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Mammalian thioredoxin reductases.
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75Se-selenomethionine uptake by the fetus.
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The surgery of primary hyperparathyroidism.
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Synthesis and secretion of selenoprotein P by cultured rat astrocytes.
Selenoprotein P is an extracellular protein that has been postulated to have an oxidant defense function. It has survival-promoting properties for cultured neurons and its mRNA is present in the brain. This study sought to determine the primary structure of rat brain selenoprotein P and to assess its production by cultured brain cells. The cDNA of selenoprotein P was isolated from a rat brain cDNA library and was found to encode the same peptide sequence as rat liver cDNA. Thus the primary structure of brain selenoprotein P is the same as selenoprotein P from liver. Astrocytes and a cerebellar granule cell preparation (CGC) were obtained from rat brains and established in culture. The CGC was estimated to contain up to 5% glial cells. Both preparations were shown to contain selenoprotein P mRNA. During incubation with (75)Se-labeled selenite, both cell preparations secreted a (75)Se-labeled protein into the medium that corresponded in size to selenoprotein P. Also, the (75)Se-labeled protein could be precipitated from both media with an antiserum to selenoprotein P. This shows that astrocytes and the CGC secrete selenoprotein P. Selenoprotein P is made in the brain and may have an oxidant defense function there.
Determination of 75Se-labelled selenite and metabolites in plasma and urine by high-performance liquid chromatography with on-line radioactivity detection.
A reversed-phase ion-pair high-performance liquid chromatographic method with on-line radioactivity detection for the simultaneous determination of 75Se-labelled selenite and metabolites has been developed. With this system a good resolution of various radiolabelled selenium complexes can be achieved. The detection limit of the radioactivity detector (signal-to-noise ratio = 3) is 49 pg of selenium (specific activity of 3 GBq/mg selenium) per millilitre of urine or plasma ultrafiltrate. The detector response is independent of both the chemical structure of the selenium complexes and the matrix composition of the samples. This method may serve as a reference system for other high-performance liquid chromatographic systems with less specific and sensitive detectors.
Selenoprotein expression in endothelial cells from different human vasculature and species.
Selenium (Se) can protect endothelial cells (EC) from oxidative damage by altering the expression of selenoproteins with antioxidant function such as cytoplasmic glutathione peroxidase (cyGPX), phospholipid hydroperoxide glutathione peroxidase (PHGPX) and thioredoxin reductase (TR). If the role of Se on EC function is to be studied, it is essential that a model system be chosen which reflects selenoprotein expression in human EC derived from vessels prone to developing atheroma. We have used [75Se]-selenite labelling and selenoenzyme measurements to compare the selenoproteins expressed by cultures of EC isolated from different human vasculature with EC bovine and porcine aorta. Only small differences were observed in selenoprotein expression and activity in EC originating from human coronary artery, human umbilical vein (HUVEC), human umbilical artery and the human EC line EAhy926. The selenoprotein profile in HUVEC was consistent over eight passages and HUVEC isolated from four cords also showed little variability. In contrast, EC isolated from pig and bovine aorta showed marked differences in selenoprotein expression when compared to human cells. This study firmly establishes the suitability and consistency of using HUVEC (and possibly the human cell line EAhy926) as a model to study the effects of Se on EC function in relation to atheroma development in the coronary artery. Bovine or porcine EC appear to be an inappropriate model.
Detection of small selenium-containing proteins in tissues of the rat.
The important role of selenium in the mammalian organism has been manifested by the detection of several selenoenzymes, and there are still numerous selenium-containing proteins to be identified. After in vivo labeling of rats with [75Se]-selenite, gel electrophoretic separation of the proteins in tissue homogenates and autoradiography of the labeled bands, information on the selenium-containing proteins present in the different tissues was obtained. In the separation by SDS-PAGE and two-dimensional IEF/SDS-PAGE a large number of selenium-containing proteins or protein subunits with apparent molecular masses in the range from 116 to 8 kDa could be distinguished. This range was extended by applying a modified Tricine-SDS-PAGE, which allows the determination of smaller proteins. Using this method in the separation of the homogenates of the adrenal, brain, diaphragm, epididymis, heart, kidney, liver, lung, pituitary, prostate, skeletal muscle, spleen, thymus and thyroid, four additional selenium-containing proteins with molecular masses of approximately 7 kDa, 5kDa, 4 kDa and 3kDa were detected. The 5 kDa protein and the 7 kDa protein were identified as selenocysteine-containing selenoproteins.
