Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Selenium Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,423 records · Page 79Linked to original sources
PubMed1991

Effect of organic and inorganic mercury on human sperm motility.

The effects of mercuric chloride and methyl mercuric chloride on the motility of human spermatozoa in vitro were investigated. Organic as well as inorganic mercury compounds decreased the percentage of motile spermatozoa. After 15 min. incubation with 40 microM mercuric chloride a significant decrease in sperm motility was observed. Less than 5% of spermatozoa were motile after 30 min. of exposure to 20 microM methyl mercuric chloride. These effects could not be attenuated by addition of 5 microM sodium selenite. The ultrastructural localization of mercury was demonstrated by autometallography. Silver-enhanced mercury deposits could be demonstrated only in spermatozoa exposed to inorganic mercury. In these cells mercury grains were most abundant in membranes of midpiece and tail.

Antiviral Agents↗
PubMed1995

Comparison of two shampoos for treatment of Malassezia pachydermatis-associated seborrhoeic dermatitis in basset hounds.

A randomised-double-blind parallel study compared the clinical and antimicrobial efficacies of a miconazole-chlorhexidine shampoo with a selenium sulphide shampoo for the treatment of seborrhoeic dermatitis associated with Malassezia pachydermatis in 33 basset hounds. All 16 miconazole-chlorhexidine treated hounds and 11 of 17 selenium sulphide treated hounds improved when shampooed at three-day intervals for three weeks. The miconazole-chlorhexidine treated hounds showed significantly greater reductions in pruritus (P < 0.01), erythema (P < 0.001), exudation (P < 0.01) and overall severity (P < 0.001), and in counts of M pachydermatis (P < 0.001), total bacteria (P < 0.001) and coagulase-positive staphylococci (P < 0.001), when compared to the selenium sulphide treated group. Improvements in scaling and coat condition did not vary significantly between the two groups. These results indicate that seborrhoeic dermatitis in basset hounds is often associated with elevated cutaneous populations of M pachydermatis and bacteria, and that the miconazole-chlorhexidine shampoo is more effective than the selenium sulphide product for the treatment for this disease.

Animals↗
PubMed1988

Transport of selenate and sulphate across the intestinal brush-border membrane of pig jejunum by two common mechanism.

The objectives of the present study were to find out whether selenate and sulphate are transported by a common Na+-dependent transport mechanism across the intestinal brush-border membrane and whether selenate is also transported by the anion-exchange system transporting sulphate across the brush-border membrane. Results from cis-inhibition as well as from trans-stimulation experiments show that selenate and sulphate are transported across the brush-border membrane by both Na+ co-transport and anion exchange. The influence of various dicarboxylates (oxalate, oxaloacetate, glutamate) and of the anion-exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS) on selenate and sulphate transport across the brush-border membrane was also investigated. Under Na+-gradient conditions selenate uptake across the brush-border membrane was reduced by oxalate and oxaloacetate but not by L-glutamate or L-leucine. Additionally sulphate uptake under this condition was significantly inhibited by oxalate (about 50%) and DIDS (25%). Sulphate transport by anion exchange was inhibited about 80% by both oxalate and DIDS. These results suggest that under Na+-gradient conditions sulphate (selenate) uptake in part occurs via anion exchange. Furthermore, oxalate seems to inhibit both Na+-sulphate (selenate) co-transport and sulphate (selenate) transport by anion exchange.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1962

Intestinal transport of selenium-75 selenomethionine.

When measured simultaneously, selenium-75 selenomethionine accumulated identically with sulfur-35 methionine across everted hamster intestinal sacs in the presence of carrier methionine. The apparent K(m) for L-methionine transport was 0.8 x 10(-3) M, as calculated from the beta emissions of S(35)-methionine or the gamma emissions of Se(75)-selenomethionine. Absorption of Se(75)-selenomethionine from the gastrointestinal tract of man also occurred, with peak blood levels being reached in about 3 hours. Because of the 122-day half-life of selenium-75 and its multiple gamma emissions, Se(75)-selenomethionine may serve as a tool in evaluating amino-acid absorption.

Amino Acids↗
PubMed2006

Resolution of distinct membrane-bound enzymes from Enterobacter cloacae SLD1a-1 that are responsible for selective reduction of nitrate and selenate oxyanions.

