Effects of bilirubin configurational photoisomers on the measurement of direct bilirubin by the vanadate oxidation method.

BACKGROUND: Direct-reacting bilirubin concentrations measured using vanadate chemical oxidation method do not exactly match the conjugated bilirubin concentration. One of the causes is the effect of bilirubin photoisomers. However, the quantitative evaluation of the effects of these photoisomers has not been sufficiently conducted. In particular, the influence of bilirubin configurational isomers on direct bilirubin is the most critical factor. METHODS: Sixteen residual serum samples were used. For quantitative analysis based on the change in direct bilirubin and bilirubin configurational isomer, samples were irradiated via blue light-emitting diodes to suppress the production of bilirubin structural isomers. Total bilirubin and direct bilirubin concentrations were measured using the vanadate chemical oxidation method. Concentrations of 4Z,15Z-bilirubin IXα and its photoisomers were measured using high-performance liquid chromatography. The sum of 4Z,15E-bilirubin IXα and 4E,15Z-bilirubin IXα was notated as bilirubin configurational isomer, and the differences between the measured values of the irradiated and non-irradiated samples were calculated and notated as ΔDB and ΔBCI. RESULTS: In non-irradiated and irradiated samples, total bilirubin and direct bilirubin concentrations were 10.73 mg/dL with significant a decrease to 10.60 mg/dL and 0.69 mg/dL with a significant increase to 0.78 mg/dL, while bilirubin configurational isomer values were 1.00 mg/dL and 1.52 mg/dL, respectively. The linear regression equation revealed a significant positive correlation of Y = 0.187X-0.006 between ΔDB (Y) and ΔBCI (X). CONCLUSION: Applying the vanadate chemical oxidation method affected approximately 19% of the bilirubin configurational isomer concentration for direct bilirubin. Extreme caution is necessary when interpreting the measured values of samples indicative of unconjugated hyperbilirubinaemia.

Evaluating the effects of vanadyl sulfate on biomarkers of oxidative stress and inflammation in renal tissue of rats with diabetes type 2

Vanadyl sulfate (VS) is an ingredient in some food supplements and experimental drugs. This study was designed to assay the effects of VS on biomarkers of oxidative stress and inflammation in renal tissue of rats with diabetes type 2. 30 male Wistar rats were divided into three equal groups as follow: non-diabetics, non-treated diabetics and VS-treated diabetics. Diabetes type 2 has been induced through high fat diet and fructose in the animals. Diabetic rats were treated with 25 mg/kgBW of VS in water for 12 weeks. At the end of study, glucose and insulin were measured using commercially available kits in serum and biomarkers of oxidative stress and inflammation in renal homogenates of animals were measured by related methods. Compared to controls, glucose and insulin were increased significantly in non-treated diabetic rats (p-value <0.05) that showed the induction of diabetes type 2 in rats. The results showed that in VS-treated diabetic rats compared to the non-treated diabetic group, vanadyl sulfate significantly reduced the glucose and insulin secretion and changed renal inflammatory and oxidative markers, except protein carbonyl so that we couldn't find any significant changes. Our study showed that vanadyl supplementation had positive effects on oxidative stress and inflammation biomarkers in kidney of diabetic rats

A selective electrochemical sensor for caffeic acid and photocatalyst for metronidazole drug pollutant - A dual role by rod-like SrV2O6.

In the present study, well-defined one-dimensional (1D) rod-like strontium vanadate (SrV2O6) was prepared by simple hydrothermal method without using any other surfactants/templates. The successful formation of rod-like SrV2O6 was confirmed by various analytical and spectroscopic techniques. Interestingly, for the first time the dual role of as-prepared rod-like SrV2O6 were employed as an electrochemical sensor for the detection of caffeic acid (CA) as well as visible light active photocatalyst for the degradation of metronidazole (MNZ) antibiotic drug. As an electrochemical sensor, the SrV2O6 modified glassy carbon electrode (GCE) demonstrated a superior electrocatalytic activity for the detection of CA by chronoamperometry and cyclic voltammetry (CVs). In addition, the electrochemical sensor exhibited a good current response for CA with excellent selectivity, wide linear response range, lower detection limit and sensitivity of 0.01-207 µM, 4 nM and 2.064 µA µM-1cm-2, respectively. On the other hand, as-synthesized rod-like SrV2O6 showed highly efficient and versatile photocatalytic performances for the degradation of MNZ, which degrades above 98% of MNZ solution under visible light irradiation within 60 min. The obtained results evidenced that the improvement of rod-like SrV2O6 might be a resourceful electrocatalyst and photocatalyst material in the probable applications of environmental and biomedical applications.

