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At least 433 records · Page 24Linked to original sources

PubMed2005

Selective precipitation of prions by polyoxometalate complexes.

The efficacy of a variety of polyoxometalate anions in selectively precipitating the infectious isoform of the prion protein (PrPSc) over the normal, cellular protein (PrPC) was tested as a means of improving the sensitivity of a conformation-dependent immunoassay (CDI). Experiments utilizing neutralized aqueous solutions containing MgCl2.6H2O and Na2H[PW12O40] (1) indicated that use of the former is detrimental to selectivity, while use of the latter gives optimal selectivity at a concentration of 2.48% w/v, much higher than the 0.31% w/v employed in the current CDI protocol. Similar experiments using Na4[SiW12O40] (2), K5[BW12O40] (3), and Na6[H2W12O40] (4) were performed to probe the role of charge density in polyoxometalate anions possessing the Keggin structure. These, coupled with assignment of solution structures via NMR and infrared spectroscopy, revealed the following trend in optimal concentrations: [HBW11O39]8- < [SiW11O39]8- < [PW11O39]7- = [H2W12O40]6-. Interestingly, use of the salts K10[Zn4(H2O)2(PW9O34)2] (5), Na16[Zn4(H2O)2(P2W15O56)2] (6), and Na27[NaAs4W40O140] (7), containing larger polyoxometalate anions, was found to suppress PrPSc precipitation in a concentration-dependent manner. Taken together, the results suggest a precipitation mechanism wherein Keggin-type anions link multiple PrPSc moieties by binding a somewhat hindered cleft featuring one or more positively charged residues.

Crystallography, X-Ray↗

PubMed2006

Reduction of O2 to superoxide anion (O2.-) in water by heteropolytungstate cluster-anions.

Fundamental information concerning the mechanism of electron transfer from reduced heteropolytungstates (POM(red)) to O2, and the effect of donor-ion charge on reduction of O2 to superoxide anion (O2.-), is obtained using an isostructural series of 1e--reduced donors: alpha-X(n+)W12O40(9-n)-, X(n+) = Al3+, Si4+, P5+. For all three, a single rate expression is observed: -d[POM(red)]/dt = 2k12[POM(red)][O2], where k12 is for the rate-limiting electron transfer from POM(red) to O2. At pH 2 (175 mM ionic strength), k12 increases from 1.4 +/- 0.2 to 8.5 +/- 1 to 24 +/- 2 M-1s-1 as Xn+ is varied from P5+ (3red) to Si4+ (2red) to Al3+ (1red). Variable-pH data (for 1red) and solvent-kinetic isotope (KIE = kH/kD) data (all three ions) indicate that protonated superoxide (HO2.) is formed in two steps--electron transfer, followed by proton transfer (ET-PT mechanism--rather than via simultaneous proton-coupled electron transfer (PCET). Support for an outersphere mechanism is provided by agreement between experimental k12 values and those calculated using the Marcus cross relation. Further evidence is provided by the small variation in k12 observed when Xn+ is changed from P5+ to Si4+ to Al3+, and the driving force for formation of O2.- (aq), which increases as cluster-anion charge becomes more negative, increases by nearly +0.4 V (a decrease of >9 kcal mol-1 in DeltaG degrees ). The weak dependence of k12 on POM reduction potentials reflects the outersphere ET-PT mechanism: as the anions become more negatively charged, the "successor-complex" ion pairs are subject to larger anion-anion repulsions, in the order [(3(ox)3-)(O2.-)]4- < [(2(ox)4-)(O2.-)]5- < [(1(ox)5-)(O2.-)]6-. This reveals an inherent limitation to the use of heteropolytungstate charge and reduction potential to control rates of electron transfer to O2 under turnover conditions in catalysis.

Anions↗

PubMed2002

Distribution of conjugated and free phenols in fruits: antioxidant activity and cultivar variations.

