Seleno-L-cysteine

Because the seleno-l-cysteine (SeCys or Sec) insertion into selenoproteins occurs by a specific translational control process, it is quite difficult to express the SeCys-containing polypeptides even by the state-of-the-art genetic engineering techniques. In this paper, we describe a convenient synthetic method for the selective introduction of a SeCys derivative to polypeptides under physiological conditions. One SeCys residue in the seleno-l-cystine (SeCys-Se-Se-SeCys) methyl ester was first substituted with the Boc-protected penicillamine (Pen) methyl ester to form selenenylsulfide (SeCys-Se-S-Pen), an intermediate in the cellular glutathione peroxidase (GPx) catalytic cycle. Subsequently, the SeCys-Pen was coupled with the thiol-specific N-carboxymethylmaleimide through the α-amino group of the SeCys {[2-(N-maleimidyl)-1-oxo-ethyl-SeCys-methyl-Se-yl]-S-Pen methyl ester, MOE-SeCys-Pen}. The use of the MOE-SeCys-Pen allowed the selective introduction of the SeCys moiety to human serum albumin by alkylation of the thiol at its cysteine34, which generated the GPx-like activity responsible for the selenium atom in the MOE-SeCys-Pen.

Selenium is an essential trace element in mammals, with the majority specifically encoded as seleno-L-cysteine into a range of selenoproteins. Many of these proteins play a key role in modulating oxidative stress, via either direct detoxification of biological oxidants, or repair of oxidised residues. Both selenium- and sulphur-containing residues react readily with the wide range of oxidants (including hydrogen peroxide, radicals, singlet oxygen and hypochlorous, hypobromous, hypothiocyanous and peroxynitrous acids) that are produced during inflammation and have been implicated in the development of a range of inflammatory diseases. Whilst selenium has similar properties to sulphur, it typically exhibits greater reactivity with most oxidants, and there are considerable differences in the subsequent reactivity and ease of repair of the oxidised species that are formed. This review discusses the chemistry of low-molecular-mass organoselenium compounds (e.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for selenium speciation in dietary supplements. Chromatographic separation was performed on a TSK-Gel ODS-100V column using a mixture of 5mM ammonium acetate water solution and methanol as a mobile phase. Conditions chosen for this process allowed to separate all investigated chemical compounds of selenium: seleno-l-methionine, methyl-seleno-l-cysteine, l-selenocystine, methaneseleninic acid, selenite and selenate. A tandem mass spectrometer with an ion trap operating in negative or positive ion mode according to the selenium form being determined was used as a detector. Three extraction procedures: water extraction, enzymatic hydrolysis and sequential extraction were used for preparation of samples for the determination of the actual forms of selenium in diet supplements. The developed method was used for analysis of six dietary supplements containing selenium bought in a pharmacy and supermarket.

Selenium occurs both in prokaryocytes and eukaryocytes as a component of selenoenzymes or selenoproteins. Approximately 80 % of selenium in animal or human body occurs in the form of seleno-L-cysteine, an amino acid encoded by one of standard termination codons. Selenium is an integral component of the active site of glutathione peroxidases which plays an important role in the antioxidant system. Iodothyronine 5-deiodinase, type I is also a selenoenzyme consisting of two identical subunits which catalyzes a reductive monodeiodination of iodothyronine residues of the phenolic ring. General characteristics of several selenoproteins and selenium binding proteins are summarized, also certain facts on the effects of selenium deficiency in man and its distribution and toxicity in higher organisms, are reviewed. Selenium status in the population from selected regions in Slovakia is reported and compared with that in other countries.