Cumulative Title Index

Abstract

Quantitative data on the speciation of chitosan (310 kDa) with low and high molecular weight carboxylates in aqueous solution are reported. The following carboxylic ligands were considered: monocarboxylate (butyrate); dicarboxylates (malonate, succinate, azelate); tricarboxylate (1,2,3-propa-netricarboxylate); tetracarboxylate (1,2,3,4-butanetetracarboxylate); polyacrylates (2.0 and 20 kDa); polymethacrylate (5.4 kDa). The investigation was performed by potentiometry at t =25°C, at low ionic strength (without addition of supporting electrolyte) and at I =0.15mol L^?1 (NaCl). For all the systems the formation of (chitosan)LH_i species was found (L = carboxylic ligand; i = 1 to 4 depending on the carboxylic ligand considered). The stability of proton–chitosan–carboxylate species depends on the number of carboxylic groups involved in the complexation, and it was possible to calculate a rough free energy value per bond ΔG_n = ?15±2kJ mol^?1. By using the stability data, the quantitative sequestering capacity of chitosan towards the carboxylates here considered [expressed as the-log(total chitosan concentration) necessary to bind 50% of carboxylate, i.e., pL₅₀] was calculated for different pH values, at low ionic strength and at I =0.15 mol L^?1. The pL₅₀ values, ranging from 3 to 7, show that chitosan is quite a strong sequestering agent towards carboxylates. Evidences were also obtained for the different behaviour between low and high molecular weight carboxylates.     

An assessment of thermodynamic reaction constants for simulating aqueous environmental monomethylmercury speciation

ABSTRACT

Monomethylmercury (CH₃Hg ⁺) is both the most ecologically significant and the least well characterized species of mercury in environmental settings. Our understanding of the environmental speciation behavior of this compound is limited both as the result of lesser available laboratory data (when compared to inorganic mercury) as well as the uncertainties associated with our understanding of the properties of environmental ligands. A careful examination and synthesis of data reported in the technical literature led to the following findings: (1) a 25°C, zero ionic strength bicarbonate ion complexation constant estimate is remarkably close to an earlier reported value at 0.4 M: CH₃Hg⁺ + HCo₃^-?CH₃HgHCO₃,log₁₀K = 2.6 (±0.22, 1 SD), (2) three 25°C zero ionic strength reaction constants reported by DeRobertis et al.(1998) were confirmed to within ~±0.1 log₁₀K units: CH₃Hg ⁺+ OH^-?CH₃HgOH, log₁₀K = 9.47; 2CH₃Hg ⁺ + H₂O?(CH₃Hg)₂OH ⁺ + H⁺, log₁₀K =?2.15; CH₃Hg ⁺+ Cl^-?CH₃HgCl, log₁₀K = 5.45, (3) “best estimate” literature complexation constants corrected to zero ionic strength include: CH₃Hg ⁺ + F^-?CH₃HgF, log₁₀K = 1.75 (20°C corr. Schwart-zenbach and Schellenberg, 1965); CH₃Hg ⁺ + Br^-?CH₃HgBr, log₁₀K = 6.87 (20°C corr. Schwartzenbach and Schellenberg, 1965); CH₃Hg ⁺ +1^-?CH₃HgI, log₁₀K = 8.85 (20°C corr. Schwartzenbach and Schellenberg, 1965); and CH₃Hg ⁺+ SO₄^2-?CH₃HgSO₄^-,log₁₀K = 2.64 (25°C, DeRobertis et al., 1998), (4) literature reported values for simulating monomethylmercury complexation with the carbonate ion may be too low: CH₃Hg ⁺+ CO₃^2-?CH₃HgCO₃^-, log₁₀K = 6.1 (Rabenstein et al., 1976; Erni, 1981), and (5) ‘‘best estimate’’ constants for simulating methyl mercury complexation with reduced environmental sulfur species include: CH₃Hg ⁺ + S^2-?CH₃HgS ^-, log₁₀K = 21.1; CH³Hg ⁺+ SH ^-? CH3HgSH, log₁₀K = 14.5 (H ⁺ + SH^-?CH₂S, log₁₀K = 6.88; Dyrssen and Wedborg, 1991); CH₃Hg ⁺ + RS^-?CH₃HgSR, log₁₀K = 16.5 (H + + RS^-?RSH, log₁₀K = 9.96; Qian et al., 2002); and CH₃Hg ⁺+ CH₃HgS^{1 -}?(CH₃Hg)₂S, log₁₀K = 16.32 (Schwartzenbach and Schellenberg, 1965; Rabenstein et al., 1978; and Erni, 1981).     