Extending the functionality of the slurry ferrihydrite-DGT method: Performance evaluation for the measurement of vanadate, arsenate, antimonate and molybdate in water.

The monitoring of oxyanions in waters, presents significant challenges due to their relatively low concentrations, and a characteristically changeable/unstable/reactive geochemistry with high spatial and temporal turnover. This results in a very heterogeneous pattern of mobility and bioavailability, which is difficult to capture reliably and in a cost effective manner. The diffusive gradients in thin-films (DGT) technique is a popular analytical tool for testing water quality, primarily because it provides a time-integrated measurement. However, to date, the most widely used DGT configuration for oxyanion sampling, the slurry ferrihydrite binding layer (SF-DGT) has only been fully characterized for phosphate. Confirmatory testing of the functional range of ionic strengths, pH, deployment times and ionic competition effects, that the SF-DGT's operates within has not been carried out, but is addressed in this study for VV, AsV, SbV, and MoVI. In this study SF-DGT SbV measurements functioned over the largest range of conditions (ionic strength, 0.1-500 mM; pH 3.86-9.90), while ionic strengths above 100 and 500 mM were found to be problematic for AsV and MoVI, respectively. Low pH (below 4) caused inferences with VV, conversely AsV and MoVI determination faltered/deviated from predicted responses in pH conditions of ∼9. SF-DGT measurements adequately predicted up to weeklong averaged in situ metal oxyanion concentrations in a freshwater river. This study concludes that the SF-DGT configuration is highly suitable for pollution monitoring applications in freshwater systems for key oxyanion species.

(51)V NMR investigation of cell-associated vanadate species in Phycomyces blakesleeanus mycelium.

(51)V NMR spectroscopy was used for detection and identification of cell-associated vanadate (V(5+)) species after exposure of Phycomyces blakesleeanus mycelium, in exponential phase of growth, to sodium orthovanadate. Complete disappearance of monomer and dimer signals and decreased intensity of the tetramer signal were observed about 40 min after treatment. Simultaneously, a signal at -532 ppm, with increasing intensity, was detected in spectra. The time-dependent rise in this signal was connected to a decrease in the extracellular monomer signal, indicating its transport into the cell. The signal at -532 ppm did not belong to any known simple oxido-vanadate species, nor to a complex with any of the components of experimental medium. This signal was the only one present in spectrum of the mycelium washed 35 min after treatment, and the only one observed in mycelium cultivated on vanadate-contained medium. Therefore, its appearance can be attributed to intracellular complexation, and may represent an important detoxification mechanism of the cell exposed to a physiologically relevant concentration of vanadate. Experiments ((51)V NMR and polarography) performed with Cd-pretreated mycelium (inhibitor of an enzyme responsible for V(5+) reduction) and ferricyanide-preincubated mycelium excluded the possibility of V(5+) tetramer's entry into the cell.

Simultaneous speciation analysis of chromate, molybdate, tungstate and vanadate in welding fume alkaline extracts by HPLC-ICP-MS.