Distribution of an 18 kDa-selenoprotein in several tissues of the rat.
By combining methods for trace element analysis, tracer techniques and various biochemical and electrophoretical procedures, information on the characteristics of an 18 kDa-selenoprotein was obtained. By labeling of rats in vivo with [75Se]-selenite and gel electrophoretic separation of the proteins in tissues and subcellular fractions, a larger number of selenium-containing proteins could be distinguished. In most of the tissues investigated a labeled 18 kDa-band was present. After co-electrophoresis of the 18 kDa-bands from kidney, liver and brain we found that they all migrated in the same way. Using ultracentrifugational fractionation the 18 kDa-band was localized in the mitochondrial and microsomal membranes. Two-dimensional electrophoresis showed that it consists of a single selenium-containing protein with an isoelectric point of about 4.9-5.0. By means of proteolytic cleavage of the 18 kDa-protein and separation of its peptides by tricine-SDS-PAGE six selenium-containing peptides with molecular masses of 17, 16, 14, 12, 10, and 8 kDa were detected. After electrophoretic separation of the mitochondrial and/or microsomal proteins and acid hydrolysis of the electroeluted protein its amino acid composition was analyzed by RP-HPLC. In this way it was shown that selenium is present in the 18 kDa-protein in form of selenocysteine which is a characteristic of a genetically encoded selenoprotein.
The natBr(p,x) (73,75)Se nuclear processes: a convenient route for the production of radioselenium tracers relevant to amino acid labelling.
A possible route for the production of no-carrier-added (n.c.a.) 73Se (T(1/2) = 7.1 h) and 75Se (120 d) is introduced. D,L-2-Amino-4-([73Se]methyl-seleno) butanoic acid (D,L-[73Se]selenomethionine) with an overall radiochemical yield of > 40% could be prepared via a 3-step polymer-supported synthesis after successful separation of 73Se from KBr targets. Excitation functions for the natBr(p,x) (72,73,75)Se processes were measured from threshold up to 100 MeV utilizing pellets of pressed KBr. Targets were irradiated at the NAC cyclotron with proton beams having primary energies of 40.4, 66.8 and 100.9 MeV. The calculated 73Se yield (EOB) for 1 h irradiation in 1 microA of beam at the optimum proton energy range of 62-->42 MeV is 81.4 MBq (2.2 mCi), and the calculated 75Se yield (EOB) for the overall range 62 MeV-->threshold for the same irradiation conditions is 0.97 MBq (0.026 mCi).
Use of 75Se tracer and autoradiographic techniques in the study of schistosomiasis.
The paper provides an overview of recent studies on the use of 75Se to tag larval schistosomes and to monitor their migration and distribution patterns in naive mice and those previously exposed to cercariae. The principles and techniques of radioassay and autoradiography in studying various aspects of 75Se-labelled larval schistosomes are described. The main shortcoming of radioassay in monitoring location and movement of labelled schistosomula is that some of the label dissociates from the schistosomula and accumulates in host tissues, notably the liver. Dissociated label is indistinguishable from schistosomula-bound label making monitoring of parasite migration extremely difficult. This difficulty is overcome by compressed tissue autoradiography where labelled schistosomula can be seen as reduced silver foci on an autoradiographic film, whereas dissociated label is too diffusely distributed to produce such reduced silver foci. Furthermore, using autoradiography, quantitative information on parasite migration in normal and immunized laboratory animals can be obtained that would be impossible using traditional recovery techniques. In addition to using 75Se tracer in migration studies, the radio-isotope has potential for elucidating various aspects of schistosome transmission ecology and snail population dynamics in natural waters.
The kinetics of 75[Se]-selenite uptake by Saccharomyces cerevisiae and the vacuolization response to high concentrations.