Development of a transgenic tobacco plant for phytoremediation of methylmercury pollution

To develop the potential of plant for phytoremediation of methylmercury pollution, a genetically engineered tobacco plant that coexpresses organomercurial lyase (MerB) with the ppk-specified polyphosphate (polyP) and merT-encoding mercury transporter was constructed by integrating a bacterial merB gene into ppk/merT-transgenic tobacco. A large number of independent transgenic tobaccos was obtained, in some of which the merB gene was stably integrated in the plant genome and substantially translated to the expected MerB enzyme in the transgenic tobacco. The ppk/merT/merB-transgenic tobacco callus showed more resistance to methylmercury (CH₃Hg⁺) and accumulated more mercury from CH₃Hg⁺-containing medium than the ppk/merT-transgenic and wild-type progenitors. These results suggest that the MerB enzyme encoded by merB degraded the incorporated CH₃Hg⁺ to Hg²⁺, which then accumulated as a less toxic Hg-polyP complex in the tobacco cells. Phytoremediation of CH₃Hg⁺ and Hg²⁺ in the environment with this engineered ppk/merT/merB-transgenic plant, which prevents the release mercury vapor (Hg⁰) into the atmosphere in addition to generating potentially recyclable mercury-rich plant residues, is believed to be more acceptable to the public than other competing technologies, including phytovolatilization.     

Mercury's neurotoxicity is characterized by its disruption of selenium biochemistry

Background

Methylmercury (CH₃Hg⁺) toxicity is characterized by challenging conundrums: 1) “selenium (Se)-protective” effects, 2) undefined biochemical mechanism/s of toxicity, 3) brain-specific oxidative damage, 4) fetal vulnerability, and 5) its latency effect. The “protective effects of Se” against CH₃Hg⁺ toxicity were first recognized >50?years ago, but awareness of Se's vital functions in the brain has transformed understanding of CH₃Hg⁺ biochemical mechanisms. Mercury's affinity for Se is ~1 million times greater than its affinity for sulfur, revealing it as the primary target of CH₃Hg⁺ toxicity.

The chemistry and transport of mercury in a small wetland in the Adirondack region of New York, USA

The biogeochemistry of Hg was evaluated in a small wetland in the Adirondack region of New York. Concentrations of total Hg (Hg_T) in streamwater draining the wetland showed little temporal variation. The annual areal watershed flux of Hg_T (2.2 µg/m²-yr) was considerably smaller than regional inputs of atmospheric deposition of Hg_T, indicating that the terrestrial environment is a net sink for atmospheric deposition of Hg_T. Drainage inputs of Hg_T were conservatively transported through the beaver impoundment. The annual flux of total methyl mercury (CH₃Hg⁺ _T was greater than literature values of atmospheric deposition suggesting that the watershed is a net source of CH₃Hg⁺ _T . Stream concentrations of CH₃Hg⁺ _T increased during low-flow summer conditions in a riparian wetland, and particularly at the outlet of the beaver impoundment. Net production of CH₃Hg⁺ _T occurred in the beaver impoundment (0.45 µg/m²-yr). Rates of net methylation for the beaver impoundment were comparable to values reported in the literature for wetlands.     

Biosorption of inorganic and methyl mercury by a biosorbent from Aspergillus niger

A biosorbent prepared by alkaline extraction of Aspergillus niger biomass was evaluated for its potential to remove mercury species – inorganic (Hg²⁺) and methyl mercury (CH₃Hg⁺) – from aqueous solutions. Batch experiments were carried out to determine the pH and time profile of sorption for both species in the pH range 2–7. The Hg²⁺ exhibited more rapid sorption and higher capacity than the CH₃Hg⁺. Further, removal of both mercury species from spiked ground water samples was efficient and not influenced by other ions. Sorption studies with esterified biosorbent indicated loss of binding of both mercury species (>80%), which was regained when the ester groups were removed by alkaline hydrolysis, suggesting the involvement of carboxyl groups in binding. Further, no interconversion of sorbed species occurred on the biomass. The biosorbent was reusable up to six cycles without serious loss of binding capacity. Our results suggest that the biosorbent from Aspergillus niger can be used for removal of mercury and methyl mercury ions from polluted aqueous effluents.     

