alteration of selenoamino acids [68-71], At the moment, no final conclusion on the applicability of HC1 proteolysis can be drawn, as CRMs certified for SeCys are still unavailable. On the other hand, an Se extraction efficiency of 80-90 percent can be achieved with this method only if either proteins are at least partly separated from the other components of the matrix, for example, separate analysis of fish muscles is carried out [8], or a considerable portion of Se is originally contained in inorganic forms in the sample, as observed by B Hymer and Caruso [1] in the case of Se-enriched food supplements. 

Crews et al. [81] studied cooked cod by means of a two-step in vitro gastrointestinal enzymolysis. For the first step of sample preparation they employed gastric juice (1 percent m/v pepsin, pH = 2.0, in 0.15 mol l-1 NaCl) at 37°C for 4 h. Afterwards a pancreatin-based mixture was added to the sample solution containing 1.5 percent m/v pancreatin, 0.5 percent m/v amylase, and 0.15 percent m/v bile salts in 0.15 mol l-1 NaCl at pH = 6.9 for a further 4 h at 37°C. The relatively short (8 h) enzymatic activity and the lack of enzymes capable of hydrolyzing proteins directly into amino acids resulted in the identification of inorganic Se (IV) only, as no selenoamino acids could be detected. 

C. A. Ponce de Leon, K. L. Sutton, J. A. Caruso, P. C. Uden, Chiral speciation of selenoamino acids and selenium enriched samples using HPLC coupled to ICP-MS, J. Anal. Atom. Spectrom, 15 (2000), 1103-1107. 

J. Zheng, Y. Shibata, N. Furuta, Determination of selenoamino acids using two-dimensional ion-pair reversed phase chromatography with on-line detection by inductively coupled plasma mass spectrometry, Talanta, 59 (2003), 27-36. 

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