A novel analytical procedure was developed for the simultaneous speciation analysis of chromate, molybdate, tungstate and vanadate by anion-exchange high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Linear gradient elution from 100% water to 100% 0.7 M NaCl was applied for chromatographic separation of metal species. In standard aqueous solution at neutral pH molybdate, tungstate and vanadate exist in several aqueous species, while chromate is present as a single CrO4(2-) species. Consequently, only chromate can be separated from this solution in a sharp chromatographic peak. For obtaining sharp chromatographic peaks for molybdate, tungstate and vanadate, the pH of aqueous standard solutions was raised to 12. At highly alkaline conditions single CrO4(2-), MoO4(2-) and WO4(2-) are present and were eluted in sharp chromatographic peaks, while VO4(3-) species, which predominates at pH 12 was eluted in slightly broaden peak. In a mixture of aqueous standard solutions (pH 12) chromate, molybdate, tungstate and vanadate were eluted at retention times from 380 to 420 s, 320 to 370 s, 300 to 350 s and 240 to 360 s, respectively. Eluted species were simultaneously detected on-line by ICP-MS recording m/z 52, 95, 182 and 51. The developed procedure was successfully applied to the analysis of leachable concentrations of chromate, molybdate, tungstate and vanadate in alkaline extracts (2% NaOH+3% Na2CO3) of manual metal arc (MMA) welding fumes loaded on filters. Good repeatability and reproducibility of measurement (RSD±3.0%) for the investigated species were obtained in both aqueous standard solutions (pH 12) and in alkaline extracts of welding fumes. Low limits of detection (LODs) were found for chromate (0.02 ng Cr mL(-1)), molybdate (0.1 ng Mo mL(-1)), tungstate (0.1 ng W mL(-1)) and vanadate (0.2 ng V mL(-1)). The accuracy of analytical procedure for the determination of chromate was checked by analysis of CRM 545, Cr(VI) in welding dust loaded on a filter. Good agreement between determined and reported certified values was obtained. For molybdate, tungstate and vanadate the assessment of accuracy was performed by spiking welding fume filters. Good recoveries for all investigated species (98-101%) confirmed the accuracy of the analytical procedure.

Biotransformations of Antidiabetic Vanadium Prodrugs in Mammalian Cells and Cell Culture Media: A XANES Spectroscopic Study.

The antidiabetic activities of vanadium(V) and -(IV) prodrugs are determined by their ability to release active species upon interactions with components of biological media. The first X-ray absorption spectroscopic study of the reactivity of typical vanadium (V) antidiabetics, vanadate ([V(V)O4](3-), A) and a vanadium(IV) bis(maltolato) complex (B), with mammalian cell cultures has been performed using HepG2 (human hepatoma), A549 (human lung carcinoma), and 3T3-L1 (mouse adipocytes and preadipocytes) cell lines, as well as the corresponding cell culture media. X-ray absorption near-edge structure data were analyzed using empirical correlations with a library of model vanadium(V), -(IV), and -(III) complexes. Both A and B ([V] = 1.0 mM) gradually converged into similar mixtures of predominantly five- and six-coordinate V(V) species (∼75% total V) in a cell culture medium within 24 h at 310 K. Speciation of V in intact HepG2 cells also changed with the incubation time (from ∼20% to ∼70% V(IV) of total V), but it was largely independent of the prodrug used (A or B) or of the predominant V oxidation state in the medium. Subcellular fractionation of A549 cells suggested that V(V) reduction to V(IV) occurred predominantly in the cytoplasm, while accumulation of V(V) in the nucleus was likely to have been facilitated by noncovalent bonding to histone proteins. The nuclear V(V) is likely to modulate the transcription process and to be ultimately related to cell death at high concentrations of V, which may be important in anticancer activities. Mature 3T3-L1 adipocytes (unlike for preadipocytes) showed a higher propensity to form V(IV) species, despite the prevalence of V(V) in the medium. The distinct V biochemistry in these cells is consistent with their crucial role in insulin-dependent glucose and fat metabolism and may also point to an endogenous role of V in adipocytes.

Vanadium bioavailability in soils amended with blast furnace slag.

Blast furnace (BF) slags are commonly applied as soil amendments and in road fill material. In Sweden they are also naturally high in vanadium. The aim of this study was to assess the vanadium bioavailability in BF slags when applied to soil. Two soils were amended with up to 29% BF slag (containing 800 mg V kg(-1)) and equilibrated outdoors for 10 months before conducting a barley shoot growth assay. Additional soil samples were spiked with dissolved vanadate(V) for which assays were conducted two weeks (freshly spiked) and 10 months (aged) after spiking. The BF slag vanadium was dominated by vanadium(III) as shown by V K-edge XANES spectroscopy. In contrast, results obtained by HPLC-ICP-MS showed that vanadium(V), the most toxic vanadium species, was predominant in the soil solution. Barley shoot growth was not affected by the BF slag additions. This was likely due to limited dissolution of vanadium from the BF slag, preventing an increase of dissolved vanadium above toxic thresholds. The difference in vanadium bioavailability among treatments was explained by the vanadium concentration in the soil solution. It was concluded that the vanadium in BF slag is sparingly available. These findings should be of importance in environmental risk assessment.