Interactions between selenium and methylmercury in rat brain

The interaction of selenium with methylmercury was investigated in brain of animals labeled with ⁷⁵SeO₃^2? and CH₃²⁰³Hg⁺. Brains were fractionated into subcellular components and the cytosol was further fractionated by chromatography on Sephadex G-150 and G-200. The main result of these studies was evidence suggesting a shift of ⁷⁵Se from the cytosol to the mitochondrial fraction in brain when CH₃Hg⁺ was given. Concurrent equimolar (10 μmoles/kg) selenite injections increased the uptake of Hg but did not alter ²⁰³Hg distribution in brain. Changing the dose of CH₃Hg⁺ from 1 to 38 μmoles/kg had little effect on Hg uptake (% of dose per g). Gel filtrations on Sephadex G-150 and G-200 revealed that ²⁰³Hg in cytosol followed a pattern more closely related to protein (A₂₈₀) than to ⁷⁵Se, although a considerable portion of both isotopes eluted with proteins in the void volume. Assays of whole brain homogenates revealed a slight reduction in glutathione peroxidase activity in CH₃Hg⁺-treated rats which was not seen when equimolar selenite was injected with the CH₃Hg⁺.     

Dissolved and suspended mercury. species in the Wabigoon River (Ontario,Canada): seasonal and regional variations

Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario. Concentrations and loadings of particulate methyl mercury (CH₃Hg⁺) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH₃Hg⁺, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of desorption from sediments due to elevated concentrations of Cl⁻ ions. Loadings of dissolved CH₃Hg⁺ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major spring-flood episode in May. During July–August dissolved CH₃Hg⁺ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved and suspended CH₃Hg⁺ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved Hg was a function of dissolved Cl⁻. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular weight humic and humic-Fe components), and selenium (Se); but CH₃Hg⁺ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between CH₃Hg⁺ and Hg²⁺ ions. CH₃Hg⁺ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer. Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms. Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl₂, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis. Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH₃Hg⁺ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H₂O₂, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable Hg (in September). Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden to silt-clay mud further downstream. Hg in silt-clay mud relatively far (> 35 km) downstream from the source of pollution or in unpolluted areas appeared to be more readily solubilized by Cl⁻ ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH₃Hg⁺ levels and CH₃Hg⁺/total Hg ratios), and was to a greater degree organically bound (H₂O₂-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient scavengers of CH₃Hg⁺. The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended load and by sedimentation and treatment with Hg-binding agents in special receiving basins.     

Silver nanoclusters stabilized with denatured fish sperm DNA and the application on trace mercury ions detection

In this study, fluorescent silver nanoclusters (Ag NCs) were synthesized using denatured fish sperm DNA as the template. In contrast to other methods, this method did not use artificial DNA as the template. After their reaction with denatured fish sperm DNA, Ag⁺ ions were reduced by NaBH₄ to form Ag NCs. The Ag NCs showed a strong fluorescence emission at 650 nm when excited at 585 nm. The fluorescence intensity increased fourfold at pH 3.78, controlled with Britton–Robinson buffer solution. The fluorescence of the Ag NCs was quenched in the presence of trace mercury ions (Hg²⁺) in a weakly acidic medium and nitrogen atmosphere. The extent of the fluorescence quenching of Ag NCs strongly depends on the Hg²⁺ ion concentration over a linear range from 2.0 nmol L^?1 to 3.0 μmol L^?1. The detection limit (3σ/k) for Hg²⁺ was 0.7 nmol L^?1. Thus, a sensitive and rapid method was developed for the detection of Hg²⁺ ions.     

褐纹报春苣苔组织培养与快速繁殖

褐纹报春苣苔(Primulina glandaceistriata)是一种极具观赏价值的喀斯特地区野生花卉,目前尚未有褐纹报春苣苔组培快繁的研究报道。该研究以褐纹报春苣苔的叶片为外植体,通过两种途径建立其组培快繁体系。结果表明:适宜的不定芽诱导培养基为MS+6-BA 2.0 mg·L~(-1)+NAA 0.10 mg·L~(-1),适宜的不定芽增殖培养基为MS+ZT 2.0 mg·L~(-1)+NAA 0.10 mg·L~(-1)+活性炭0.05 g·L~(-1),增殖系数为11.09;适宜的愈伤组织诱导培养基为MS+TDZ 2.0 mg·L~(-1)+NAA 0.10 mg·L~(-1),适宜的愈伤组织分化培养基为MS+ZT 1.0 mg·L~(-1)+NAA 0.10mg·L~(-1),分化系数为12.46;适宜的生根培养基为1/2MS+IBA 0.1 mg·L~(-1)+活性炭0.05 g·L~(-1)或1/2MS+IBA0.5 mg·L~(-1)+活性炭0.05 g·L~(-1),生根率为100%。该研究结果成功建立了褐纹报春苣苔的组培快繁体系,为今后褐纹报春苣苔的种苗繁殖和遗传转化提供了技术支持。     

