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Petru Pascuta - One of the best experts on this subject based on the ideXlab platform.
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novel structural properties of the lead vanadate Tellurate glass ceramics
Journal of Materials Science, 2010Co-Authors: M. Rada, E. Culea, S. Rada, Vistrian Maties, Petru PascutaAbstract:In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–Tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–Tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO2·4V2O5], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–Tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te2V2 5+O9, Pb3(V5+O4)2, Pb2V2 5+O7, and V2O5-rich amorphous phase. On the other hand, these glass ceramics contain V4+ and V5+ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V4+=O bonds are created by two different mechanisms: the first of reduction of V5+ ions to V4+ ions and thus of creation of V4+=O bonds.
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Novel structural properties of the lead–vanadate–Tellurate glass ceramics
Journal of Materials Science, 2009Co-Authors: Marius Rada, Simona Rada, Eugen Culea, Vistrian Maties, Petru PascutaAbstract:In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–Tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–Tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO2·4V2O5], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–Tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te2V2 5+O9, Pb3(V5+O4)2, Pb2V2 5+O7, and V2O5-rich amorphous phase. On the other hand, these glass ceramics contain V4+ and V5+ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V4+=O bonds are created by two different mechanisms: the first of reduction of V5+ ions to V4+ ions and thus of creation of V4+=O bonds.
Claudio C. Vásquez - One of the best experts on this subject based on the ideXlab platform.
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Tellurite reduction by Escherichia coli NDH-II dehydrogenase results in superoxide production in membranes of toxicant-exposed cells
BioMetals, 2014Co-Authors: Waldo A. Díaz-vásquez, María J. Abarca-lagunas, Felipe A. Arenas, Camilo A. Pinto, Fabián A. Cornejo, Poorna T. Wansapura, Gayan A. Appuhamillage, Thomas G. Chasteen, Claudio C. VásquezAbstract:Tellurite, the most soluble tellurium oxyanion, is extremely harmful for most microorganisms. Part of this toxicity is due to the generation of reactive oxygen species that in turn cause oxidative stress. However, the way in which tellurite interferes with cellular processes is not well understood to date. Looking for new cellular tellurite targets, we decided to evaluate the functioning of the electron transport chain in tellurite-exposed cells. In this communication we show that the E. coli ndh gene, encoding NDH-II dehydrogenase, is significantly induced in toxicant-exposed cells and that the enzyme displays tellurite-reducing activity that results in increased superoxide levels in vitro.
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A comparative study of tellurite toxicity in normal and cancer cells
Molecular & Cellular Toxicology, 2012Co-Authors: Juan M. Sandoval, Claudio C. Vásquez, Julien Verrax, Pedro Buc CalderonAbstract:Data regarding tellurium (Te) toxicity are scarce but metabolic studies in bacteria highlight a major role of reactive oxygen species (ROS). Concentration- and time-dependent cell death has been reported in cancer cells exposed to inorganic tellurite. However, the potential in vitro effect that tellurite could generates in non-transformed human cells is still unknown. Therefore, we have studied the toxicity of inorganic tellurite (K_2TeO_3) in both freshly isolated peripheral blood leukocytes and in human chronic myeloid leukemia cells (K562 cells). Interestingly, we observed higher increases of ROS in leukocytes after treatment with tellurite, as compared to K562 cells. Given the high reactivity of tellurite with glutathione (GSH), a mechanism that leads to ROS formation (and mainly superoxide anion), we postulate that such a difference between cancer and normal cells is likely due to the higher GSH contents found in leukocytes versus leukemia cells. Taken together, our data point out the major differences that can be observed between cancer and corresponding normal cells in studies looking for in vitro toxicity.
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Tellurite-induced oxidative stress leads to cell death of murine hepatocarcinoma cells
BioMetals, 2010Co-Authors: Juan M. Sandoval, Claudio C. Vásquez, Philippe Levêque, Bernard Gallez, Pedro Buc CalderonAbstract:Data regarding tellurium (Te) toxicity are scarce. Studies on its metabolism, performed mainly in bacteria, underline a major role of reactive oxygen species (ROS). We investigated whether tellurite undergoes redox cycling leading to ROS formation and cancer cell death. The murine hepatocarcinoma Transplantable Liver Tumor (TLT) cells were challenged with tellurite either in the presence or in the absence of different compounds as N -acetylcysteine (NAC), 3-methyladenine, BAPTA-AM, and catalase. NAC inhibition of tellurite-mediated toxicity suggested a major role of oxidative stress. Tellurite also decreased both glutathione (GSH) and ATP content by 57 and 80%, respectively. In the presence of NAC however, the levels of such markers were almost fully restored. Tellurite-mediated ROS generation was assessed both by using the fluorescent, oxidation-sensitive probe dichlorodihydrofluorescein diacetate (DCHF-DA) and electron spin resonance (ESR) spectroscopy to detect hydroxyl radical formation. Cell death occurs by a caspase-independent mechanism, as shown by the lack of caspase-3 activity and no cleavage of poly(ADP-ribose)polymerase (PARP). The presence of γ-H2AX suggests tellurite-induced DNA strand breaking, NAC being unable to counteract it. Although the calcium chelator BAPTA-AM did show no effect, the rapid phosphorylation of eIF2α suggests that, in addition to oxidative stress, an endoplasmic reticulum (ER) stress may be involved in the mechanisms leading to cell death by tellurite.