Rapid speciation and determination of vanadium compounds using ion-pair reversed-phase ultra-high-performance liquid chromatography inductively coupled plasma-sector field mass spectrometry.

Environmental vanadium contamination is a potential concern to public health, as evidenced by its place on the U.S. Environmental Protection Agency Drinking Water Contaminant Candidate List as a priority contaminant. Vanadium toxicity varies significantly between different oxidation states; therefore, it is crucial to be able to monitor the speciation of vanadium in environmental samples. In this study, a novel method is described that utilizes ion-pair reversed-phase ultra-high-performance liquid chromatography with inductively coupled plasma-sector field mass spectrometry (IP-RP-UHPLC-ICP-SFMS) to separate vanadyl and vanadate ions and resolve a major polyatomic spectral interference ((35)Cl(16)O(+)) in less than a minute. Detection limits were obtained in the low ngL(-1) (part per trillion) range with linear calibrations across several orders of magnitude (50ngL(-1)-100µgL(-1)). The mechanism of chromatographic retention was elucidated through investigation of the role of ethylenediaminetetraacetic acid, tetrabutylammonium ion and pH on elution. The optimized method was then applied to the speciation of vanadium in local lake water samples.

Raman spectroscopy of the multi anion mineral arsentsumebite Pb2Cu(AsO4)(SO4)(OH) and in comparison with tsumebite Pb2Cu(PO4)(SO4)(OH).

The mineral arsentsumebite Pb(2)Cu(AsO(4))(SO(4))(OH), a copper arsenate-sulphate hydroxide of the brackebuschite group has been characterised by Raman spectroscopy. The brackebuschite mineral group are a series of monoclinic arsenates, phosphates and vanadates of the general formula A(2)B(XO(4))(OH,H(2)O), where A may be Ba, Ca, Pb, Sr, while B may be Al, Cu(2+),Fe(2+), Fe(3+), Mn(2+), Mn(3+), Zn and XO(4) may be AsO(4), PO(4), SO(4),VO(4). Bands are assigned to the stretching and bending modes of SO(4)(2-) AsO(4)(3-) and HOAsO(3) units. Raman spectroscopy readily distinguishes between the two minerals arsentsumebite and tsumebite. Raman bands attributed to arsenate are not observed in the Raman spectrum of tsumebite. Phosphate bands found in the Raman spectrum of tsumebite are not found in the Raman spectrum of arsentsumebite. Raman spectroscopy readily distinguishes the two minerals tsumebite and arsentsumebite.

Sorption characteristics and mechanisms of oxyanions and oxyhalides having different molecular properties on Mg/Al layered double hydroxide nanoparticles.

The sorption ability of fast-coprecipitated and hydrothermally-treated Mg/Al layered double hydroxide nanoparticles (FCHT-LDH) for various oxyhalides and oxyanions was evaluated. Interactions of oxyhalide such as monovalent bromate or oxyanions such as divalent chromate and divalent vanadate with FCHT-LDH were investigated using a combination of macroscopic (batch sorption/desorption studies and electrophoretic mobility (EM) measurements) and microscopic techniques (CHNS/O, XRD, FTIR, XPS, and EXAFS analyses). The sorption studies on various oxyanions and oxyhalides suggested that their sorption characteristics on FCHT-LDH were largely governed by their ionic potentials and molecular structures. Oxyanions which have ionic potentials higher than 7 nm(-1) were found to be more readily sorbed by FCHT-LDH than oxyhalides with ionic potentials lower than 5 nm(-1). The results obtained also demonstrated that trigonal pyramid oxyhalides showed a lower degree of specificity for FCHT-LDH than the tetrahedral coordinated oxyanions. From the macroscopic and microscopic studies, monovalent oxyhalide sorption on FCHT-LDH was postulated to occur mainly via anion exchange mechanism with subsequent formation of outer-sphere surface complexes. For polyvalent oxyanion sorption on FCHT-LDH, the mechanisms were possibly associated with both anion exchange and ligand exchange reactions, resulting in the coexistence of outer-sphere and inner-sphere surface complexes.