Phenoxyl-copper(II) complexes: models for the active site of galactose oxidase

 The reaction of the macrocycles 1,4,7-tris (3,5-di-tert-butyl-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L¹H₃, or 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L²H₃, with Cu(ClO₄)₂·6H₂O in methanol (in the presence of Et₃N) affords the green complexes [Cu^II(L¹H)] (1), [Cu^II(L²H)]·CH₃OH (2) and (in the presence of HClO₄) [Cu^II(L¹H₂)](ClO₄) (3) and [Cu^II(L²H₂)] (ClO₄) (4). The Cu^II ions in these complexes are five-coordinate (square-base pyramidal), and each contains a dangling, uncoordinated pendent arm (phenol). Complexes 1 and 2 contain two equatorially coordinated phenolato ligands, whereas in 3 and 4 one of these is protonated, affording a coordinated phenol. Electrochemically, these complexes can be oxidized by one electron, generating the phenoxyl-copper(II) species [Cu^II(L¹H)]^+ ·, [Cu(L²H)]^+ ·, [Cu^II(L¹H₂)]^2+ ·, and [Cu^II(L²H₂)]^2+ ·, all of which are EPR-silent. These species are excellent models for the active form of the enzyme galactose oxidase (GO). Their spectroscopic features (UV-VIS, resonance Raman) are very similar to those reported for GO and unambiguously show that the complexes are phenoxyl-copper(II) rather than phenolato-copper(III) species. Received: 10 February 1997 / Accepted: 7 April 1997     

Evaluation of Lupinus Species to Accumulate Heavy Metals From W aste Waters

Several Lupinus species, for example, Lupinus albus, Lupinus luteus, Lupinus angustifolius, and Lupinus hispanicus were used to accumulate Mn(II), Cd(II), Pb(II), Cr(III), Cr(VI), Hg²⁺, and CH₃Hg⁺ from waste waters. The influence of different species concentrations (50 and 100 mg L^-1) and pH on growing behavior as well as the resulting distribution of metals in the plants were investigated. The results obtained showed that lupins were able to germinate and to grow in the presence of the metals mentioned above, even when they were present at levels as high as 50 mg L^-1. Accumulation of Pb(II), Cr(III), and Cd(II) was higher in roots than in shoots. As far as mercury is concerned, the highest CH₃Hg and Hg²⁺ accumulation was detected in roots, but fast transport toward the leaves was noticed. In contrast to mercury, the uptake of chromium seems to be influenced by the chemical form of the analyte, remaining Cr(VI) in solution. No differences in growing behavior and accumulation were observed for the four Lupinus species studied. Even though plants were exposed only a relatively short time to the metal solutions, metal concentrations of approximately 2 g/kg of dry matter were detected in the young lupins plants. The feasibility of utilizing Lupinus plants for the removal of heavy metals from wastewater was also investigated. Lupins were able to grow under extreme conditions (wastewater, pH lower than 2) and to remove 98% of the initial amount of toxic metals present in the sample.     

Biosorption of Malathion by immobilized cells of Bacillus sp. S14

Abstract

Biosorption is potentially an attractive technology for the treatment of wastewater by removing pesticide molecules from dilute solutions. This study investigated the feasibility of an isolated Bacillus sp. S₁₄ immobilized in calcium alginate that was used as a biosorbent for Malathion removal from aqueous solutions in batch mode. The highest value of Malathion uptake by isolated Bacillus sp. S14 (1.33g L^?1, dry basis) immobilized in 3% calcium alginate was 64.4% at 25°C and pH7.0 when the initial Malathion concentration was 50 mg L^?1. Equilibrium was attained at 8h. The sorption data conformed well to the Fruendlich isotherm model.     