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the dihydrolipoamide dehydrogenase of aeromonas caviae st exhibits nadh dependent tellurite reductase activity
Biochemical and Biophysical Research Communications, 2008Co-Authors: Miguel E. Castro, Roberto C Molina, Waldo A Diaz, Sergio Pichuantes, Claudio C. VásquezAbstract:Abstract Potassium tellurite (K2TeO3) is extremely toxic for most forms of life and only a limited number of organisms are naturally resistant to the toxic effects of this compound. Crude extracts prepared from the environmental isolate Aeromonas caviae ST catalize the in vitro reduction of TeO 3 2 - in a NADH-dependent reaction. Upon fractionation by ionic exchange column chromatography three major polypeptides identified as the E1, E2, and E3 components of the pyruvate dehydrogenase (PDH) complex were identified in fractions exhibiting tellurite-reducing activity. Tellurite reductase and pyruvate dehydrogenase activities co-eluted from a Sephadex gel filtration column. To determine which component(s) of the PDH complex has tellurite reductase activity, the A. caviae ST structural genes encoding for E1 (aceE), E2 (aceF), and E3 (lpdA) were independently cloned and expressed in Escherichia coli and their gene products purified. Results indicated that tellurite reductase activity lies almost exclusively in the E3 component, dihydrolipoamide dehydrogenase. The E3 component of the PDH complex from E. coli, Zymomonas mobilis, Streptococcus pneumoniae, and Geobacillus stearothermophilus also showed NADH-dependent tellurite reductase in vitro suggesting that this enzymatic activity is widely distributed among microorganisms.
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Capillary electrophoretic determination of selenocyanate and selenium and tellurium oxyanions in bacterial cultures.
Analytical biochemistry, 2007Co-Authors: Bala Krishna Pathem, Claudio C. Vásquez, Gonzalo A. Pradenas, Miguel E. Castro, Thomas G. ChasteenAbstract:A simple capillary zone electrophoretic method for the determination of biospherically important oxyanions of selenium (Se) and tellurium and another Se-containing anion, selenocyanate, has been developed. The method uses direct UV absorption detection. Time course experiments with time slices as short as 6 min are possible. This method's detection limits and linear range compare well with other methods involving samples containing complex biological matrices. The metalloid-containing anions examined were selenocyanate, selenite, selenate, tellurite, and Tellurate. We applied this method to live cultures of two different bacteria in two different growth media in time course experiments following the changes in metalloid-containing anion concentrations. The results show that this method is a useful means of following the biological processing of these analytes in bacterial cultures.
Thomas G. Chasteen - One of the best experts on this subject based on the ideXlab platform.
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Tellurite reduction by Escherichia coli NDH-II dehydrogenase results in superoxide production in membranes of toxicant-exposed cells
BioMetals, 2014Co-Authors: Waldo A. Díaz-vásquez, María J. Abarca-lagunas, Felipe A. Arenas, Camilo A. Pinto, Fabián A. Cornejo, Poorna T. Wansapura, Gayan A. Appuhamillage, Thomas G. Chasteen, Claudio C. VásquezAbstract:Tellurite, the most soluble tellurium oxyanion, is extremely harmful for most microorganisms. Part of this toxicity is due to the generation of reactive oxygen species that in turn cause oxidative stress. However, the way in which tellurite interferes with cellular processes is not well understood to date. Looking for new cellular tellurite targets, we decided to evaluate the functioning of the electron transport chain in tellurite-exposed cells. In this communication we show that the E. coli ndh gene, encoding NDH-II dehydrogenase, is significantly induced in toxicant-exposed cells and that the enzyme displays tellurite-reducing activity that results in increased superoxide levels in vitro.
