Showing papers on "Vanadate published in 2005"

Structure of the ABC transporter MsbA in complex with ADP.vanadate and lipopolysaccharide.

Abstract: Select members of the adenosine triphosphate (ATP)-binding cassette (ABC) transporter family couple ATP binding and hydrolysis to substrate efflux and confer multidrug resistance. We have determined the x-ray structure of MsbA in complex with magnesium, adenosine diphosphate, and inorganic vanadate (Mg·ADP·Vi) and the rough-chemotype lipopolysaccharide, Ra LPS. The structure supports a model involving a rigid-body torque of the two transmembrane domains during ATP hydrolysis and suggests a mechanism by which the nucleotide-binding domain communicates with the transmembrane domain. We propose a lipid “flip-flop” mechanism in which the sugar groups are sequestered in the chamber while the hydrophobic tails are dragged through the lipid bilayer.

Colloidal nanoparticles of Ln3+-doped LaVO4: energy transfer to visible- and near-infrared-emitting lanthanide ions.

Abstract: Colloidal, organic solvent-soluble Ln3+-doped LaVO4 nanoparticles have been synthesized by a precipitation reaction in the presence of (C18H37O)2PS2- as ligand, that coordinates to the surface of the nanoparticles The materials are well soluble in chlorinated solvent such as chloroform Energy transfer of excited vanadate groups has been observed for Ln3+ ions that emit in the visible and the near-infrared (Eu3+, Tm3+, Nd3+, Er3+, Ho3+, Dy3+, Sm3+, Pr3+), thus making it a very generic sensitization mechanism The LaVO4 nanoparticles have a different crystal structure than bulk LaVO4 ones (xenotime instead of monazite), similar to YVO4 nanoparticles This xenotime crystal structure results in a more asymmetric crystal field around the Ln3+ ions that is advantageous to their luminescence, for it increases the radiative rate constant, thus reducing quenching processes

Citrate Secretion Coupled with the Modulation of Soybean Root Tip under Aluminum Stress. Up-Regulation of Transcription, Translation, and Threonine-Oriented Phosphorylation of Plasma Membrane H+-ATPase

Abstract: The aluminum (Al)-induced secretion of citrate has been regarded as an important mechanism for Al resistance in soybean (Glycine max). However, the mechanism of how Al induces citrate secretion remains unclear. In this study, we investigated the regulatory role of plasma membrane H+-ATPase on the Al-induced secretion of citrate from soybean roots. Experiments performed with plants grown in full nutrient solution showed that Al-induced activity of plasma membrane H+-ATPase paralleled secretion of citrate. Vanadate and fusicoccin, an inhibitor and an activator, respectively, of plasma membrane H+-ATPase, exerted inhibitory and stimulatory effects on the Al-induced secretion of citrate. Higher activity of plasma membrane H+-ATPase coincided with more citrate secretion in Al-resistant than Al-sensitive soybean cultivars. These results suggested that the effects of Al stress on citrate secretion were mediated via modulation of the activity of plasma membrane H+-ATPase. The relationship between the Al-induced secretion of citrate and the activity of plasma membrane H+-ATPase was further demonstrated by analysis of plasma membrane H+-ATPase transgenic Arabidopsis (Arabidopsis thaliana). When plants were grown on Murashige and Skoog medium containing 30 μm Al (9.1 μm Al3+ activity), transgenic plants exuded more citrate compared with wild-type Arabidopsis. Results from real-time reverse transcription-PCR and immunodetection analysis indicated that the increase of plasma membrane H+-ATPase activity by Al is caused by transcriptional and translational regulation. Furthermore, plasma membrane H+-ATPase activity and expression were higher in an Al-resistant cultivar than in an Al-sensitive cultivar. Al activated the threonine-oriented phosphorylation of plasma membrane H+-ATPase in a dose- and time-dependent manner. Taken together, our results demonstrated that up-regulation of plasma membrane H+-ATPase activity was associated with the secretion of citrate from soybean roots.