Total and free phenolic contents of 16 commonly consumed fruits (comprising 9 apples, 4 pears, and one each of peach, plum, and kiwi fruit cultivars) were measured by Folin-Ciocalteu assay. Total phenol contents varied from 272 to 475 mg of CtE/100 g of fresh weight. Of the apple cultivars studied, Braeburn and Empire had the highest and lowest total phenol content, respectively. The apple cultivars ranked in the following decreasing order: Braeburn > Red Delicious > Crisp Pink > Granny Smith > Royal Gala > Bramley > Golden Delicious > Fuji > Empire. Among pear cultivars, the order was Forelle > Taylor's > Peckham's > Conference. Peach and plum equally had high contents. The percentage of conjugated phenolics ranged between 3 (Red Delicious) and 77% (Empire) of the total phenols. Comparison of different cultivars of the same fruit and between different fruits showed broad variations in both phenolic content and in vitro antioxidant activity; a weak correlation (R(2) = 0.58) was observed between the phenolic content of the fruits and the total antioxidant activity, as estimated by the FRAP assay. The calculated dietary intake of total, free, and conjugated phenols from average per capita consumption of apples and pears in different regions of the U.K. varied between 104-126, 53-64, and 51-62 mg of CtE/day, respectively.

Antioxidants↗

PubMed2003

Tungsten permanent chemical modifier for fast estimation of Se contents in soil by graphite furnace atomic absorption spectrometry.

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer was used as a modifier for the direct determination of Se in soil extracts by graphite furnace atomic absorption spectrometry. Diethylenetriaminepentaacetic acid (0.0050 mol L(-1)) plus ammonium hydrogencarbonate (1.0 mol L(-1)) extracted predominantly available inorganic selenate from soil. The formation of a large amount of carbonaceous residue inside the atomizer was avoided with a first pyrolysis step at 600 degrees C assisted by air during 30 s. For 20 microL of soil extracts delivered to the atomizer and calibration by matrix matching, an analytical curve (10.0-100 microgram of L(-1)) with good linear correlation (r = 0.999) between integrated absorbance and analyte concentration was established. The characteristic mass was approximately 63 pg of Se, and the lifetime of the tube was approximately 750 firings. The limit of detection was 1.6 microgram L(-1), and the relative standard deviations (n = 12) were typically <4% for a soil extract containing 50 microgram of L(-1). The accuracy of the determination of Se was checked for soil samples by means of addition/recovery tests. Recovery data of Se added to four enriched soil samples varied from 80 to 90% and indicated an accurate method.

Chemical Phenomena↗

PubMed2005

Rapid determination of polyphenols and vitamin C in plant-derived products.

Polyphenols, widely spread in our diet by the consumption of plant food products, are commonly determined using Folin-Ciocalteu reagent that interacts with other different reducing nonphenolic substances and leads to an overestimation of polyphenol content. In this paper we report an optimized Folin-Ciocalteu method to specifically determine the contents of total polyphenols and vitamin C. After the optimal conditions for the colorimetric assay were set, solid-phase extraction (Oasis HLB (hydrophilic-lipophilic balance)) was carried out to eliminate the water-soluble reducing interferences including vitamin C. Colorimetric correction was thus performed by subtracting interfering substances contained in the water washing extract from the raw extract. Moreover, vitamin C present in the water washing extract can be destroyed by heating and thus colorimetrically deduced. This procedure was set up with synthetic solutions and validated on different extracts from fruit products.

Ascorbic Acid↗

PubMed2004

New enzymatic method for the determination of total phenolic content in tea and wine.

A new spectrophotometric enzymatic method for the determination of total phenol content in tea and wine has been developed. The method is based on the peroxidase-catalyzed oxidation, by hydrogen peroxide, of phenols to phenoxyl radicals, which can react with aromatic substrates to form intensely colored adducts. In comparison with the widely used Folin-Ciocalteu method, this method appears to be more specific and more rapid and as a whole is not affected by the common interfering substances such as ascorbate, citrate, and sulfite. Numerous samples of teas and wines were analyzed by using the new method, and the results compared with those obtained by using the Folin and scavenging of DPPH methods. The differences of the total phenols content found by applying the three methods are discussed in terms of the different specificities of the analytical basis.

Colorimetry↗

PubMed2005

Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements.

Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method. This overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. From evaluation of data presented at the First International Congress on Antioxidant Methods in 2004 and in the literature, as well as consideration of potential end uses of antioxidants, it is proposed that procedures and applications for three assays be considered for standardization: the oxygen radical absorbance capacity (ORAC) assay, the Folin-Ciocalteu method, and possibly the Trolox equivalent antioxidant capacity (TEAC) assay. ORAC represent a hydrogen atom transfer (HAT) reaction mechanism, which is most relevant to human biology. The Folin-Ciocalteu method is an electron transfer (ET) based assay and gives reducing capacity, which has normally been expressed as phenolic contents. The TEAC assay represents a second ET-based method. Other assays may need to be considered in the future as more is learned about some of the other radical sources and their importance to human biology.

Antioxidants↗

PubMed2005

Preparation, structure, and electrochemistry of a polypyrrole film doped with manganese(III)-substituted Dawson-type phosphopolyoxotungstate.

The fabrication, structure, electrochemical properties, and electrocatalytic properties of a manganese(III)-substituted Dawson-type phosphopolyoxotungstate, alpha 2-K7P2W17O61(Mn3+.OH2).12H2O (P2W17Mn), entrapped in polypyrrole (PPy) film have been studied. The hybrid film was prepared by potentiostatic polymerization from aqueous solution containing 20 mM pyrrole (Py) and 2 mM P2W17Mn on a pyrolytic graphite (PG) surface. Chronoamperometry, Raman spectroscopy, UV-visible absorption spectroscopy, and cyclic voltammetry were used to monitor and characterize the growth, structure, and properties of the film. The chronoamperometric curve shows that P2W17Mn can catalyze the electrochemical polymerization of Py. The Raman spectrum suggests that the doped P2W17Mn has little effect on the structure of PPy film. The P2W17Mn/PPy film exhibits good voltammetric response in both the acidic aqueous and acetonitrile solutions. At pH 1.0, the molar ratio of pyrrole to P2W17Mn7- in the hybrid film is 21.1:1, quite close to the expected ratio of 21.2:1 for a PPy film with a +0.33 oxidation level per pyrrole moiety and doped with an anion with a charge of 7. The influence of solution pH on P2W17Mn7- in the film is much smaller than that in the aqueous solution. During the potential scanning in 0.1 M LiClO4 acetonitrile solution, P2W17Mn7- was slowly released from the hybrid film and electrolyte ions (Li+ and ClO4-) were inserted into the film. This was identified by cyclic voltammetry and UV-visible spectroscopy. Additionally, the hybrid film can effectively catalyze the reduction of hydrogen peroxide and nitrite.

Anions↗

PubMed2005

Optical spectra of a novel polyoxometalate occluded within modified MCM-41.

The novel polyoxometalate ([(Eu2PW10O38)4(W3O8(H2O)2(OH)4)]22-), also referred to herein as Eu8P4W43, has been immobilized inside the channels of MCM-41 mesoporous molecular sieve material by means of the incipient wetness method. For proper host-guest interaction, amine groups were introduced into the system as a result of an aminosilylation procedure. A stable and integrated Eu8P4W43 polyoxometalate was shown to be formed inside the channels of the modified MCM-41. The products were characterized by XRD, UV-vis absorption, emission, Raman excitation, Raman, and 31P solid-state NMR measurements. Infrared and Raman spectra of the polyoxometalate/MCM-41 composite systems are interpreted as showing spectral shifts due to site induced electrostatic interactions. The photoluminescent behavior of the composite at room temperature indicates a characteristic Eu3+ emission pattern corresponding to 5D0- 7F(J) transitions. A strong photoluminescence suggests the potential utility of the polyoxometalate as a luminescent material.

Aluminum Silicates↗

PubMed2005

Visible-light-induced degradation of rhodamine B by nanosized Bi2WO6.

Visible-light-induced photodegradation of rhodamine B over nanosized Bi2WO6 has been observed. Bi2WO6 exhibited a high photoactivity to photodegrade rhodamine B in the central pH solution under visible irradiation (lambda > 420 nm). After five recycles for the photodegradation of rhodamine B, the catalyst did not exhibit any significant loss of activity, confirming the photocatalyst is essentially stable. The total organic carbon measurement displayed that a high degree of mineralization was achieved in the present photochemical system. The results of density functional theory calculation illuminated that the visible-light absorption band in the Bi2WO6 catalyst is attributed to the band transition from the hybrid orbitals of Bi6s and O2p to the W5d orbitals. The Bi2WO6-assisted photocatalytic degradation of rhodamine occurs via two competitive processes: a photocatalytic process and a photosensitized process. The transformation of rhodamine is mainly via the photocatalytic process. Kinetic studies by using electron spin resonance and the radical scavenger technologies suggest that *OH is not the dominant photooxidant. Direct hole transfers and O2*- could take part in Bi2WO6 photocatalysis. This study provided a possible treatment approach for organic pollutants by using visible light in aqueous ecosystems.

