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At least 19 recordsLinked to original sources
PubMed2004

Dissimilatory arsenate reduction with sulfide as electron donor: experiments with mono lake water and Isolation of strain MLMS-1, a chemoautotrophic arsenate respirer.

Anoxic bottom water from Mono Lake, California, can biologically reduce added arsenate without any addition of electron donors. Of the possible in situ inorganic electron donors present, only sulfide was sufficiently abundant to drive this reaction. We tested the ability of sulfide to serve as an electron donor for arsenate reduction in experiments with lake water. Reduction of arsenate to arsenite occurred simultaneously with the removal of sulfide. No loss of sulfide occurred in controls without arsenate or in sterilized samples containing both arsenate and sulfide. The rate of arsenate reduction in lake water was dependent on the amount of available arsenate. We enriched for a bacterium that could achieve growth with sulfide and arsenate in a defined, mineral medium and purified it by serial dilution. The isolate, strain MLMS-1, is a gram-negative, motile curved rod that grows by oxidizing sulfide to sulfate while reducing arsenate to arsenite. Chemoautotrophy was confirmed by the incorporation of H(14)CO(3)(-) into dark-incubated cells, but preliminary gene probing tests with primers for ribulose-1,5-biphosphate carboxylase/oxygenase did not yield PCR-amplified products. Alignment of 16S rRNA sequences indicated that strain MLMS-1 was in the delta-Proteobacteria, located near sulfate reducers like Desulfobulbus sp. (88 to 90% similarity) but more closely related (97%) to unidentified sequences amplified previously from Mono Lake. However, strain MLMS-1 does not grow with sulfate as its electron acceptor.

Arsenates↗
PubMed2005

Solution structures and backbone dynamics of arsenate reductase from Bacillus subtilis: reversible conformational switch associated with arsenate reduction.

Arsenate reductase encoded by the chromosomal arsC gene in Bacillus subtilis catalyzes the intracellular reduction of arsenate to arsenite, which is then extruded from cells through an efficient and specific transport system. Herein, we present the solution structures and backbone dynamics of both the reduced and oxidized forms of arsenate reductase from B. subtilis. The overall structures of both forms are similar to those of bovine low molecular weight protein-tyrosine phosphatase and arsenate reductase from Staphylococcus aureus. However, several features of the tertiary structure and mobility are notably different between the reduced and oxidized forms of B. subtilis arsenate reductase, particularly in the P-loop region and the segment Cys(82)-Cys(89). The backbone dynamics results demonstrated that the reduced form of arsenate reductase undergoes millisecond conformational changes in the functional P-loop and Cys(82)-Cys(89), which may facilitate the formation of covalent intermediates and subsequent reduction of arsenate. In the oxidized form, Cys(82)-Cys(89) shows motional flexibility on both picosecond-to-nanosecond and possibly millisecond time scales, which may facilitate the reduction of the oxidized enzyme by thioredoxin to regenerate the active enzyme. Overall, the internal dynamics and static structures of the enzyme provide insights into the molecular mechanism of arsenate reduction, especially the reversible conformational switch and changes in internal motions associated with the catalytic reaction.

Arsenates↗
PubMed2005

Assessment of apoptosis in thymocytes and splenocytes from mice exposed to arsenate in drinking water: cytotoxic effects of arsenate on the cells in vitro.

This study provides an assessment of the level of apoptosis in thymocytes and splenocytes from mice exposed to arsenate in drinking water. To simulate the naturally occurring exposure conditions of humans, the animals were exposed to arsenate at the concentrations of 0.5, 5, and 50 mgAs/L. TUNEL method for staining of thymocytes and splenocytes isolated from the mice after 8 and 12 weeks revealed increased percentage of apoptotic cells in the exposed groups. Although statistically significant increases were observed only for the highest concentration of arsenate, the increases showed linear trend as a function of arsenate concentration in drinking water. In vitro experiments performed on isolated cells incubated for 24 hours with arsenate at 6.7-2000 microM showed very similar concentration-viability relationships for both cell populations (IC50 was 442+/-15 microM and 427+/-18 microM for thymocytes and splenocytes, respectively). Arsenate induced a concentration-dependent increase in the percentage of the cells undergoing apoptosis. At higher concentrations, apoptosis was the predominant mode of cell death. It can be speculated that proapoptotic effects of arsenate as observed in our in vivo study may contribute to some immunotoxic symptoms observed in people chronically exposed to arsenic in drinking water.