Dioxovanadium(v) complexes of ONO donor ligands derived from pyridoxal and hydrazides: Models of vanadate-dependent haloperoxidases

Abstract: [VO(acac)2] reacts with H2L [H2L are the hydrazones H2pydx-inh (I), H2pydx-nh (II), or H2pydx-bhz (III); pydx = pyridoxal, inh = isonicotinohydrazide, nh = nicotinohydrazide, bhz = benzohydrazide] in dry methanol to yield the oxovanadium(IV) complexes [VOL] (H2L = I: 1; H2L = II: 4) or [VO(pydx-bhz)]. These complexes, when exposed to air, convert into the corresponding dioxovanadium(V) complexes [VO2HL] (H2L = I: 2; H2L = II: 5; H2L = III: 7). Aqueous solutions of vanadate and the ligands at pH = 7.5 give rise to the formation of [K(H2O)3][VO2(pydx-inh)] (3), [K(H2O)2][VO2(pydx-nh)] (6) and [K(H2O)2][VO2(pydx-bhz)] (8). Treatment of 6 and 8 with H2O2 generates the oxo(peroxo)vanadium complexes [VO(O2)L] (H2L = II: 9; H2L = III: 10). Complexes 9 and 10 are capable of transferring an oxo group to PPh3. Acidification of 8 with HCl afforded a hydroxo(oxo) complex. The crystal and molecular structures of ligand I and complex 3 have been solved by single-crystal X-ray diffraction. In the anion 3, the vanadium atom is in a distorted tetragonal-pyramidal environment (τ = 0.23). The K+ ion is coordinated to four water molecules (two of which bridge to a neighbouring K+ ion), the pyridine nitrogen atom of an isonicotinic moiety, the equatorial oxo group of the VO2+ fragment, and the alcoholic group of the pyridoxal moiety, which links adjacent layers in the three-dimensional lattice network. In the presence of KBr/H2O2, the anionic complexes 3, 6 and 8 catalyse the oxidative bromination of salicylaldehyde in water to 5-bromosalicylaldehyde in ca. 40% yields with ca. 87% selectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Respiration and Growth of Shewanella oneidensis MR-1 Using Vanadate as the Sole Electron Acceptor

Abstract: Shewanella oneidensis MR-1 is a free-living gram-negative gamma-proteobacterium that is able to use a large number of oxidizing molecules, including fumarate, nitrate, dimethyl sulfoxide, trimethylamine N-oxide, nitrite, and insoluble iron and manganese oxides, to drive anaerobic respiration. Here we show that S. oneidensis MR-1 is able to grow on vanadate as the sole electron acceptor. Oxidant pulse experiments demonstrated that proton translocation across the cytoplasmic membrane occurs during vanadate reduction. Proton translocation is abolished in the presence of protonophores and the inhibitors 2-heptyl-4-hydroxyquinoline N-oxide and antimycin A. Redox difference spectra indicated the involvement of membrane-bound menaquinone and cytochromes c, which was confirmed by transposon mutagenesis and screening for a vanadate reduction-deficient phenotype. Two mutants which are deficient in menaquinone synthesis were isolated. Another mutant with disruption in the cytochrome c maturation gene ccmA was unable to produce any cytochrome c and to grow on vanadate. This phenotype could be restored by complementation with the pEC86 plasmid expressing ccm genes from Escherichia coli. To our knowledge, this is the first report of E. coli ccm genes being functional in another organism. Analysis of an mtrB-deficient mutant confirmed the results of a previous paper indicating that OmcB may function as a vanadate reductase or may be part of a vanadate reductase complex.

A density functional theory study of the mechanism of free radical generation in the system vanadate/PCA/H2O2.

Abstract: Experimental studies by Shul'pin and co-workers have shown that vanadate anions in combination with pyrazine-2-carboxylic acid (PCA ≡ pcaH) produce an exceptionally active complex that promotes the oxidation of alkanes and other organic molecules. Reaction of this complex with H2O2 releases HOO• free radicals and generates V(IV) species, which are capable of generating HO• radicals by reaction with additional H2O2. The oxidation of alkanes is initiated by reaction with the HO• radicals. The mechanism of hydrocarbon oxidation with vanadate/PCA/H2O2 catalyst has been studied using density functional theory. The proposed model reproduces the major experimental observations. It is found that a vanadium complex with one pca (PCA ≡ pcaH) and one H2O2 ligand is the precursor to the species responsible for HOO• generation. It is also found that species containing two pca ligands and an H2O2 molecule do not exist in the solution, in contradiction to previous interpretations of experimental observations. Calculated...