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Capillary electrophoretic determination of selenocyanate and selenium and tellurium oxyanions in bacterial cultures.
Analytical biochemistry, 2007Co-Authors: Bala Krishna Pathem, Claudio C. Vásquez, Gonzalo A. Pradenas, Miguel E. Castro, Thomas G. ChasteenAbstract:A simple capillary zone electrophoretic method for the determination of biospherically important oxyanions of selenium (Se) and tellurium and another Se-containing anion, selenocyanate, has been developed. The method uses direct UV absorption detection. Time course experiments with time slices as short as 6 min are possible. This method's detection limits and linear range compare well with other methods involving samples containing complex biological matrices. The metalloid-containing anions examined were selenocyanate, selenite, selenate, tellurite, and Tellurate. We applied this method to live cultures of two different bacteria in two different growth media in time course experiments following the changes in metalloid-containing anion concentrations. The results show that this method is a useful means of following the biological processing of these analytes in bacterial cultures.
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Geobacillus stearothermophilus V ubiE gene product is involved in the evolution of dimethyl telluride in Escherichia coli K-12 cultures amended with potassium Tellurate but not with potassium tellurite
JBIC Journal of Biological Inorganic Chemistry, 2004Co-Authors: Manuel A. Araya, Thomas G. Chasteen, Jerry W. Swearingen, Mary F. Plishker, Claudia P. Saavedra, Claudio C. VásquezAbstract:A 3.8-kb fragment of chromosomal DNA of Geobacillus stearothermophilus V cloned in pSP72 (p1VH) confers resistance to potassium tellurite (K_2TeO_3) and to potassium Tellurate (K_2TeO_4) when the encoded genes are expressed in Escherichia coli K-12. The nt sequence of the cloned fragment predicts three ORFs of 780, 399, and 600 bp, whose encoded protein products exhibit about 80% similarity with the SUMT methyltransferase and the BtuR protein of Bacillus megaterium , and with the UbiE methyltransferase of Bacillus anthracis A2012, respectively. In addition, E . coli /p1VH cells evolved dimethyl telluride, which was released into the headspace gas above liquid cultures when amended with K_2TeO_3 or with K_2TeO_4. After 48 h of growth in the presence of these compounds, a protein of about 25 kDa was found at a significantly higher level when crude extracts were analyzed by SDS-PAGE. The N-terminal amino acid (aa) sequence of this protein, obtained by Edman degradation, matched the deduced aa sequence predicted by the G . stearothermophilus V ubiE gene. This gene was amplified by PCR, subcloned in pET21b, and transformed into E . coli JM109(DE3). Interestingly, DMTe evolution occurred when these modified cells were grown in K_2TeO_4 – but not in K_2TeO_3 – amended media. These results may be indicative that the two Te oxyanions could be detoxified in the cell by different metabolic pathways.
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Production of dimethyl telluride and elemental tellurium by bacteria amended with tellurite or Tellurate
Applied Organometallic Chemistry, 2001Co-Authors: Rukma S. T. Basnayake, Janet H. Bius, Osman M. Akpolat, Thomas G. ChasteenAbstract:The purpose of this study was to determine whether a facultative anaerobe, Pseudomonas fluorescens K27, would produce dimethyl telluride when anaerobic cultures were amended with differing concentrations of sodium Tellurate and/or sodium tellurite and how that volatile organotellurium production varied over time. Batch bacterial bioreactor experiments were undertaken in order to observe the changes in the headspace of a growth medium solution inoculated with P. fluorescens and amended with tellurium salts. Gas samples were taken from the bioreactor every hour and were analyzed by capillary gas chromatography using fluorine-induced chemiluminescence detection to determine compounds in the headspace. Liquid samples were analyzed by spectrophotometer to determine optical densities, which were used as an indicator of cell growth. Verification of the identity of the dimethyl telluride produced in the bacterial headspace above a Tellurate-amended culture was achieved by comparison with the chromatographic retention time of an authentic (CH3)2Te standard and by gas chromatography/mass spectrometry. The time course production of dimethyl telluride varied with amendment salts' tellurium oxidation states and concentrations. Increasing Tellurate concentrations caused slower bacterial growth, but those cultures reached the stationary phase sooner than cultures amended with tellurite concentrations 10 or 100 times less. Black elemental tellurium (Te0) was produced by live cultures amended with tellurium salts but not by sterile controls. The amount of tellurium in the solid phase (as Te0 and in/or on cells) harvested from replicate, anaerobic cultures of P. fluorescens sampled after 92 h of incubation was approximately 34%. Mixed tellurite/Tellurate amendment experiments exhibited a synergistic toxic effect and yielded less final biomass and very little dimethyl telluride production compared with cultures amended with either Tellurate or tellurite alone. Copyright © 2001 John Wiley & Sons, Ltd.