Enterobacter cloacae SLD1a-1 is capable of reductive detoxification of selenate to elemental selenium under aerobic growth conditions. The initial reductive step is the two-electron reduction of selenate to selenite and is catalyzed by a molybdenum-dependent enzyme demonstrated previously to be located in the cytoplasmic membrane, with its active site facing the periplasmic compartment (C. A. Watts, H. Ridley, K. L. Condie, J. T. Leaver, D. J. Richardson, and C. S. Butler, FEMS Microbiol. Lett. 228:273-279, 2003). This study describes the purification of two distinct membrane-bound enzymes that reduce either nitrate or selenate oxyanions. The nitrate reductase is typical of the NAR-type family, with alpha and beta subunits of 140 kDa and 58 kDa, respectively. It is expressed predominantly under anaerobic conditions in the presence of nitrate, and while it readily reduces chlorate, it displays no selenate reductase activity in vitro. The selenate reductase is expressed under aerobic conditions and expressed poorly during anaerobic growth on nitrate. The enzyme is a heterotrimeric (alphabetagamma) complex with an apparent molecular mass of approximately 600 kDa. The individual subunit sizes are approximately 100 kDa (alpha), approximately 55 kDa (beta), and approximately 36 kDa (gamma), with a predicted overall subunit composition of alpha3beta3gamma3. The selenate reductase contains molybdenum, heme, and nonheme iron as prosthetic constituents. Electronic absorption spectroscopy reveals the presence of a b-type cytochrome in the active complex. The apparent Km for selenate was determined to be approximately 2 mM, with an observed Vmax of 500 nmol SeO4(2-) min(-1) mg(-1) (kcat, approximately 5.0 s(-1)). The enzyme also displays activity towards chlorate and bromate but has no nitrate reductase activity. These studies report the first purification and characterization of a membrane-bound selenate reductase.

Cell Membrane↗
PubMed1988

Selenate reduction by bacteria from a selenium-rich environment.

Samples collected from Kesterson Reservoir were screened for bacterial presence and selenate reduction capability. Selenate concentrations of 100 mg/liter were not toxic to indigenous bacteria. Of the 44 samples collected, 20 possessed microbial populations capable of reducing selenate. Reduction was observed in 4% of the water samples, 92% of the sediment samples, and 100% of the soil samples. Microbial reduction of 100 mg of selenate per liter was complete within 1 week of incubation. Up to 75 mg of selenate per liter was reduced beyond selenite to an insoluble red precipitate. Data collected indicate that indigenous bacteria have a significant role in the biogeochemical cycling of selenium.

Bacteria↗
PubMed1991

In situ bacterial selenate reduction in the agricultural drainage systems of western Nevada.

Dissimilatory in situ selenate reduction to elemental selenium in sediments from irrigated agricultural drainage regions of western Nevada was measured at ambient Se oxyanion concentrations. Selenate reduction was rapid, with turnover rate constants ranging from 0.04 to 1.8 h-1 at total Se concentrations in pore water of 13 to 455 nM. Estimates of removal rates of selenium oxyanions were 14.38, and 155 mumol m-2 day-1 for South Lead Lake, Massie Slough, and Hunter Drain, respectively.

Agriculture↗
PubMed1999

Simultaneous reduction of nitrate and selenate by cell suspensions of selenium-respiring bacteria.