Alterations in the α2 isoform of Na,K-ATPase associated with familial hemiplegic migraine type 2

Abstract: A number of missense mutations in the Na,K-ATPase α2 catalytic subunit have been identified in familial hemiplegic migraine with aura. Two alleles (L764P and W887R) showed loss-of-function, whereas a third (T345A) is fully functional but with altered Na,K-ATPase kinetics. This study describes two additional mutants, R689Q and M731T, originally identified by Vanmolkot et al. [Vanmolkot, K. R., et al. (2003) Ann. Neurol. 54, 360-366], which we show here to also be functional and kinetically altered. Both mutants have reduced catalytic turnover and increased apparent affinity for extracellular K+. For both R689Q and M731T, sensitivity to vanadate inhibition is decreased, suggesting that the steady-state E1 ↔ E2 poise of the enzyme is shifted toward E1. Whereas the K′ATP is not affected by the R689Q replacement, the M731T mutant has an increase in apparent affinity for ATP. Analysis of the structural changes effected by T345A, R689Q, and M731T mutations, based on homologous replacements in the known crystal structure of the sarcoplasmic reticulum Ca-ATPase, provides insights into the molecular bases for the kinetic alterations. It is suggested that the disease phenotype is the consequence of lowered molecular activity of the α2 pump isoform due to either decreased K+ affinity (T345A) or catalytic turnover (R689Q and M731T), thus causing a delay in extracellular K+ clearance and/or altered localized Ca2+ handling/signaling secondary to reduced activity in colocalized Na+/Ca2+ exchange.

Nanophase Iron Phosphate, Iron Arsenate, Iron Vanadate, and Iron Molybdate Minerals Synthesized within the Protein Cage of Ferritin

Abstract: Nanoparticles of iron phosphate, iron arsenate, iron molybdate, and iron vanadate were synthesized within the 8 nm interior of ferritin. The synthesis involved reacting Fe(II) with ferritin in a buffered solution at pH 7.4 in the presence of phosphate, arsenate, vanadate, or molybdate. O2 was used as the oxidant to deposit the Fe(III) mineral inside ferritin. The rate of iron incorporation into ferritin was stimulated when oxo-anions were present. The simultaneous deposition of both iron and the oxo-anion was confirmed by elemental analysis and energy-dispersive X-ray analysis. The ferritin samples containing iron and one of the oxo-anions possessed different UV/vis spectra depending on the anion used during mineral formation. TEM analysis showed mineral cores with approximately 8 nm mineral particles consistent with the formation of mineral phases inside ferritin.

Amelioration of altered antioxidant status and membrane linked functions by vanadium and Trigonella in alloxan diabetic rat brains.

Abstract: Trigonella foenum graecum seed powder (TSP) and sodium orthovanadate (SOV) have been reported to have antidiabetic effects. However, SOV exerts hypoglycemic effects at relatively high doses with several toxic effects. We used low doses of vanadate in combination with TSP and evaluated their antidiabetic effects on anti-oxidant enzymes and membrane-linked functions in diabetic rat brains. In rats, diabetes was induced by alloxan monohydrate (15 mg/100 g body wt.) and they were treated with 2 IU insulin, 0.6 mg/ml SOV, 5% TSP and a combination of 0.2 mg/ml SOV with 5% TSP for 21 days. Blood glucose levels, activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), Na+/K+ ATPase, membrane lipid peroxidation and fluidity were determined in different fractions of whole brain after 21 days of treatment. Diabetic rats showed high blood glucose (P less than 0.001), decreased activities of SOD, catalase and Na+/K+ ATPase (P less than 0.01, P less than 0.001 and P less than 0.01), increased levels of GPx and MDA (P less than 0.01 and P less than 0.001) and decreased membrane fluidity (P less than 0.01). Treatment with different antidiabetic compounds restored the above-altered parameters. Combined dose of Trigonella and vanadate was found to be the most effective treatment in normalizing these alterations. Lower doses of vanadate could be used in combination with TSP to effectively counter diabetic alterations without any toxic effects.

The role of Ca2+ transport across the plasma membrane for cell migration.

Abstract: Cell migration plays a central role in many physiological and pathophysiological processes. On a cellular level it is based on a highly coordinated restructuring of the cytoskeleton, a continuous cycle of adhesion and de-adhesion as well as on the activity of ion channels and transporters. The cytoplasmic Ca2+ ([Ca2+]i) concentration is an important coordinator of these intracellular processes. Thus, [Ca2+]i must be tightly controlled in migrating cells. This is among other things achieved by the activity of Ca2+ permeable channels, the plasma membrane Ca2+-ATPase (PMCA) and the Na+/Ca2+ exchanger (NCX) in the plasma membrane. Here, we wanted to determine the functional role of these transport proteins in cell migration. We therefore quantified the acute effect of inhibitors of these transport proteins (Gd3+, vanadate, KB-R7943) on migration, [Ca2+]i, and intracellular pH (pHi) of MDCK-F cells. Migration was monitored with computer-assisted time-lapse video microscopy. [Ca2+]i and pHi were measured with the fluorescent indicators fura-2 and BCECF. NCX expression in MDCK-F cells was verified with ion substitution experiments, and expression of PMCA was tested with RT-PCR. All blockers lead to a rapid impairment of cell migration. However, the most prominent effect is elicited by NCX-inhibition with KB-R7943. NCX-blockade leads to an almost complete inhibition of migration which is accompanied by a dose-dependent increase of [Ca2+]i and an intracellular alkalinisation. We show that inhibition of NCX and PMCA strongly affects lamellipodial dynamics of migrating MDCK-F cells. Taken together, our results show that PMCA and in particular NCX are of critical importance for cell migration.