Marius Rada - One of the best experts on this subject based on the ideXlab platform.
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The experimental and theoretical investigations on the structure of the gadolinium-lead-Tellurate glasses
Materials Chemistry and Physics, 2011Co-Authors: Simona Rada, E. Culea, Marius RadaAbstract:The purpose of this paper was to approach the structure of gadolinium–lead–Tellurate glasses with compositions xGd2O3 (100 − x)[7TeO2·3PbO], x = 0–90 mol% using the X-ray diffraction, DFT calculations, FTIR, EPR and UV–VIS spectroscopy. Our results show that the doping with gadolinium ions will deform the Te–O–Te linkages, will affect the length of Te O bonds and the accommodation of the network with excess of oxygen will be realized by the reorganization of the Tellurate structural units. These affinities pronounced of the lead and gadolinium cations towards tellurium atoms yield the formation of the Pb2Te3O8 and Gd2Te6O15 crystalline phases because Tellurate structural units can adopt a variety of structures due to the presence of the lone-pair electrons. © 2011 Elsevier B.V. All rights reserved.
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Novel structural properties of the lead–vanadate–Tellurate glass ceramics
Journal of Materials Science, 2009Co-Authors: Marius Rada, Simona Rada, Eugen Culea, Vistrian Maties, Petru PascutaAbstract:In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–Tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–Tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO2·4V2O5], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–Tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te2V2 5+O9, Pb3(V5+O4)2, Pb2V2 5+O7, and V2O5-rich amorphous phase. On the other hand, these glass ceramics contain V4+ and V5+ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V4+=O bonds are created by two different mechanisms: the first of reduction of V5+ ions to V4+ ions and thus of creation of V4+=O bonds.
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Infrared spectroscopic and DFT investigations of the vanadate-Tellurate glasses structures.
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2009Co-Authors: Simona Rada, Marius Rada, Eugen CuleaAbstract:Abstract Vanadate–Tellurate vitreous systems with composition (1 − x )TeO 2 · x V 2 O 5 where x = 0.3 and 0.4 have been prepared by the conventional melt-quench method. The structural aspects have been investigated using FTIR spectroscopy and the density functional theory (DFT) calculations. The present study provides the interesting information concerning devitrification behavior of the vanadate–Tellurate vitreous system which occur Te 2 V 2 O 9 crystalline phase. The structure of the heat-treated glasses was found to consist mainly of rings containing [TeO 3 ], [TeO 4 ], [VO 4 ] and some [VO 5 ] structural units.
Vladimir Yurkov - One of the best experts on this subject based on the ideXlab platform.
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Bioremediation potential of bacteria able to reduce high levels of selenium and tellurium oxyanions
Archives of Microbiology, 2018Co-Authors: Chris Maltman, Vladimir YurkovAbstract:Environmental contamination by Te and Se oxyanions has become a serious concern, with the search for green, ecologically friendly methods for removal gaining ground. Bacteria capable of reducing these highly toxic compounds to a virtually non-toxic elemental form could provide a solution. In this study, four strains of bacteria with potential for bioremediation of Te and Se oxyanions were investigated. Under aerobic conditions over 48 h, Erythromicrobium ramosum , strain E5 removed 244 µg/ml tellurite and 98 µg/ml selenite, Erythromonas ursincola , KR99 203 µg/ml tellurite and 100 µg/ml selenite, AV-Te-18 98 µg/ml tellurite and 103 µg/ml selenite and ER-V-8 93 µg/ml tellurite and 103 µg/ml selenite. In the absence of oxygen, AV-Te-18 and ER-V-8 removed 10 µg/ml tellurite after 24 and 48 h, respectively and 46 and 25 µg/ml selenite, respectively, over 48 h. ER-V-8 removed 14 µg/ml selenate after 5 days. This highlights the great potential of these microbes for use in bioremediation.