Uptake of 75[Se]-selenite by Saccharomyces cerevisiae has been characterized. At a 0.5 mM selenite, approximately 0.14 nmol Se (10(6) cells)-1 was rapidly accumulated by the cells at a rate of approximately 56 pmol x min-1 (10(6) cells)-1 which was independent of temperature and glucose. This rapid phase was followed by a slower uptake phase which was sensitive to glucose, temperature and metabolic inhibitors [2,4-dinitrophenol (DNP), carbonyl cyanide m-chlorophenyl hydrazone (CCCP), potassium cyanide (KCN) and sodium azide (NaN3)] and therefore presumed to be metabolism-dependent. Two transport systems appeared to be involved in selenite uptake. At the low range of selenite concentrations used (0.025-0.1 mM), a high affinity transport system occurred with apparent Km and Vmax values of 54.0 microM and 3.14 pmol x min(-1) (10(6) cells)(-1) respectively. A low affinity system was present at higher concentrations (0.1-1.0 mM) with apparent kinetic parameters of Km = 435 microM and Vmax = 11.6 pmol x min(-1) (10(6) cells)(-1). Elevated sulphate concentrations (up to 2.5 mM) did not affect the accumulation of selenite. However, the transport rate from 0.5 mM selenite was stimulated by sulphite, with the maximum effect occurring at 0.5 mM sulphite. Methionine had a detectable inhibitory action on selenite uptake whereas cystine and cysteine completely inhibited active transport of selenite. Transmission electron microscopy of 5 mM selenite-grown cells revealed the presence of abundant small cytoplasmic vesicles containing electron-dense granules which could represent an intracellular selenium-detoxification mechanism.
Identification and synthesis of a naturally occurring selenonucleoside in bacterial tRNAs: 5-[(methylamino)methyl]-2-selenouridine.
Escherichia coli, Clostridium sticklandii, and Methanococcus vannielii synthesize 75Se-labeled amino acid transfer ribonucleic acids [( 75Se]tRNAs) when grown with low levels (approximately equal to 1 microM) of 75SeO32-. When E. coli [75Se]tRNA was digested to nucleosides and analyzed by reversed-phase high-performance liquid chromatography, a single selenonucleoside accounted for 70-90% of the 75Se label in the bulk tRNA. This nucleoside was shown to be indistinguishable in a number of its properties from authentic 5-[(methylamino)methyl]-2-selenouridine. Preparation of the authentic selenonucleoside was accomplished and the synthetic compound characterized by its UV and 1H NMR spectral properties. The new selenonucleoside also accounted for 40-60% of the 75Se found in [75Se]tRNA from C. sticklandii or M. vannielii. Each of these anaerobic bacteria contains one additional selenonucleoside in their tRNA populations distinct from 5-[(methylamino)methyl]-2-selenouridine. Pure seleno-tRNAGlu isolated from C. sticklandii contains one 5-[(methylamino)methyl]-2-selenouridine and one 4-thiouridine per tRNA molecule.
Reduction of the selenotrisulfide derivative of glutathione to a persulfide analog by glutathione reductase.
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Biosynthesis of dimethylarsine by Methanobacterium.
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Are selenocystine and selenomethionine synthesized in vivo from sodium selenite in mammals?
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Synthesis, purification, and structural characterization of the dimethyldiselenoarsinate anion.
A novel arsenic-selenium solution species was synthesized by reacting equimolar sodium selenite and sodium dimethylarsinate with 10 mol equiv of glutathione (pH 7.5) in aqueous solution. The solution species showed a single (77)Se NMR resonance at 112.8 ppm. Size-exclusion chromatography (SEC) using an inductively coupled plasma atomic emission spectrometer (ICP-AES) as the simultaneous arsenic-, selenium-, sulfur-, and carbon-specific detector revealed an arsenic-selenium moiety with an As:Se molar ratio of 1:2. Electrospray ionization mass spectrometry (ESI-MS) of the chromatographically purified compound showed a molecular mass peak at m/z 263 in the negative ion mode. Fragmentation of the parent ion (ESI-MS-MS) produced (CH(3))(2)As(-) and Se(2)(-) fragments. Arsenic and selenium extended X-ray absorption fine structure spectroscopy (EXAFS) of the purified species revealed two As-C interactions at 1.943 A and two As-Se interactions at 2.279 A. On the basis of these results this novel solution species is identified as the dimethyldiselenoarsinate anion.
Synthesis of seleno-toluidine blue.
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