Bismuth↗

PubMed2006

A comparative study of the surface structure, acidity, and catalytic performance of tungstated zirconia prepared from crystalline zirconia or amorphous zirconium oxyhydroxide.

Tungstated zirconias prepared from W deposition on zirconium oxyhydroxide are reportedly active for alkane isomerization, whereas solids synthesized by impregnation of zirconia are inactive. The origin of the differences between the two preparations is not fully understood. The present paper examines the influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performance of WO(x)()/ ZrO(2) catalysts. Two series of catalysts containing W surface densities up to 5.2 at. W/nm(2) were prepared by pore volume impregnation of two different supports: zirconium oxyhydroxide and predominantly tetragonal zirconia (65% tetragonal, 35% monoclinic). The texture and structure of the catalysts were investigated by BET measurements, X-ray diffraction, Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of Zr oxyhydroxide, Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. The development of the acidity was monitored by lutidine adsorption and desorption at 523 K, followed by infrared spectroscopy. The results indicated the presence of a threshold of W surface density at 1.3 at. W/ nm(2) for the detection of these acid sites, followed by a progressive increase in their abundance with increasing W surface density. The development of Brønsted acidity correlated with the evolution of the infrared bands attributed to "extensively" polymerized W species. A direct relationship was observed between the abundance of Brønsted acid sites and the catalytic activity for 2-propanol dehydration. For n-hexane isomerization, compared to 2-propanol dehydration, a higher threshold of W surface densities (3.4 at. W/ nm(2)) for the development of activity was observed. The difference was attributed to stronger Brønsted acid sites required for n-hexane isomerization. The catalysts prepared by impregnation of zirconia exhibited comparable behavior. For a given W surface density, the crystalline composition of the support (tetragonal/monoclinic zirconia), the W surface structure, abundance of Brønsted acid sites, and catalytic performance were similar. Thus, in an apparent variance with some of the results reported in the literature with respect to the influence of preparation methods, no significant effect of the initial form of the support (Zr oxyhydroxide versus predominantly tetragonal zirconia) was evidenced.

Catalysis↗

PubMed2006

Thermotropic mesomorphic behavior of surfactant-encapsulated polyoxometalate hybrids.

We investigate in detail novel organic-inorganic hybrid liquid crystalline materials, the complexes of surfactant-encapsulated polyoxometalate clusters (SECs), using thermal, X-ray diffraction, and FT-IR spectroscopic analyses. The differential scanning calorimetry measurements reveal four phase transitions under heating processes. We employ FT-IR spectroscopy to understand these phase behaviors. On the basis of vibration spectral assignments, the evidence suggests that the first two phase transitions are associated with the increase of gauche conformers and the disruption of alkyl chains packing in the heating run; the third phase transition is due to the full conformational disorder of alkyl chains covered on the polyoxometalates (PMs); no significant C-H stretching or wagging vibrations are observed with the fourth transition. We find that the fourth endothermic peak is sensitive to the charges of the PMs, and the transition temperature decreases from 185, 177, to 164 degrees C with decreasing PM charges from 13, 11, to 9, respectively. Interestingly, the temperatures of the first three phase transitions of SECs are essentially independent of the PM charges.

Calorimetry, Differential Scanning↗

PubMed2005

Photoelectric performance of bacteria photosynthetic proteins entrapped on tailored mesoporous WO3-TiO2 films.