Quantum Mechanics/Molecular Mechanics Calculations of the Vanadium Dependent Chloroperoxidase

Abstract: Large quantum mechanics/molecular mechanics (QM/MM) calculations are used to probe the resting and initial protonated states of the vanadium dependent chloroperoxidase from the pathogenic fungus Curvularia inaequalis QSite was used to model 433 residues and 24 structural waters with molecular mechanics, while 8 active-site residues and the vanadate cofactor (161 atoms) were represented at the B3LYP/lacvp* level of theory Our previous study of small model systems implied that the resting state of the enzyme contains a trigonal bipyramidal vanadate with one hydroxyl group in the equatorial plane and another in the axial position This study uses a much larger model of the biological system at a higher level of theory to identify the location of the equatorial hydroxo group with respect to the enzyme active site We also identify a second resting-state configuration with an axial water and three equatorial oxo moieties that is nearly isoenergetic with the previously identified state We propose that the resting state is a hybrid of these two configurations, stabilized by the long-range electrostatic field of the protein environment The first step in catalysis is believed to be protonation of the vanadate Our previous small models indicated that there were two protonated configurations, but this study shows that the configuration containing an axial water and one hydroxo group in the equatorial plane is significantly lower in energy than any other configuration Additionally, we can now assign an important role for lysine 353 in the catalytic cycle Based on our calculations and other model studies, we provide an updated catalytic cycle for vanadium dependent haloperoxidase activity Further, we demonstrate the importance of system set up In particular, maintaining the proper electrostatic field at the active site is crucial for identifying the correct minima in a truncated protein model

Protective Action of Vanadate at Defected Areas of Organic Coatings on Zinc

Abstract: The kinetics of vanadate release from an organic coating and the stability and protective ability of the newly formed vanadate-based films on zinc surfaces have been studied with respect to self-healing ability of vanadate-pigmented organic coatings. The results were compared with those obtained with chromate. The kinetics of vanadate release from a polyester coating was comparable to that of chromate. The methods of X-ray absorption near edge spectroscopy (XANES) and scanning Kelvin probe were used for studying the mechanism of inhibition and the kinetics of vanadate reduction on bare zinc. XANES proved to be a powerful tool for determination of the oxidation state of vanadium in surface films. The experiments showed that vanadate was reduced more rapidly than chromate under the same atmospheric conditions. However, addition of magnesium phosphate resulted in a significantly lower reduction rate of vanadate. The results are discussed in light of the increased adsorption ability of the more negatively charged vanadium(V) species at higher pH, while the oxygen reduction process on zinc is inhibited due to the presence of phosphate. Thus, vanadate in combination with another inhibitor could provide corrosion protection at defects of organic coatings on zinc comparable to that of chromate.

Synthesis of vanadium(IV,V) hydroxamic acid complexes and in vivo assessment of their insulin-like activity.

Abstract: We synthesized vanadyl (oxidation state +IV) and vanadate (oxidation state +V) complexes with the same hydroxamic acid derivative ligand, and assessed their glucose-lowering activities in relation to the vanadium biodistribution behavior in streptozotocin-induced diabetic mice. When the mice received an intraperitoneal injection of the complexes, the vanadate complex more effectively lowered the elevated glucose levels compared with the vanadyl one. The glucose-lowering effect of the vanadate complex was linearly related to its dose within the range from 2.5 to 7.5 mg V/kg. In addition, pretreatment of the vanadate complex induced a larger insulin-enhancing effect than the vanadyl complex. Both complexes were more effective than the corresponding inorganic vanadium compounds. The vanadyl and vanadate complexes, but not the inorganic vanadium compounds, resulted in almost the same organ vanadium distribution. Consequently, the observed differences in the insulin-like activity between the complexes would reflect the potency of the two compounds in the +IV and +V oxidation states in the subcellular region.

Heat generation in Nd doped vanadate crystals with 1.34 μm laser action

Abstract: Thermal load in Nd3+ doped vanadate crystals with and without laser action at 1.34 mum is investigated. Excited state absorption contributes significantly to a fractional thermal loading as well as quantum defect.