Animals↗
PubMed2002

Arsenate reductase II. Purine nucleoside phosphorylase in the presence of dihydrolipoic acid is a route for reduction of arsenate to arsenite in mammalian systems.

An arsenate reductase has been partially purified from human liver using ion exchange, molecular exclusion, hydroxyapatite chromatography, preparative isoelectric focusing, and electrophoresis. When SDS-beta-mercaptoethanol-PAGE was performed on the most purified fraction, two bands were obtained. One of these bands was a 34 kDa protein. Each band was excised from the gel and sequenced by LC-MS/MS, and sequest analyses were performed against the OWL database SWISS-PROT with PIR. Mass spectra analysis matched the 34 kDa protein of interest with human purine nucleoside phosphorylase (PNP). The peptide fragments equal to 40.1% of the total protein were 100% identical to the corresponding regions of the human purine nucleoside phosphorylase. Reduction of arsenate in the purine nucleoside arsenolysis reaction required both PNP and dihydrolipoic acid (DHLP). The PNP rate of reduction of arsenate with the reducing agents GSH or ascorbic acid was negligible compared to that with the naturally occurring dithiol DHLP and synthetic dithiols such as BAL (British anti-lewisite), DMPS (2,3-dimercapto-1-propanesulfonate), or DTT (alpha-dithiothreitol). The arsenite production reaction of thymidine phosphorylase had approximately 5% of such PNP activity. Phosphorylase b was inactive. Monomethylarsonate (MMAV) was not reduced by PNP. The experimental results indicate PNP is an important route for the reduction of arsenate to arsenite in mammalian systems.

Animals↗
PubMed1981

Formation of arsenite in lead arsenate or calcium arsenate mixtures.

Lead and calcium arsenates have been used as insecticides in the past with various adjuvants added to increase their effectiveness. Adverse health effects have been reported in industrial situations where these materials were formulated, and packaged, and occasionally used. Reduction of arsenate has been demonstrated to occur when mixtures of lime, lime sulfur, sulfur, and casein were added to lead or calcium arsenate. The formation of soluble arsenite increased with time after the formulations were dry mixed. Levels of soluble arsenite declined in aqueous suspension after 1 day but increased again after 2 months. Total arsenite varied from 0.6 to 2.4% of the arsenic present 253 days after formulation.

Arsenates↗
PubMed2000

Enzymatic reduction of arsenic compounds in mammalian systems: reduction of arsenate to arsenite by human liver arsenate reductase.

An arsenate (As(V)) reductase has been partially purified from human liver. Its apparent molecular mass is approximately 72 kDa. The enzyme required a thiol and a heat stable cofactor for activity. The cofactor is less than 3 kDa in size. The thiol requirement can be satisfied by dithiothreitol (DTT). However, the extent of stimulation of reductase activity by glutathione, thioredoxin, or reduced lipoic acid was negligible compared to that of DTT. The heat stable cofactor does not appear to be Cu(2+), Mn(2+), Zn(2+), Mg(2+), or Ca(2+). The enzyme does not reduce monomethylarsonic acid (MMA(V)). The isolation and characterization of this enzyme demonstrates that in humans, the reduction of arsenate to arsenite is enzymatically catalyzed and is not solely the result of chemical reduction by glutathione as has been proposed in the past.

Adenosine Triphosphatases↗
PubMed2005

Solubility and stability of barium arsenate and barium hydrogen arsenate at 25 degrees C.