The human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) is irreversibly inhibited by inorganic (Hg) and organic mercury (CH3Hg): Mechanism and kinetics

Human arylamine N-acetyltransferase 1 (NAT1) is a xenobiotic-metabolizing enzyme that biotransforms aromatic amine chemicals. We show here that biologically-relevant concentrations of inorganic (Hg²⁺) and organic (CH₃Hg⁺) mercury inhibit the biotransformation functions of NAT1. Both compounds react irreversibly with the active-site cysteine of NAT1 (half-maximal inhibitory concentration (IC₅₀) = 250 nM and k_inact = 1.4 × 10⁴ M⁻¹ s⁻¹ for Hg²⁺ and IC₅₀ = 1.4 μM and k_inact = 2 × 10² M⁻¹ s⁻¹ for CH₃Hg⁺). Exposure of lung epithelial cells led to the inhibition of cellular NAT1 (IC₅₀ = 3 and 20 μM for Hg²⁺ and CH₃Hg⁺, respectively). Our data suggest that exposure to mercury may affect the biotransformation of aromatic amines by NAT1.     

Optimization of some parameters influencingThermoascus aurantiacus growth: Effects of lignin-related compounds

Statistical designs were used to optimize some parameters affecting the growth rate of a Brazilian strain ofThermoascus aurantiacus. The mycelial growth rate was measured using the horizontal tube method. Temperature of incubation and initial pH were the major factors affecting the growth rate. They were optimal at 6.0 and 48°C, respectively. The maximum growth rate was obtained in solid Czapek modified medium containing 1.5% glucose and 38.4 mEq L^–1NaNO₃. Under these conditions, the growth rate ofT. aurantiacus was 5.16±0.10 mm h^–1. Lignin-related compounds such as tannins and extractive substances added at 0.1% (w/v) to the minimal Czapek medium increased growth rate 14% and 29%, respectively.     

Probing the coordination behavior of Hg2+, CH3Hg+, and Cd2+ towards mixtures of two biological thiols by HPLC-ICP-AES

Hepatocyte cytosol contains a multitude of proteins, but also comparatively high concentrations of l-glutathione (GSH, ~ 5.0 mM) and l-cysteine (Cys, ~ 0.5 mM). Since Hg²⁺, CH₃Hg⁺ and Cd²⁺ have a high affinity for thiols, their coordination to these thiols is likely involved in their intracellular transport. The comparative coordination behavior of these metal species towards mixtures of Cys and GSH, however, has not been studied under near physiological conditions. To probe these toxicologically relevant interactions, each metal species was separately injected onto a C₁₈-HPLC column (37 °C) that had been equilibrated with phosphate buffered saline (PBS) that contained 5.0 mM GSH (mobile phase) and detected with an inductively coupled plasma atomic emission spectrometer. The incremental increase of the Cys concentration in the mobile phase (in 0.5 or 1.0 mM steps) up to 10 mM followed by the chromatography of each metal species decreased the retention of Hg²⁺ and CH₃Hg⁺ albeit in a different manner. This behavior was rationalized in terms of the replacement of hydrophobic GS-moieties coordinated to each mercurial by less hydrophobic Cys-moieties. In contrast, a Cd-peak eluted close to the void volume with all investigated mobile phases. Using X-ray absorption spectroscopy, the Cd-compound that eluted with a PBS-buffer that contained 5.0 mM GSH was structurally characterized as tetrahedral (GS)₄Cd. Thus, the in vivo formation of (GS)₄Cd must be considered and HPLC-ICP-AES is identified as a useful tool to probe dynamic bioinorganic processes which involve the interaction of a metal ion with multiple ligands under physiologically relevant conditions.     

Hg2+-induced leakage of electrolytes and inhibition of NO3 − utilization inNostoc calcicola