Novel three-dimensional wormlike mesoporous WO(3)-TiO(2) films with tailored pore size (approximately 7.1 nm) were applied to prepare the bio-photoelectrodes (Bio-PEs) through direct entrapping the bacteria photosynthetic reaction center (RC) proteins. These mesoporous WO(3)-TiO(2) films exhibited unique characteristics in the specific loading of RC with high activity retained. Moreover, well-matched energy levels of WO(3)-TiO(2) and RC contributed to the photoelectric performance, especially in the red to near-infrared (NIR) region, of the derived Bio-PEs. Such strategy of manipulating the Bio-PEs based on well-designed mesoporous metal oxides and RC provides an alternative system to probe the photoinduced multiple-pathway electron transfer of photosensitive chromophores, which may open a new perspective to develop versatile bio-photoelectric devices.

Adsorption↗

PubMed1995

Physicochemical mechanism of the interaction between cobalt metal and carbide particles to generate toxic activated oxygen species.

Hard metal alloys (or cemented carbides) are made of a mixture of tungsten carbide particles (WC, more than 80%) cemented in cobalt metal powder (Co, 5-10%). The inhalation of hard metal particles may cause an interstitial pulmonary disease, the mechanism of which involves an interaction between Co and WC particles. Some epidemiological data also suggest that hard metal dust can induce lung cancer in workers. In a macrophage culture model, butylated hydroxytoluene (1 mM) protected from the cytotoxicity of hard metal particles, suggesting a possible involvement of lipid peroxidation in the toxicity of these powders. In a biochemical system, a mixture of Co and WC particles, but not Co or WC alone, stimulated the production of thiobarbituric acid-reactive substances from arachidonic acid. Using a spin trapping system applied to aqueous particulate suspensions and electrochemical techniques, we present experimental evidence that the association of Co and carbide particles represents a specific toxic entity producing large amounts of activated oxygen species. The mechanism of this interaction proceeds through the oxidation of cobalt metal catalyzed at the surface of carbide particles and resulting in the reduction of dissolved oxygen. This physicochemical property of hard metal particles provides a new basis for interpreting their inflammatory action and their possible carcinogenic effect on the lung.

Animals↗

PubMed2004

Effect of the militarily-relevant heavy metals, depleted uranium and heavy metal tungsten-alloy on gene expression in human liver carcinoma cells (HepG2).

Depleted uranium (DU) and heavy-metal tungsten alloys (HMTAs) are dense heavy-metals used primarily in military applications. Chemically similar to natural uranium, but depleted of the higher activity 235U and 234U isotopes, DU is a low specific activity, high-density heavy metal. In contrast, the non-radioactive HMTAs are composed of a mixture of tungsten (91-93%), nickel (3-5%), and cobalt (2-4%) particles. The use of DU and HMTAs in military munitions could result in their internalization in humans. Limited data exist however, regarding the long-term health effects of internalized DU and HMTAs in humans. Both DU and HMTAs possess a tumorigenic transforming potential and are genotoxic and mutagenic in vitro. Using insoluble DU-UO2 and a reconstituted mixture of tungsten, nickel, cobalt (rWNiCo), we tested their ability to induce stress genes in thirteen different recombinant cell lines generated from human liver carcinoma cells (HepG2). The commercially available CAT-Tox (L) cellular assay consists of a panel of cell lines stably transfected with reporter genes consisting of a coding sequence for chloramphenicol acetyl transferase (CAT) under transcriptional control by mammalian stress gene regulatory sequences. DU, (5-50 microg/ml) produced a complex profile of activity demonstrating significant dose-dependent induction of the hMTIIA FOS, p53RE, Gadd153, Gadd45, NFkappaBRE, CRE, HSP70, RARE, and GRP78 promoters. The rWNiCo mixture (5-50 microg/ml) showed dose-related induction of the GSTYA, hMTIIA, p53RE, FOS, NFkappaBRE, HSP70, and CRE promoters. An examination of the pure metals, tungsten (W), nickel (Ni), and cobalt (Co), comprising the rWNiCo mixture, demonstrated that each metal exhibited a similar pattern of gene induction, but at a significantly decreased magnitude than that of the rWNiCo mixture. These data showed a synergistic activation of gene expression by the metals in the rWNiCo mixture. Our data show for the first time that DU and rWNiCo can activate gene expression through several signal transduction pathways that may be involved in the toxicity and tumorigenicity of both DU and HMTAs.

Carcinoma, Hepatocellular↗

PubMed2002

Immunohistochemical study on pulpal response in rat molars after cavity preparation by Er:YAG laser.