EPR spectra of Cu2+ and VO2+ ions in ammonium hydrogen oxalate hemihydrate [(NH4)HC2O4 . (1/2)H2O] single crystals.

Cu(2+) and VO(2+) doped ammonium hydrogen oxalate hemihydrate, [(NH(4))HC(2)O(4) . (1/2)H(2)O], single crystals have been studied at room temperature and at 113K in three mutually perpendicular planes. Both ions yield unexpectedly large number of lines. The calculated results of the Cu(2+) and VO(2+) doped in [(NH(4))HC(2)O(4) . (1/2)H(2)O] indicate that both ions substitute with the NH(4)(+) ion in the structure. The EPR spectra of Cu(2+) ions are characteristic of tetragonally elongated octahedral site and the spectra of VO(2+) are characteristic of tetragonally compressed complex. The angular variation of the EPR spectra has shown that two different Cu(2+) and VO(2+) complexes are located in different chemical environments, and each environment contains two magnetically inequivalent Cu(2+) and VO(2+) sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal g and the hyperfine (A) values of both ions are determined.

Separation via flotation, spectrophotometric speciation, and determination of vanadium(IV) in wastes of power stations.

1-(2-Hydroxy-4-methoxybenzophenone)-4-phenylthiosemicarbazone (HMBPT) was investigated as a new reagent for the flotation of vanadium(IV). At pH approximately 1.5, vanadium(IV) forms a 1:1 pale-violet complex with HMBPT in aqueous solution. An intense clear violet layer was formed after flotation, by adding an oleic acid (HOL) surfactant. The composition of the float was 1:1 [V(IV)]:[HMBPT]. A highly selective and sensitive spectrophotometric procedure was proposed for the determination of microamounts of V(IV) as its floated complex. The molar absorptivities of the V(IV)-HMBPT and V(IV)-HMBPT-HOL systems were 0.4 x 10(4) and 0.12 x 10(5) L mol(-1) cm(-1) at 560 nm, respectively. The formation constants of the species formed in the presence and absence of HOL were 4.6 x 10(7) and 8.7 x 10(5) L mol(-1), respectively. Beer's law was obeyed up to 1 x 10(-4) mol L(-1) in the aqueous layer as well as in the oleic acid layer. The HMBPT-V(IV) complexes formed in the aqueous solution and scum layer were characterized by elemental analysis, infrared and UV spectrophotometric studies. The mode of chelation between V(IV) and HMBPT is proposed to be due to a reaction between the protonated bidentate HMBPT ligand and V(IV) through the S=C and N=C groups. Interferences from various foreign ions were avoided by adding excess HMBPT and/or Na2S2O3 as a masking agent. The proposed flotation method was successfully applied to the analysis of V(IV) in synthetic mixtures, wastes of power stations, simulated samples and in real ores. The separation mechanism is discussed.

A vanadium-51 NMR study of the binding of vanadate and peroxovanadate to proteins.

51V quadrupolar central transition NMR spectra of buffered (pH 7.6-8.0) solutions of bovine apo-transferrin (Tf) and bovine prostatic acid phosphatase (Pp) treated with vanadate show normal features (chemical shifts between -515 and -542 ppm) corresponding to the complexation of VO2+ to the Tf binding site and the Pp active centre, respectively. Addition of H2O2 leads to the temporary formation of complexed VO(O2)+ (delta approximately -595). Vanadate-dependent bromoperoxidase from the alga Ascophyllum nodosum exhibits an unusually high shielding both for the native (delta = -931) and the peroxo form (delta = -1135) of the enzyme. A resonance at -471 ppm is traced back to an inactive form with oxovanadium(V) in a trigonal-bipyramidal array.

Variable heating rate thermogravimetric analysis as a mechanism to improve efficiency and resolution of the weight loss profiles of three model pharmaceuticals.