The inconsistency among current thermodynamic data of Ba3(AsO4)2(c) and BaHAsO4.H2O(c) led the authors to obtain independent solubility data of barium arsenate by both precipitation and dissolution experiments. Low and neutral pH (3.63-7.43) favored the formation of BaHAsO4.H2O(c). Both BaHAsO4.H2Oc and Ba3(AsO4)2(c) formed at the neutral pH conditions (7.47, 7.66), whereas Ba3(AsO4)2(c) was the only solid phase precipitated at high pH (13.03, 13.10). The Ba3(AsO4)2(c) precipitate acquired at 50 degrees C appeared as small leafy crystal, while the Ba3(AsO4)2(c) solid precipitated at 25 degrees C comprised granular aggregate with some smaller crystal clusters. XRD and SEM analyses of Ba3(AsO4)2(c) and BaHAsO4.H2O(c) indicated that the solids were indistinguishable before and after the dissolution experiments. In the present work, the solubility products (Ksp) for Ba3(AsO4)2(c) and BaHAsO4.H2O(c) were determined to be 10(-23.53)(10(-23.01) to 10(-24.00)) and 10(-5.60)(10(-5.23) to 10(-5.89)), respectively. DeltaGf degrees for Ba3(AsO4)2(c) and BaHAsO4.H2O(c) were calculated to be -3113.40 and -1544.47 kJ/mol, respectively. There was no difference between the solubility products of the leafy and the granular Ba3(AsO4)2(c) solids.

Arsenates↗
PubMed2005

Reduction of arsenate to arsenite by human erythrocyte lysate and rat liver cytosol - characterization of a glutathione- and NAD-dependent arsenate reduction linked to glycolysis.

Reduction of arsenate (AsV) to the more toxic arsenite (AsIII) is of high toxicological importance, yet in vivo relevant enzymes involved have not been identified. Purine nucleoside phosphorylase (PNP) is an efficient AsV reductase in vitro, but its role in AsV reduction is irrelevant in vivo. Intact human red blood cells (RBC) possess an AsV reductase activity that is PNP-independent, diminished by depletion of glutathione (GSH), enhanced by oxidants of erythrocytic NAD(P)H, and possibly linked to the lower part of the glycolytic pathway. In order to characterize this PNP-independent AsV reductase activity further, we examined the effects of GSH, inorganic phosphate, some inhibitors of glucose metabolism, glycolytic substrates, and pyridine, as well as adenine nucleotides on AsV reduction in lysed RBC and rat liver cytosol in the presence of BCX-1777, a PNP inhibitor. In hemolysate, GSH enhanced AsV reduction in a concentration-dependent manner, whereas phosphate inhibited it. Glycolytic substrates, especially fructose-1,6-bisphosphate and phosphoglyceric acids, improved AsV reductase activity. NAD, especially together with these substrates, strongly increased AsIII formation, whereas NADH strongly inhibited it. NADP and adenine nucleotides diminished, while 2-phosphoglycollate, which increases the breakdown of the RBC-specific compound 2,3-bisphosphoglycerate to 3-phosphoglycerate, doubled the AsV reductase activity. Although AsV reduction by the liver cytosol responded similarly to GSH, NAD, and glycolytic substrates as in the hemolysate, it was barely influenced by NADH, was diminished by 2-phosphoglycollate, and was stimulated by NADP. Collectively, hemolysate and rat liver cytosol possess a PNP-independent AsV reductase activity. This enzymatic activity requires GSH, NAD, and glycolytic substrates, and purportedly involves one or both of the two functionally linked glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase. In addition, the data presented here suggest that yet another PNP-independent AsV reductase resides in the hepatic cytosol. Although this latter enzyme remains unknown, identification of the AsV reductase depending on GSH, NAD, and glycolytic substrates is presented in the following paper.

Adenosine Diphosphate↗
PubMed2005

Effect of an inactivator of glyceraldehyde-3-phosphate dehydrogenase, a fortuitous arsenate reductase, on disposition of arsenate in rats.