While Er:YAG laser systems are in extensive use for caries removal and cavity preparation, the effects of such treatment on pulp tissue remain unclear. This study evaluates these systems using immunohistochemical methods and compares the results with information gained from treatment using conventional burs. Cervical cavities were prepared in the upper first molars of rats, using either an Er:YAG laser or a conventional tungsten-carbide bur. At intervals of 5 min, 6 h, 12 h, 1 d, 3 d and 7 d after cavity preparation, the teeth were processed for immunohistochemical analyses of tissue non-specific alkaline phosphatase, OX6-positive major histocompatibility complex class II antigen-expressing cells and PGP 9.5-immunoreactive nerve fibers. DNA fragmentation was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Tissue non-specific alkaline phosphatase was observed mainly in the subodontoblastic layer under the cavity lesion, from 5 min, in both groups. The immunoreactivity was more pronounced in the laser group, but by 7 d no significant differences were recognizable. At 12 h, TUNEL-positive cells were detected around the odontoblastic layer in both groups. From 3 d to 7 d, a limited number of positive cells were still visible in the group that underwent standard treatment. Clear similarities in the distribution patterns of OX6-immunopositive cells and PGP 9.5-immunoreactive nerve fibers were also noted. From 12 h to 1 d, OX6-positive cells accumulated along the pulp-dentin border, extending their processes into the dentinal tubules. Numerous bead-like PGP 9.5-immunoreactive nerve fibers were observed under the odontoblastic layer at 7 d. These results demonstrated that there was no appreciable difference in the manner in which pulp tissue responded to treatment with either Er:YAG laser or a conventional drill. This would seem to indicate the usefulness of the Er:YAG laser system in the removal of caries and cavity preparation.

Alkaline Phosphatase↗

PubMed1999

Placement of protein and RNA structures into a 5 A-resolution map of the 50S ribosomal subunit.

We have calculated at 5.0 A resolution an electron-density map of the large 50S ribosomal subunit from the bacterium Haloarcula marismortui by using phases derived from four heavy-atom derivatives, intercrystal density averaging and density-modification procedures. More than 300 base pairs of A-form RNA duplex have been fitted into this map, as have regions of non-A-form duplex, single-stranded segments and tetraloops. The long rods of RNA crisscrossing the subunit arise from the stacking of short, separate double helices, not all of which are A-form, and in many places proteins crosslink two or more of these rods. The polypeptide exit channel was marked by tungsten cluster compounds bound in one heavy-atom-derivatized crystal. We have determined the structure of the translation-factor-binding centre by fitting the crystal structures of the ribosomal proteins L6, L11 and L14, the sarcin-ricin loop RNA, and the RNA sequence that binds L11 into the electron density. We can position either elongation factor G or elongation factor Tu complexed with an aminoacylated transfer RNA and GTP onto the factor-binding centre in a manner that is consistent with results from biochemical and electron microscopy studies.

Archaeal Proteins↗

PubMed1994

Crystal structure of Yersinia protein tyrosine phosphatase at 2.5 A and the complex with tungstate.

Protein tyrosine phosphatases (PTPases) and kinases coregulate the critical levels of phosphorylation necessary for intracellular signalling, cell growth and differentiation. Yersinia, the causative bacteria of the bubonic plague and other enteric diseases, secrete an active PTPase, Yop51, that enters and suppresses host immune cells. Though the catalytic domain is only approximately 20% identical to human PTP1B, the Yersinia PTPase contains all of the invariant residues present in eukaryotic PTPases, including the nucleophilic Cys 403 which forms a phosphocysteine intermediate during catalysis. We present here structures of the unliganded (2.5 A resolution) and tungstate-bound (2.6 A) crystal forms which reveal that Cys 403 is positioned at the centre of a distinctive phosphate-binding loop. This loop is at the hub of several hydrogen-bond arrays that not only stabilize a bound oxyanion, but may activate Cys 403 as a reactive thiolate. Binding of tungstate triggers a conformational change that traps the oxyanion and swings Asp 356, an important catalytic residue, by approximately 6 A into the active site. The same anion-binding loop in PTPases is also found in the enzyme rhodanese.

Amino Acid Sequence↗