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Bioremediation potential of bacteria able to reduce high levels of selenium and tellurium oxyanions
Archives of Microbiology, 2018Co-Authors: Chris Maltman, Vladimir YurkovAbstract:Environmental contamination by Te and Se oxyanions has become a serious concern, with the search for green, ecologically friendly methods for removal gaining ground. Bacteria capable of reducing these highly toxic compounds to a virtually non-toxic elemental form could provide a solution. In this study, four strains of bacteria with potential for bioremediation of Te and Se oxyanions were investigated. Under aerobic conditions over 48 h, Erythromicrobium ramosum , strain E5 removed 244 µg/ml tellurite and 98 µg/ml selenite, Erythromonas ursincola , KR99 203 µg/ml tellurite and 100 µg/ml selenite, AV-Te-18 98 µg/ml tellurite and 103 µg/ml selenite and ER-V-8 93 µg/ml tellurite and 103 µg/ml selenite. In the absence of oxygen, AV-Te-18 and ER-V-8 removed 10 µg/ml tellurite after 24 and 48 h, respectively and 46 and 25 µg/ml selenite, respectively, over 48 h. ER-V-8 removed 14 µg/ml selenate after 5 days. This highlights the great potential of these microbes for use in bioremediation.
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Two distinct periplasmic enzymes are responsible for tellurite/Tellurate and selenite reduction by strain ER-Te-48 associated with the deep sea hydrothermal vent tube worms at the Juan de Fuca Ridge black smokers
Archives of Microbiology, 2017Co-Authors: Chris Maltman, Lynda J. Donald, Vladimir YurkovAbstract:Strain ER-Te-48 isolated from a deep-ocean hydrothermal vent tube worm is capable of resisting and reducing extremely high levels of tellurite, Tellurate, and selenite, which are used for respiration anaerobically. Tellurite and Tellurate reduction is accomplished by a periplasmic enzyme of 215 kDa comprised of 3 subunits (74, 42, and 25 kDa) in a 2:1:1 ratio. The optimum pH and temperature for activity is 8.0 and 35 °C, respectively. Tellurite reduction has a V _max of 5.6 µmol/min/mg protein and a K _m of 3.9 mM. In the case of the Tellurate reaction, V _max and K _m were 2.6 µmol/min/mg protein and 2.6 mM, respectively. Selenite reduction is carried out by another periplasmic enzyme with a V _max of 2.8 µmol/min/mg protein, K _m of 12.1 mM, and maximal activity at pH 6.0 and 38 °C. This protein is 165 kDa and comprised of 3 subunits of 98, 44, and 23 kDa in a 1:1:1 ratio.
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two distinct periplasmic enzymes are responsible for tellurite Tellurate and selenite reduction by strain er te 48 associated with the deep sea hydrothermal vent tube worms at the juan de fuca ridge black smokers
Archives of Microbiology, 2017Co-Authors: Chris Maltman, Lynda J. Donald, Vladimir YurkovAbstract:Strain ER-Te-48 isolated from a deep-ocean hydrothermal vent tube worm is capable of resisting and reducing extremely high levels of tellurite, Tellurate, and selenite, which are used for respiration anaerobically. Tellurite and Tellurate reduction is accomplished by a periplasmic enzyme of 215 kDa comprised of 3 subunits (74, 42, and 25 kDa) in a 2:1:1 ratio. The optimum pH and temperature for activity is 8.0 and 35 °C, respectively. Tellurite reduction has a V max of 5.6 µmol/min/mg protein and a K m of 3.9 mM. In the case of the Tellurate reaction, V max and K m were 2.6 µmol/min/mg protein and 2.6 mM, respectively. Selenite reduction is carried out by another periplasmic enzyme with a V max of 2.8 µmol/min/mg protein, K m of 12.1 mM, and maximal activity at pH 6.0 and 38 °C. This protein is 165 kDa and comprised of 3 subunits of 98, 44, and 23 kDa in a 1:1:1 ratio.
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tellurite and Tellurate reduction by the aerobic anoxygenic phototroph erythromonas ursincola strain kr99 is carried out by a novel membrane associated enzyme
Microorganisms, 2017Co-Authors: Chris Maltman, Lynda J. Donald, Vladimir YurkovAbstract:Erythromonas ursincola, strain KR99 isolated from a freshwater thermal spring of Kamchatka Island in Russia, resists and reduces very high levels of toxic tellurite under aerobic conditions. Reduction is carried out by a constitutively expressed membrane associated enzyme, which was purified and characterized. The tellurite reductase has a molecular weight of 117 kDa, and is comprised of two subunits (62 and 55 kDa) in a 1:1 ratio. Optimal activity occurs at pH 7.0 and 28 °C. Tellurite reduction has a Vmax of 5.15 µmol/min/mg protein and a Km of 3.36 mM. The enzyme can also reduce Tellurate with a Vmax and Km of 1.08 µmol/min/mg protein and 1.44 mM, respectively. This is the first purified membrane associated Te oxyanion reductase.
