Incorporation Of Selenium Research Articles

Incorporation of selenium into carbon films by chemical vapor deposition

The introduction of selenium into carbon thin films was tried by a chemical vapor deposition (CVD) from selenium and acrylic acid vapors at 900 °C on different substrates. No conclusive evidence of intercalation of selenium into the carbon films was obtained, but the materials contained a small quantity of selenium. Electrical conductivity of the film deposited on a silicon wafer was four times higher than that on a quartz glass.

Removal of Selenocyanate in Water by Precipitation: Characterization of Copper−Selenium Precipitate by X-ray Diffraction, Infrared, and X-ray Absorption Spectroscopy

During refining of sour crude oils produced from reservoirs containing seleniferous marine shales, selenium is concentrated into process waters and wastewaters. Selenium, present in the waters as selenocyanate, must be removed to meet regulatory discharge limits. Treatment of wastewaters with copper(II) salts effectively precipitates selenium. An objective of the present study was to determine whether selenium was precipitated as elemental Se or immobilized in the form of cyanate complexes or any other form that remains to be identified. The precipitate had a Se/(Se+S) mole ratio of 0.09. The incorporation of selenium in the copper thiocyanate lattice was proven by X-ray diffraction. The presence of native selenium was disallowed by Se K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Selenium was shown by EXAFS to be present as selenide and surrounded by one nearest C atom and three next-nearest Cu atoms. This local environment is typic...

Selenium‐Dependent Glutathione Peroxidase and other Selenoproteins: Their Synthesis and Biochemical Roles

Selenium-dependent glutathione peroxidase (SeGPX, EC 1.11.1.9) acts as part of the antioxidant defence of the body. It functions as a highly efficient catalyst to reduce a wide variety of intracellular peroxides, including hydrogen and lipid peroxides, thereby detoxifying these potentially damaging molecules. Thus selenium has a critical role in normal cellular biochemistry and the proposal has been made that deficiency of selenium in the diet can lead to a number of clinical disorders. World-wide interest in selenoproteins is now evident. In general, the active site of SeGPX and of other selenoproteins is based upon a selenium moiety (generally a single covalently bound atom of selenium) present as the amino acid selenocysteine. There has been an extension of the genetic code to include the codon TGA (in the correct DNA context) as the 21st codon specifying the presence of selenocysteine in the polypeptide structure of selenoproteins. Recent discoveries in SeGPX biochemistry and molecular biology in relation to its protective function are reviewed here in comparison to other selenoproteins. The mechanisms of selenium incorporation into selenoproteins is also described. In the future, antioxidant enzymes such as selenium-dependent glutathione peroxidase may find a use in biotechnology for the protection of enzymes and cellular membranes. While it is recognised that in cost terms the use of enzyme mimics of SeGPX may be more advantageous, large-scale in-vitro production of the selenoproteins is now possible and their value can be readily assessed. © 1997 SCI.

Selenium-Dependent Glutathione Peroxidase and other Selenoproteins: Their Synthesis and Biochemical Roles

Selenium-dependent glutathione peroxidase (SeGPX, EC 1.11.1.9) acts as part of the antioxidant defence of the body. It functions as a highly efficient catalyst to reduce a wide variety of intracellular peroxides, including hydrogen and lipid peroxides, thereby detoxifying these potentially damaging molecules. Thus selenium has a critical role in normal cellular biochemistry and the proposal has been made that deficiency of selenium in the diet can lead to a number of clinical disorders. World-wide interest in selenoproteins is now evident. In general, the active site of SeGPX and of other selenoproteins is based upon a selenium moiety (generally a single covalently bound atom of selenium) present as the amino acid selenocysteine. There has been an extension of the genetic code to include the codon TGA (in the correct DNA context) as the 21st codon specifying the presence of selenocysteine in the polypeptide structure of selenoproteins. Recent discoveries in SeGPX biochemistry and molecular biology in relation to its protective function are reviewed here in comparison to other selenoproteins. The mechanisms of selenium incorporation into selenoproteins is also described. In the future, antioxidant enzymes such as selenium-dependent glutathione peroxidase may find a use in biotechnology for the protection of enzymes and cellular membranes. While it is recognised that in cost terms the use of enzyme mimics of SeGPX may be more advantageous, large-scale in-vitro production of the selenoproteins is now possible and their value can be readily assessed. © 1997 SCI.