The environmentally prevalent arsenate (AsV) is reduced in the body to the much more toxic arsenite (AsIII). Recently, we have demonstrated that the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyzes the reduction of AsV in the presence of glutathione, yet the role of GAPDH in AsV reduction in vivo is unknown. Therefore, we examined the effect of (S)-alpha-cholorhydrin (ACH), which forms a GAPDH-inhibitory metabolite, on the reduction of AsV in rats. These studies confirmed the in vitro role of GAPDH as an AsV reductase, inasmuch as 3 h after administration of ACH (100 or 200 mg/kg, ip) to rats both the cytosolic GAPDH activity and the AsV-reducing activity dramatically fell in the liver, moderately decreased in the kidneys, and remained unchanged in the muscle. Moreover, the AsV-reducing activity closely correlated with the GAPDH activity in the hepatic cytosols of control and ACH-treated rats. Two confounding effects of ACH (i.e., a slight fall in hepatic glutathione levels and a rise in urinary AsV excretion) prompted us to examine its influence on the disposition of injected AsV (50 micromol/kg, iv) in rats with ligated bile duct as well as in rats with ligated bile duct and renal pedicles. These experiments demonstrated that the hepatic retention of AsV significantly increased, and the combined levels of AsV metabolites (i.e., AsIII plus methylated arsenicals) in the liver decreased in response to ACH; however, ACH failed to delay the disappearance of AsV from the blood of rats with blocked excretory routes. Thus, the GAPDH inactivator ACH inhibits AsV reduction by the liver, but not by the whole body, probably because the impaired hepatic reduction is compensated for by hepatic and extrahepatic AsV-reducing mechanisms spared by ACH. It is most likely that ACH inhibits hepatic AsV reduction predominantly by inactivating GAPDH in the liver; however, a slight ACH-induced glutathione depletion may also contribute. While this study seems to support the conclusion that GAPDH in the liver is involved in AsV reduction in rats, confirmation of the in vivo role of GAPDH as an AsV reductase is desirable.

Animals↗
PubMed2003

The distribution of arsenate and arsenite in shoots and roots of Holcus lanatus is influenced by arsenic tolerance and arsenate and phosphate supply.

The recent discovery that phytochelatins are important for arsenic (As) detoxification in terrestrial plants results in the necessity to understand As speciation and metabolism in plant material. A hydroponic study was therefore conducted to examine the effects of different levels of phosphate and arsenate [As(V)] on As speciation and distribution in tolerant and non-tolerant clones of Holcus lanatus. Speciation of As in tissue (using high-performance liquid chromatography-inductively coupled plasma mass spectrometry) revealed that the predominant species present were the inorganic As species (As(V) and arsenite [As(III)]), although small levels (<1%) of organic As species (dimethylarsinic acid and monomethylarsonic acid) were detected in shoot material. In roots, the proportion of total As present as As(III) generally increased with increasing levels of As(V) in the nutrient solution, whereas in shoots, the proportion of total As present as As(III) generally decreased with increasing levels of As(V). H. lanatus plants growing in the high-phosphorus (P) (100 micro M) solution contained a higher proportion of As(V) (with regard to total As) in both roots and shoots than plants supplied with low P (10 micro M); in addition, tolerant clones generally contained a higher proportion of As(V) with regard to total As than non-tolerant clones. The study further revealed that As(V) can be reduced to As(III) in both roots and shoots. Although the reduction capacity was limited, the reduction was closely regulated by As influx for all treatments. The results therefore provide a new understanding about As metabolism in H. lanatus.

Arsenates↗
PubMed2006

Enhanced arsenate reduction by a CDC25-like tyrosine phosphatase explains increased phytochelatin accumulation in arsenate-tolerant Holcus lanatus.

Decreased arsenate [As(V)] uptake is the major mechanism of naturally selected As(V) hypertolerance in plants. However, As(V)-hypertolerant ecotypes also show enhanced rates of phytochelatin (PC) accumulation, suggesting that improved sequestration might additionally contribute to the hypertolerance phenotype. Here, we show that enhanced PC-based sequestration in As(V)-hypertolerant Holcus lanatus is not due to an enhanced capacity for PC synthesis as such, but to increased As(V) reductase activity. Vacuolar transport of arsenite-thiol complexes was equal in both ecotypes. Based on homology with the yeast As(V) reductase, Acr2p, we identified a Cdc25-like plant candidate, HlAsr, and confirmed the As(V) reductase activity of both HlAsr and the homologous protein from Arabidopsis thaliana. The gene appeared to be As(V)-inducible and its expression was enhanced in the As(V)-hypertolerant H. lanatus ecotype, compared with the non-tolerant ecotype. Homologous ectopic overexpression of the AtASR cDNA in A. thaliana produced a dual phenotype. It improved tolerance to mildly toxic levels of As(V) exposure, but caused hypersensitivity to more toxic levels. Arabidopsis asr T-DNA mutants showed increased As(V) sensitivity at low exposure levels and enhanced arsenic retention in the root. It is argued that, next to decreased uptake, enhanced expression of HlASR might act as an additional determinant of As(V) hypertolerance and As transport in H. lanatus.

Amino Acid Sequence↗