The effect of variable heating rates on the efficiency or resolution of the derivative of the thermogravimetry profiles of three model pharmaceutical compounds was investigated. The variable heating system utilized computer controlled algorithms for the evaluation of crystalline sodium warfarin, DuP 532 and hydrated DuP 925 as model compounds with one, two and three step weight loss profiles, respectively. As the heating modes were increased through each of the eight settings, the minimum heating rate decreased while the efficiency and resolution and the analysis times increased. The observed weight loss remained relatively constant for each of the model compounds as the heating modes were increased. The efficiency of the derivative of the weight loss profile of crystalline sodium warfarin increased from 121 to 621 as the heating mode increased. The resolution between the two steps of the derivative of the weight loss profile of DuP 532 increased from 1.73 to 3.88 as the heating mode increased. For hydrated DuP 925, the resolution increased from 1.49 to 5.46 between steps 1 and 2 of the derivative of the weight loss profile and from 1.87 to 3.24 between steps 2 and 3 of the derivative of the weight loss profile. Variable heating rates provided a valuable aid in obtaining high efficiency/resolution thermograms. The enhanced efficiency/resolution permitted greater separation of the volatilization process, especially for samples with multi-step weight loss profiles. Increasing the heating mode afforded higher efficiencies/resolutions that typically reached a maximum value at mode 6.

A novel dimeric oxovanadium (IV) species identified in Saccharomyces cerevisiae cells.

Saccharomyces cerevisiae cells stored oxovanadium (IV) ions in a dimeric form. In the late stationary phase Saccharomyces cerevisiae cells grown in rich medium containing concentrations of oxovanadium (V), orthovanadate from 12 to 18 mM, causing growth stasis, a dimeric oxovanadium (IV) species was identified by EPR spectroscopy. The EPR spectrum exhibited at 110 K the low-field forbidden deltaMs = +/-2 transition at g around 4 and the half-field deltaMs = +/-1 15-lines feature at g around 2 out of the presence of a triplet state by the coupling of the oxovanadium (IV) ions in a dimeric form. Hyperfine splitting of 75.2 x 10(-4) cm(-1) and an interionic distance of about 4.4 angstroms was calculated. The dimeric species was localized in the cellular cytoplasmic space.

Electron paramagnetic resonance studies and effects of vanadium in Saccharomyces cerevisiae.

Vanadium uptake by whole cells and isolated cell walls of the yeast Saccharomyces cerevisiae was studied. When orthovanadate was added to wild-type S. cerevisiae cells growing in rich medium, growth was inhibited as a function of the VO4(3-) concentration and the growth was completely arrested at a concentration of 20 mM of VO4(3-) in YEPD. Electron paramagnetic resonance (EPR) spectroscopy was used to obtain structural and dynamic information about the cell-associated paramagnetic vanadyl ion. The presence of EPR signals indicated that vanadate was reduced by whole cells to the vanadyl ion. On the contrary, no EPR signals were detected after interaction of vanadate with isolated cell walls. A 'mobile' and an 'immobile' species associated in cells with small chelates and with macromolecular sites, respectively, were identified. The value of rational correlation time tau r indicated the relative motional freedom at the macromolecular site. A strongly 'immobilized' vanadyl species bound to polar sites mainly through coulombic attractions was detected after interaction of VO2+ ions with isolated cell walls.

Physicochemical properties of the novel heteropolyanion antiviral hexapotassium-alpha-vanado-11-tungstoborate (DuP 925).