Selenium and Fertility in Animals and Man–A Review

To evaluate the information on selenium with relation to fertility in animals and man the available literature was reviewed. Selenium is incorporated in the sperm mitochondria capsule and may thus affect the behavior and function of the spermazoon. Se seems to be essential for normal spermatozoa development in both experimental animals and in livestock and probably also in humans. Regarding selenium and female fertility only sparse information exists. In experimental animals a low selenium level affects fertility in males, but little attention has been devoted to female reproductive performance, and the data are insufficient for conclusion. In livestock numerous investigations have been performed and the effects of selenium supplementation often in combination with other antioxidants have been evaluated, but no valid conclusion can be drawn. In general adequate nutritional supply will secure optimal reproduction in both males and females, while additional supplementation seems to have a negative effect. In humans contradictive information is found. Both low and high sperm selenium concentrations are reported to have a negative influence on the number of spermatozoa and on the motility. The optimal sperm selenium concentration waits to be defined. Some evidence indicates that a metabolic defect in a selenium incorporation into sperm cells may be associated with human infertility. No human data relating selenium to female infertility were found.

Interactions between dietary selenium, copper and sodium nitroprusside, a source of cyanide in growing chicks and laying hens

1. Diets containing supplements of selenium (10 mg/kg as sodium selenite), copper (500 mg/kg as copper (II) sulphate) and sodium nitroprusside (SNP 300 mg/kg) as a source of cyanide, were fed singly and in all possible combinations to chicks from 14 to 35 d of age. 2. Both copper and SNP individually alleviated the growth depression caused by excess selenium but interacted adversely with one another. The effect of SNP was to decrease liver selenium but copper increased it. Despite this contrast it is suggested that both achieve their beneficial effects through influences on the fraction of liver selenium that can be reduced to volatile forms by hydrochloric acid and zinc. 3. In a second experiment the effects of diets containing additional selenium (2 mg/kg as sodium selenite or selenomethionine) with or without additional copper (100 mg/kg) or SNP (100 mg/kg) on selenium incorporation into eggs were compared. 4. SNP reduced incorporation from selenite whereas copper had no effect. However, copper reduced the incorporation from selenomethionine into protein fractions of egg white as much as SNP.

Decreased glutathione peroxidase activity in mice in response to nafenopin is caused by changes in selenium metabolism

The activity of selenium-dependent glutathione peroxidase is known to be reduced in the liver of both rats and mice after exposure to nafenopin, as well as other peroxisome proliferators. The mechanism for this down-regulation is not known, but might involve changes in incorporation of selenium into selenoproteins. In this paper we show that both incorporation of selenium into selenoproteins and the level of selenium in liver is reduced in mice treated with nafenopin. The activity of selenium dependent glutathione peroxidase (GPx), as well as incorporation of selenium into its 23 kD subunit were found to be decreased. Contrary to what might have been expected, the decreased GPx activity was detected concomitantly with a slight increase in mRNA levels after 10 days of treatment, while a small decrease in mRNA levels was detected in treated animals after 26 weeks, together with the decrease in GPx-activity. Incorporation of selenium into liver fatty acid binding protein (L-FABP) was also decreased, even though large increases in protein and mRNA levels were detected. Taken together these data suggest that the decrease in GPx-activity in response to nafenopin is due to post-transcriptional mechanisms, involving changes in selenium metabolism.

Use of stable isotopic selenium as a tracer to follow incorporation of selenium into selenoproteins.

Stable isotopes of selenium (Se) have been used in human studies to measure Se absorption, retention and excretion. The purpose of this study was to examine whether stable Se could also be used to follow the incorporation of Se into selenoproteins and whether selenoproteins are labeled with stable isotopes the same way they are with radioactive Se. Rats fed either a Se-deficient or a high-Se diet were injected with either a radioactive (75Se) or a stable isotope of Se (77Se), and the liver cytosol was chromatographed on Sephadex G-200. Compared with 75Se, a greater percentage of 77Se was incorporated into cytosol, but the distribution and the effect of dietary Se was similar for both isotopes. New Zealand long-eared rabbits were also injected with either 77Se or 75Se, and the plasma was chromatographed. More of the 75Se was incorporated into the plasma, but again the patterns of incorporation were similar for both isotopes. Plasma from a male subject who ingested 60 micrograms of 77Se was chromatographed, and the stable Se was detected in column fractions and showed a distribution similar to that observed for rabbit plasma. Finally, a polyacrylamide gel electrophoresis (PAGE) method was developed that allowed loading of sufficient protein to analyze for 77Se in individual protein fractions. The distribution of 77Se and 75Se in rabbit plasma was similar. Human plasma was electrophoresed by a similar method and peaks of 56 and 23 kDa were detected. These data show that stable isotopes of Se can be used for selenoprotein production in the same way as radioactive isotopes. They also show that, when physiological amounts of stable Se are ingested by humans, the isotope can be detected in blood-borne proteins separated by column chromatography and PAGE.