Curcumin modulation of Na,K-ATPase: phosphoenzyme accumulation, decreased K+ occlusion, and inhibition of hydrolytic activity

Abstract: 1 Curcumin, the major constitute of tumeric, is an important nutraceutical that has been shown to be useful in the treatment of many diseases. As an inhibitor of the sarcoplasmic reticulum Ca(2+)-ATPase, curcumin was shown to correct cystic fibrosis (CF) defects in some model systems, whereas others have reported no or little effects on CF after curcumin treatment, suggesting that curcumin effect is not due to simple inhibition of the Ca(2+)-ATPase. 2 We tested the hypothesis that curcumin may modulate other members of the P(2)-type ATPase superfamily by studying the effects of curcumin on the activity and kinetic properties of the Na,K-ATPase. 3 Curcumin treatment inhibited Na,K-ATPase activity in a dose-dependent manner (K(0.5) approximately 14.6 microM). Curcumin decreased the apparent affinity of Na,K-ATPase for K(+) and increased it for Na(+) and ATP. Kinetic analyses indicated that curcumin induces a three-fold reduction in the rate of E1P --> E2P transition, thereby increasing the steady-state phosphoenzyme level. Curcumin treatment significantly abrogated K(+) occlusion to the enzyme as evidenced from kinetic and proteolytic cleavage experiments. Curcumin also significantly decreased the vanadate sensitivity of the enzyme. 4 Thus, curcumin partially blocks the K(+) occlusion site, and induces a constitutive shift in the conformational equilibrium of the enzyme, towards the E1 conformation. 5 The physiological consequences of curcumin treatment previously reported in different epithelial model systems may, at least in part, be related to the direct effects of curcumin on Na,K-ATPase activity.

Growth Inhibition by Tungsten in the Sulfur-Oxidizing Bacterium Acidithiobacillus thiooxidans

Abstract: Growth of five strains of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans, including strain NB1-3, was inhibited completely by 50 μM of sodium tungstate (Na2WO4). When the cells of NB1-3 were incubated in 0.1 M β-alanine–SO4 2− buffer (pH 3.0) with 100 μM Na2WO4 for 1 h, the amount of tungsten bound to the cells was 33 μg/mg protein. Approximately 10 times more tungsten was bound to the cells at pH 3.0 than at pH 7.0. The tungsten binding to NB1-3 cells was inhibited by oxyanions such as sodium molybdenum and ammonium vanadate. The activities of enzymes involved in elemental sulfur oxidation of NB1-3 cells such as sulfur oxidase, sulfur dioxygenase, and sulfite oxidase were strongly inhibited by Na2WO4. These results indicate that tungsten binds to NB1-3 cells and inhibits the sulfur oxidation enzyme system of the cells, and as a result, inhibits cell growth. When portland cement bars supplemented with 0.075% metal nickel and with 0.075% metal nickel and 0.075% calcium tungstate were exposed to th...

A supramolecular fluorescence sensor for pyrovanadate as a functional model of vanadium haloperoxidase.

Abstract: A novel basket-shaped tris(pyrene guanidinium) receptor was synthesized which binds pyrovanadate and pyrophosphate with Ka > 107 M-1. The binding of both anions is associated with quenching of the excimer fluorescence of the pyrenes. The supramolecular vanadate complex catalyzes the bromination of activated C−H bonds and hence is an enzyme mimic of vanadium haloperoxidases.

TD-DFT studies on the electronic structure of imidazole bound vanadate in vanadium containing haloperoxidases (VHPO)

Abstract: Time dependent density functional theory (TD-DFT) is utilized to study the electronic structure of the active site of vanadium containing haloperoxidases (VHPOs). Calculations on the species, modeled for pentacoordination of the vanadium atom as found in the active site of the enzyme are performed for different geometries and protonation states of the vanadate moiety. Calculations are also carried out on structures in which vanadate is surrounded by all of the seven amino acid residues which constitute the active site of the enzyme. Two such structures with mono and doubly protonated vanadate were considered. Excitations calculated by TD-DFT, using statistical average of the orbital model exchange-correlation potential (SAOP), reveal that the excitation behavior of doubly protonated vanadate species located in the protein model matrix closely resembles the experimentally observed optical transition for the holoenzyme. Implications of the hydrogen bonding interactions through the protein environment as well as the variation of the protonation state of the active site vanadate are discussed. For the vanadate a rather large distortion from the idealized trigonal bipyramidal arrangement is observed.