Hexapotassium-alpha-vanado-11-tungstoborate (DuP 925) is a yellow irregular-shaped crystalline powder. The DSC thermogram indicates that decomposition begins to occur above 250 degrees C. The compound exhibits a volatile loss of 3.7% by thermogravimetric analysis. The drug substance adsorbs water reaching a 7.1% volatile loss after 3 weeks at 85% relative humidity. The solubility of DuP 925 in water is high (1.6 g/ml at pH 4.8). Changes in pH have a negligible effect on the solubility with values of 1.3 g/ml in 0.1 N HCl and 1.4 g/ml in 0.1 N NaOH. The solubility is minimally affected by changes in sodium ion concentration. The compound ion pairs with tetrabutyl-ammonium ions at 1:2 and 1:6 ratios, with the 1:6 ion pair having an affinity over six orders of magnitude greater than that of the 1:2 ion pair. The degradation of DuP 925 in solution follows apparent first-order kinetics over the pH range of 0.6 to 12.6 at 80 degrees C. Citrate, EDTA, and phosphate buffers are catalytic at the pH minimum, with citrate and EDTA being stronger catalysts than phosphate. Acetate buffers appear to have negligible catalytic effects at pH 4 to 5. The degradation proceeds through the formation of the symmetrical dodecatungstoborate [BW12O40]-5. In acid, the dodecatungstoborate is stable, while in base it degrades further. Increasing the ionic strength has a catalytic effect on the degradation of DuP 925, while changes in the initial concentration of DuP 925 have a negligible effect on the stability. The pH-rate profile indicates a pH minimum of approximately 3.

The lymphotoxic action of vanadate.

The acute toxicity of ammonium metavanadate (15.5 mg/kg) in mice was investigated to examine the induction of lymphoid necrosis to (1) verify the reproducibility of the lesions in the thymus, lymph nodes, and spleen; (2) determine whether the necrosis of lymphoid tissue previously observed during the first 3 days post-treatment but absent at 14 days was the result of differences in sensitivity of the mice or the result of recovery from the effects of vanadium; and (3) determine whether differences in the presence and the degree of necrosis between thymus and spleen were correlated with differences in the uptake of vanadium in these tissues. A timed sacrificed study was conducted in conjunction with a 48V tracer. In this study, BALB/C mice were injected subcutaneously (s.c.) with ammonium metavanadate solution (15.5 mg/kg). Groups of mice were sacrificed at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 14, 21, and 28 days postexposure. Lymphoid necrosis was found in the thymus, spleen, lymph nodes, and bone marrow, with the necrosis being most severe in the thymus. The necrosis was moderate at 0.5 days, most severe at 2 to 3 days, with recovery beginning at 4 days, and proceeding to full recovery at 14 to 28 days. At 0.5 days post-treatment, the concentration of vanadium in thymus and spleen was 4.4 and 8.3 micrograms/g, respectively. At all post-treatment periods, with the exception of the 1- and the 4-day periods, the concentration of vanadium in spleen was significantly higher than in the thymus, p less than 0.05. The treated animals showed neurological signs (ataxia, convulsion, dyspnea, and paralysis of hind legs) between 5 min and 54 hr post-treatment, but the concentration of vanadium in the brain was very low during this period (less than 5.2% of blood concentration).

Evidence for the existence of two equilibrium conformations of the ternary complex of myosin subfragment-1, ADP, and orthovanadate.

In order to investigate the flexibility of the ternary complex consisting of myosin subfragment-1 (S1), ADP, and orthovanadate (Vi), i.e., S1.ADP.Vi, the exchangeability of the bound ADP was examined. After isolation of the ternary complex of S1.ADP.Vi by gel filtration, 3'-O-(N-methylanthraniloyl)-ADP (Mant-ADP), a fluorescent analogue of ADP, was added at 0.5 degrees C. The added Mant-ADP was incorporated into the ternary complex very slowly by replacing the bound ADP. The nucleotide exchange occurred without regeneration of the ATPase activity of S1. Similarly, the ternary complex of S1.Mant-ADP.Vi prepared and isolated by gel filtration according to Hiratsuka (3, 4), was incubated with ADP (2.4 mM) at 4.5 degrees C. The nucleotide exchange of S1.Mant-ADP.Vi with ADP occurred in two phases with the apparent rates of 4.5 x 10(-4) s-1 (the fast phase) and 6.7 x 10(-6) s-1 (the slow phase). Biphasic exchange of the bound nucleotide was also observed with S1(A1) isozyme, indicating that the biphasic exchange did not correspond to two S1 isozymes. The apparent rates of the fast and the slow phases increased with the concentration of the added ADP, but they became saturated at an ADP concentration of the order of 2 mM, indicating that the nucleotide exchange reaction involves a step (or steps) which is insensitive to the concentration of free ADP in the solution. This step might be a reversible isomerization.