Washed-cell suspensions of Sulfurospirillum barnesii reduced selenate [Se(VI)] when cells were cultured with nitrate, thiosulfate, arsenate, or fumarate as the electron acceptor. When the concentration of the electron donor was limiting, Se(VI) reduction in whole cells was approximately fourfold greater in Se(VI)-grown cells than was observed in nitrate-grown cells; correspondingly, nitrate reduction was approximately 11-fold higher in nitrate-grown cells than in Se(VI)-grown cells. However, a simultaneous reduction of nitrate and Se(VI) was observed in both cases. At nonlimiting electron donor concentrations, nitrate-grown cells suspended with equimolar nitrate and selenate achieved a complete reductive removal of nitrogen and selenium oxyanions, with the bulk of nitrate reduction preceding that of selenate reduction. Chloramphenicol did not inhibit these reductions. The Se(VI)-respiring haloalkaliphile Bacillus arsenicoselenatis gave similar results, but its Se(VI) reductase was not constitutive in nitrate-grown cells. No reduction of Se(VI) was noted for Bacillus selenitireducens, which respires selenite. The results of kinetic experiments with cell membrane preparations of S. barnesii suggest the presence of constitutive selenate and nitrate reduction, as well as an inducible, high-affinity nitrate reductase in nitrate-grown cells which also has a low affinity for selenate. The simultaneous reduction of micromolar Se(VI) in the presence of millimolar nitrate indicates that these organisms may have a functional use in bioremediating nitrate-rich, seleniferous agricultural wastewaters. Results with (75)Se-selenate tracer show that these organisms can lower ambient Se(VI) concentrations to levels in compliance with new regulations proposed for release of selenium oxyanions into the environment.

Bacillus↗
PubMed2000

Fate of selenate and selenite metabolized by Rhodobacter sphaeroides.

Cultures of a purple nonsulfur bacterium, Rhodobacter sphaeroides, amended with approximately 1 or approximately 100 ppm selenate or selenite, were grown phototrophically to stationary phase. Analyses of culture headspace, separated cells, and filtered culture supernatant were carried out using gas chromatography, X-ray absorption spectroscopy, and inductively coupled plasma spectroscopy-mass spectrometry, respectively. While selenium-amended cultures showed much higher amounts of SeO(3)(2-) bioconversion than did analogous selenate experiments (94% uptake for SeO(3)(2-) as compared to 9.6% for SeO(4)(2-)-amended cultures from 100-ppm solutions), the chemical forms of selenium in the microbial cells were not very different except at exposure to high concentrations of selenite. Volatilization accounted for only a very small portion of the accumulated selenium; most was present in organic forms and the red elemental form.

Chromatography, Gas↗
PubMed2000

Production of volatile derivatives of metal(loid)s by microflora involved in anaerobic digestion of sewage sludge.

Gases released from anaerobic wastewater treatment facilities contain considerable amounts of volatile methyl and hydride derivatives of metals and metalloids, such as arsine (AsH(3)), monomethylarsine, dimethylarsine, trimethylarsine, trimethylbismuth (TMBi), elemental mercury (Hg(0)), trimethylstibine, dimethyltellurium, and tetramethyltin. Most of these compounds could be shown to be produced by pure cultures of microorganisms which are representatives of the anaerobic sewage sludge microflora, i.e., methanogenic archaea (Methanobacterium formicicum, Methanosarcina barkeri, Methanobacterium thermoautotrophicum), sulfate-reducing bacteria (Desulfovibrio vulgaris, D. gigas), and a peptolytic bacterium (Clostridium collagenovorans). Additionally, dimethylselenium and dimethyldiselenium could be detected in the headspace of most of the pure cultures. This is the first report of the production of TMBi, stibine, monomethylstibine, and dimethylstibine by a pure culture of M. formicicum.

Anaerobiosis↗
PubMed2001

Characterization of the reduction of selenate and tellurite by nitrate reductases.

Preliminary studies showed that the periplasmic nitrate reductase (Nap) of Rhodobacter sphaeroides and the membrane-bound nitrate reductases of Escherichia coli are able to reduce selenate and tellurite in vitro with benzyl viologen as an electron donor. In the present study, we found that this is a general feature of denitrifiers. Both the periplasmic and membrane-bound nitrate reductases of Ralstonia eutropha, Paracoccus denitrificans, and Paracoccus pantotrophus can utilize potassium selenate and potassium tellurite as electron acceptors. In order to characterize these reactions, the periplasmic nitrate reductase of R. sphaeroides f. sp. denitrificans IL106 was histidine tagged and purified. The V(max) and K(m) were determined for nitrate, tellurite, and selenate. For nitrate, values of 39 micromol x min(-1) x mg(-1) and 0.12 mM were obtained for V(max) and K(m), respectively, whereas the V(max) values for tellurite and selenate were 40- and 140-fold lower, respectively. These low activities can explain the observation that depletion of the nitrate reductase in R. sphaeroides does not modify the MIC of tellurite for this organism.

Cupriavidus necator↗