Summary The effect of mercury (Hg²⁺) in the absence and presence of methylmercury (CH₃Hg⁺), cadmium (Cd²⁺), copper (Cu²⁺), nickel (Ni²⁺) and calcium (Ca²⁺) on Nostoc calcicola Bréb. has been studied in terms of electrolyte leakage, NO₃ ^– uptake and in vivo nitrate reductase (NR) activity to discover any possible correlation among such parameters under Hg²⁺ stress. Leakage of electrolytes from Hg²⁺-treated cyanobacterial cells was directly proportional to Hg²⁺ concentrations and exposure time. In comparison to NO₃ ^– uptake, an about 60-fold slower rate of NR activity was observed in the untreated cultures, the former being five times more Hg²⁺-sensitive. A non-competitive synergistic interaction of Hg²⁺ with CH₃Hg⁺ or Cd²⁺ and antagonistic with that of Ni²⁺ or Ca²⁺ has been observed for both the processes of NO₃ ^– utilization. The antagonistic interaction of Cu²⁺ with Hg²⁺ in terms of NO₃ ^– uptake and synergistic with respect to NR activity, has been attributed to the dual bonding preference of Cu²⁺ for cellular ligands. These findings suggest that (a) a statistically significant correlation exists among such parameters; (b) Hg²⁺ predominantly attacks the cyanobacterial cell membrane; (c) Hg²⁺ inhibits NO₃ ^– utilization; (d) the presence of other cations increases or decreases the inhibitory actions of Hg²⁺.     

Skeletal muscle glycogen phosphorylase is irreversibly inhibited by mercury: Molecular,cellular and kinetic aspects

Muscle glycogen phosphorylase (GP) plays an important role in muscle functions. Mercury has toxic effects in skeletal muscle leading to muscle weakness or cramps. However, the mechanisms underlying these toxic effects are poorly understood. We report that GP is irreversibly inhibited by inorganic (Hg²⁺) and organic (CH₃Hg⁺) mercury (IC₅₀ = 380 nM and k_inact = 600 M⁻¹ s⁻¹ for Hg²⁺ and IC₅₀ = 43 μM and k_inact = 13 M⁻¹ s⁻¹ for CH₃Hg⁺) through reaction of these compounds with cysteine residues of the enzyme. Our data suggest that the irreversible inhibition of GP could represent one of the mechanisms that contribute to mercury-dependent muscle toxicity.     

Speciation of dimethyltin(IV) – and trimethyltin(IV) – carbocysteinate and – glutamate systems in aqueous media

Abstract

The formation of complex species in the dimethyltin(IV) and trimethyltin(IV)-carboxymethyl-L-cysteinate (carbocysteinate) systems in NaCl_aq, at different ionic strengths, and in a multicomponent Na⁺, K⁺, Ca²⁺ ,Mg²⁺, Cl^? and SO₄^2-? medium representative of the seawater major composition, is discussed. Experimental results give evidence for the formation of the following species (L = carbocysteinate): [(CH₃)₂Sn(L)]⁰, [(CH₃)₂Sn(HL)]⁺, [(CH₃)₂Sn(OH)(L)]^?, [(CH₃)₂Sn(OH)₂(L)]^2? in the DMT–CCYS system, and [(CH₃)₃Sn(HL)]⁰, [(CH₃)₃Sn(L)]^? and [(CH₃)₃Sn(OH)(L)]^2? in the TMT-CCYS system. The ionic strength dependence of formation constants was taken into account by an extended Debye Hückel type equation and by the SIT (Specific ion Interaction Theory). Measurements were carried out also on the dimethyltin(IV)-glutamate and trimethyltin(IV)-glutamate systems in NaCl_aq, owing the strict similarity of glutamate and carbocysteinate. Results obtained show the formation of complex species having the same stoichiometry as those formed in the DMT- and TMT-carbocysteinate systems, with very similar stability, confirming that carbocysteinate behaves as a dicarboxylic amino acid without involving the sulfur-bridge potential binding site in metal coordination.     

Inhibition studies of soybean (Glycine max) urease with heavy metals,sodium salts of mineral acids,boric acid,and boronic acids

Various inhibitors were tested for their inhibitory effects on soybean urease. The K_i values for boric acid, 4-bromophenylboronic acid, butylboronic acid, and phenylboronic acid were 0.20?±?0.05?mM, 0.22?±?0.04?mM, 1.50?±?0.10?mM, and 2.00?±?0.11?mM, respectively. The inhibition was competitive type with boric acid and boronic acids. Heavy metal ions including Ag⁺, Hg²⁺, and Cu²⁺ showed strong inhibition on soybean urease, with the silver ion being a potent inhibitor (IC₅₀ = 2.3?×?10^?8 mM). Time-dependent inhibition studies exhibited biphasic kinetics with all heavy metal ions. Furthermore, inhibition studies with sodium salts of mineral acids (NaF, NaCl, NaNO₃, and Na₂SO₄) showed that only F^? inhibited soybean urease significantly (IC₅₀ = 2.9?mM). Competitive type of inhibition was observed for this anion with a K_i value of 1.30?mM.