Cloning and Functional Characterization of Human Selenophosphate Synthetase, an Essential Component of Selenoprotein Synthesis

Selenocysteine is co-translationally incorporated into prokaryotic and eukaryotic selenoproteins at in-frame UGA codons. However, the only component of the eukaryotic selenocysteine incorporation machinery identified to date is the selenocysteine-specific tRNA(Sec). In prokaryotes, selenocysteine is synthesized from seryl-tRNA(Sec) and the active selenium donor, selenophosphate. Selenophosphate is synthesized from selenide and ATP by the selD gene product, selenophosphate synthetase, and is required for selenocysteine synthesis and incorporation into bacterial selenoproteins. We have now cloned human selD and shown that transfection of the human selD cDNA into mammalian cells results in increased selenium labeling of a mammalian selenoprotein, type 1 iodothyronine deiodinase. Despite significant differences between the mechanisms of selenoprotein synthesis in prokaryotes and eukaryotes, human selD weakly complements a bacterial selD mutation, partially restoring selenium incorporation into bacterial selenoproteins. Human selenophosphate synthetase has only 32% homology with the bacterial protein, although a highly homologous region that has similarity to a consensus ATP/GTP binding domain has been identified. Point mutations within this region result in decreased incorporation of selenium into type 1 iodothyronine deiodinase in all but one case. Further analysis revealed that reduced selenium labeling was due to altered ATP binding properties of the mutant selenophosphate synthetases.

Crystallization and Preliminary X-ray Diffraction Characterisation of Both a Native and Selenomethionyl VLA-4 Binding Fragment of VCAM-1

Soluble fragments of the extracellular region of vascular cell adhesion molecule 1 (VCAM-1) expressed in Escherichia coli retain functional adhesive activity. An integrin (VLA-4) binding fragment consisting of the N-terminal two immunoglobulin-like domains (VCAM-d1,2) has been crystallized. The crystals belong to space group P 2 12 12 1 with cell dimensions of a = 52.7 Å, b = 66.5 Å, c = 113.2 Å and contain two molecules in the crystallographic asymmetric unit. A batch of protein produced in the standard E. coli strain (HW1110), but grown in the presence of selenomethionine enriched media, showed 85% incorporation of selenium in place of sulphur at methionine residues. The selenomethionyl VCAM-d1,2 was crystallized by microseeding techniques initially using the native crystals for nucleation. Both native and selenomethionyl crystals diffract X-rays to a minimum Bragg spacing of 1.8 Å

Study of the selenium incorporation in sputtered Cu, in alloys

Abstract Thin CuInSe 2 films have been prepared in a two stage process by sputtering on Mo/glass substrates alternate Cu, In layers followed by selenization by vacuum evaporation. The compostional and the structural analysis of the compounds has been carried out by EDS and XRD, respectively. Selenium incorporated in the ternary compound assumes a constant value around 48% (at/at) while the Cu/In ratio ranges between 0.8 and 1.2. As the copper content is further lowered, selenium decisively increases up to almost 51% when Cu/In is 0.6. The inversion point in the Se-Cu/In diagram has been correlated to the formation of a secondary phase identified as the chalcopyrite vacancy-variant compound CuIn 3 Se 5 (OVC). The results are independent on the type of metallic precursors and on their preparation conditions.

A purified selenophosphate-dependent enzyme from Salmonella typhimurium catalyzes the replacement of sulfur in 2-thiouridine residues in tRNAs with selenium.

A tRNA-modifying enzyme tentatively termed tRNA 2-selenouridine synthase was purified by a five-step procedure that resulted in 50-60% pure preparations. This enzyme catalyzes the conversion of a 5-methylaminomethyl-2-thiouridine residue in the tRNA substrate to 5-methylaminomethyl-2-selenouridine. The selenium donor substrate for this reaction is shown to be selenophosphate which is formed from ATP and selenide by selenophosphate synthetase. Replacement of sulfur with selenium in tRNAs catalyzed by tRNA 2-selenouridine synthase occurs in the absence of ATP. The dependence of reaction velocity on selenophosphate concentration obeys Michaelis-Menten kinetics indicating an apparent Km value of 17.1 microM. Bulk thio-tRNA preparations from Escherichia coli and Salmonella typhimurium are equally effective as substrates for the selenium incorporation reaction. An intact 3' end of the tRNA molecule does not seem to be essential for selenium incorporation. Identity of the product of the reaction was confirmed by HPLC analysis of digests of [75Se]seleno-tRNAs labeled by incubation with the purified enzyme. A labeled compound in the nucleoside mixture was coeluted with authentic 5-methylaminomethyl-2-selenouridine.

HPLC/ICP Mass Spectrometric Study of the Selenium Incorporation into Cyanobacterial Metallothionein Induced under Heavy-Metal Stress

Selenium is a toxic element which can cause environmental pollution. Its uptake and incorporation by Zn2+-induced metallothionein (MT) biosynthesis in a cyanobacterium were studied by means of high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometric (ICPMS) detection. When we cultured the cells in selenite-enriched media, as much as 60% of the total selenium in the water-soluble cell components was incorporated into MT, which exists as two major isoforms but occupies a very minor fraction of the overall proteins. Existence of two pathways has been shown for the first time for selenium incorporation into the cyanobacterial MT; one is the S-Se bonding which can be reductively broken by 2-mercaptoethanol, and the other is the formation of selenocysteine followed by its incorporation into the MT peptide chain. No essential difference was noted between selenite and selenate regarding the uptake or the incorporation of Se. The present HPLC/ICPMS system can elucidate biological processes of environmental chemical importance at the molecular level.

X-ray, reflection high electron energy diffraction and X-ray photoelectron spectroscopy studies of InSe and γ-In 2Se 3 thin films grown by molecular beam deposition

In x Se y thin films have been grown on amorphous substrates by molecular beam deposition of indium and selenium under ultra high vacuum. The growth conditions of InSe and γ-In 2Se 3 thin films have been investigated by X-ray diffraction, reflection high energy electron diffraction and X-ray photoelectron spectroscopy measurements. A phase diagram of In x Se y thin films has been determined as a function of substrate temperature and equivalent partial pressure ration R = P Se/ P In. A two-dimensional growth mode of InSe thin films is observed by reflection high energy electron diffraction investigations for 225 °C< T s<350 °C. The selenium incorporation is discussed as a function of substrate temperature and equivalent partial pressure ratio R.

Simultaneous impurity doping with Zn and Se in AlGaInP by MOVPE

We studied the simultaneous doping with zinc and selenium in AlGaInP by metalorganic vapor phase epitaxy. We measured the dependence of zinc and selenium incorporation on substrate orientation from (100) to (311)A faces, showing that the simultaneously doped layer becomes n-type on the (100) face and p-type on the (311)A face. The simultaneously doped layer was examined by photoluminescence, capacitance-voltage, Hall, and secondary ion mass spectrometry analysis. We showed that the simultaneously doped layers have good electrical conduction characteristics and optical qualities for cladding layers in optical devices. We also demonstrated a lateral p-n junction on a patterned substrate.

Structural and Electrical Investigations of the Anion Exchange in Polycrystalline CuIn(S, Se)2 Thin Films

The transition from the selenide to the sulfide in coevaporated CuIn(S, Se)2 thin films is investigated regarding morphology, structural properties, incorporation of sulphur versus selenium, the existence of secondary phases and electrical properties. The segregation behaviour of secondary phases in In-rich and Cu-rich films and the influence on the film growth are discussed. Measurement techniques involve SEM, XRD and acceleration voltage dependent WDS.

Solar cells based on CuIn(Se, S)2

Abstract In this contribution we report on three- and four source evaporation of CuIn(Se, S)2 thin films. The existence of secondary phases as well as texture effects are discussed for these thin films. The quaternary system CuIn(Se, S)2 will be considered regarding incorporation of selenium versus sulphur. Results of heterojunctions completed with (Zn, Cd)S or a composite window consisting of a thin CdS buffer and a highly conductive ZnO window layer will be reported and analyzed. A main feature will be the influence of CuS on the heterojunction and the methods to overcome this problem. Devices with an active area efficiency exceeding 10% could be obtained.

UV laser assisted growth of molecular beam epitaxial ZnSe

Photo-assisted molecular beam epitaxy of ZnSe on GaAs substrates with UV irradiation is reported. The growth rate is observed to be a function of the layer thickness and at high UV levels growth can be totally supressed. Photo-assisted doping has been investigated for the first time in ZnSe and changes of up to 20x in the doping level are reported for iodine, n-type doped material. The results are discussed in terms of hole accumulation at the surface affecting the incorporation of selenium and iodine.

Expression and operon structure of the sel genes of Escherichia coli and identification of a third selenium-containing formate dehydrogenase isoenzyme.

A detailed analysis of the expression of the sel genes, the products of which are necessary for the specific incorporation of selenium into macromolecules in Escherichia coli, showed that transcription was constitutive, being influenced neither by aerobiosis or anaerobiosis nor by the intracellular selenium concentration. The gene encoding the tRNA molecule which is specifically aminoacylated with selenocysteine (selC) proved to be monocistronic. In contrast, the other three sel genes (selA, -B, and -D) were shown to be constituents of two unlinked operons. The selA and selB genes formed one transcriptional unit (sel vector AB), while selD was shown to be the central gene in an operon including two other genes, the promoter distal of which (topB) encodes topoisomerase III. The promoter proximal gene (orf183) was sequenced and shown to encode a protein consisting of 183 amino acids (Mr, 20,059), the amino acid sequence of which revealed no similarity to any currently known protein. The products of the orf183 and topB genes were required neither for selenoprotein biosynthesis nor for selenation of tRNAs. selAB transcription was driven by a single, weak promoter; however, two major selD operon transcripts were identified. The longer initiated just upstream of the orf183 gene, whereas the 5' end of the other mapped in a 116-bp nontranslated region between orf183 and selD. Aerobic synthesis of all four sel gene products incited a reexamination of a weak 110-kDa selenopolypeptide which is produced under these conditions. The aerobic appearance of this 110-kDa selenopolypeptide was not a consequence of residual expression of the gene encoding the 110-kDa selenopolypeptide of the anaerobically inducible formate dehydrogenase N (FDHN) enzyme, as previously surmised, but rather resulted from the expression of a gene encoding a third, distinct selenopolypeptide in E. coli. A mutant strain no longer capable of synthesizing the 80- and 110-kDa selenopolypeptides of FDHH and FDHN, respectively, still synthesized this alternative 110-kDa selenopolypeptide which was present at equivalent levels in cells grown aerobically and anaerobically with nitrate. Furthermore, this strain exhibited a formate- and sel gene-dependent respiratory activity, indicating that it is probable that this selenopolypeptide constitutes a major component of the formate oxidase, an enzyme activity initially discovered in aerobically grown E. coli more than 30 years ago.

Effects of Chemical Form and Dosage on the Incorporation of Selenium into Tissue Proteins in Rats

We investigated the incorporation of Se into the proteins of liver and muscle, the two main Se pools, during replenishment of Se-deficient rats with normal or large doses of 75Se-labeled selenite and selenomethionine, doses equivalent to the amounts ingested from a diet with 0.2 or 2 mg Se/kg. With the higher intake, Se levels were elevated. More Se was retained from selenomethionine than from selenite. After separation of the labeled proteins, it was apparent that the higher tissue Se contents were mainly due to nonspecific incorporation into a large number of proteins. We observed no differences between the two chemical forms with regard to the formation of the specific selenoproteins. The 10-fold increase in the Se supply led to a relatively small rise in the levels of these compounds. The results indicate that after ingestion of normal amounts of selenite nearly all of the element is present in the specific selenoproteins. With increasing doses a part is also incorporated nonspecifically into numerous other proteins. In the case of selenomethionine, a part of the element follows the same metabolic pathways, but a percentage is also deposited directly and nonspecifically into proteins in place of methionine.