Removal of Cd2+, Pb2+, and Zn2+ from contaminated water using dolomite powder

Dolomite collected from Surat Thani Province in Thailand was investigated for use as a sorbent for the removal of divalent heavy metal cations from an aqueous solution. The sorbent had a surface area of 2.46 m²/g and a pH of zero point charge (pHzpc) of 9.2. Batch sorption was used to examine the effect of the pH (pH 3–7) on the sorption capacity of Cd²⁺, Pb²⁺ and Zn²⁺, alone or together as an equimolar mixture at various concentrations. Alone, each heavy metal cation was adsorbed faster at a higher pH, where the sorption of Cd²⁺ and Pb²⁺ fitted a Langmuir isotherm, but Zn²⁺ sorption best fitted a Freundlich isotherm. Under equimolar competitive sorption, the sorption capacity of each cation was decreased by 75.8% (0.29–0.07 mM/g), 82.8% (0.53–0.09 mM/g), and 95.7% (0.84–0.04 mM/g) for Cd²⁺, Pb²⁺ and Zn²⁺, respectively, compared to that with the respective single cation. Desorption of these heavy metal cations from dolomite was low, with an average desorption level of 0.06–17.4%. Furthermore, since dolomite is readily available and rather cheap, it is potentially suitable for use as an efficient sorbent to sorb Cd²⁺ and Pb²⁺, and perhaps Zn²⁺, from contaminated water.     

Effects of Cadmium, Lead, Mercury and Zinc on °-Aminolevulinic Acid Dehydratase Activity from Radish Leaves

The purpose of the present study was to investigate the in vitro and the in vivo effects of cadmium, zinc, mercury and lead on -aminolevulinic acid dehydratase (ALA-D) activity from radish leaves. The in vivo effect of these metals on growth, DNA and protein content was also evaluated. The results demonstrated that among the elements studied Cd²⁺ presented the highest toxicity for radish. 50% inhibition of ALA-D activity (IC₅₀) in vitro was at 0.39, 2.39, 2.29, and 1.38 mM Cd²⁺, Zn²⁺, Hg²⁺ and Pb²⁺, respectively. After in vivo exposure Cd²⁺, Zn²⁺, Hg²⁺ and Pb²⁺ inhibited ALA-D by about 40, 26, 34 and 15%, respectively. Growth was inhibited by about 40, 10, 25, and 5% by Cd²⁺, Zn²⁺, Hg²⁺, and Pb²⁺, respectively. DNA content was reduced about 35, 30, 20, and 10% for Cd²⁺, Zn²⁺, Hg²⁺, and Pb²⁺, respectively. The metal concentration in radish leaves exposed to Cd²⁺, Zn²⁺, Hg²⁺, and Pb²⁺ was 18, 13, 6, and 7 mol g^–1, respectively. The marked ability of radish to accumulate Cd²⁺ and Zn²⁺ raises the possibility of using this vegetable as a biomonitor of environmental contamination by these metals.     

Development of a fluorescent transgenic zebrafish biosensor for sensing aquatic heavy metal pollution

We report a transgenic zebrafish (Danio rerio) designed to respond to heavy metals using a metal-responsive promoter linked to a fluorescent reporter gene (DsRed2). The metallothionein MT-Ia1 promoter containing metal-responsive elements was derived from the Asian green mussel, Perna viridis. The promoter is known to be induced by a broad spectrum of heavy metals. The promoter-reporter cassette cloned into the Tol2 transposon vector was microinjected into zebrafish embryos that were then reared to maturity. A transgene integration rate of 28 % was observed. The confirmed transgenics were mated with wild-type counterparts, and pools of F₁ embryos were exposed to sub-lethal doses of Cd²⁺, Cu²⁺, Hg²⁺, Pb²⁺ and Zn²⁺. The red fluorescence response of zebrafish embryos was observed 8 h post- exposure to these sub-lethal doses of heavy metals using a fluorescence microscope. Reporter expression estimated by real-time PCR revealed eightfold, sixfold and twofold increase on exposure to highest concentrations of Hg²⁺, Cd²⁺ and Cu²⁺, while Pb²⁺ and Zn²⁺ had no effect. This biosensor could be a first-level screening method for confirming aquatic heavy metal bio-toxicity to eukaryotes.     

Biosorption of Cd, Cu, Pb, and Zn from aqueous solutions by the fruiting bodies of jelly fungi (Tremella fuciformis and Auricularia polytricha)

In this study, dried and humid fruiting bodies of Tremella fuciformis and Auricularia polytricha were examined as cost-effective biosorbents in treatment of heavy metals (Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺) in aqueous solution. The humid T. fuciformis showed the highest capacity to adsorb the four metals in the multi-metal solutions. The Pb²⁺ adsorption rates were 85.5%, 97.8%, 84.8%, and 91.0% by dried T. fuciformis, humid T. fuciformis, dried A. polytricha, and humid A. polytricha, respectively. The adsorption amount of Pb²⁺ by dried and humid T. fuciformis in Cd²⁺ + Pb²⁺, Cu²⁺ + Pb²⁺, Pb²⁺ + Zn²⁺, Cd²⁺ + Cu²⁺ + Pb²⁺, and Cd²⁺ + Zn²⁺ + Pb²⁺ solutions were not lower than that in Pb²⁺ solutions. The results suggested that in humid T. fuciformis, Cd²⁺, Cu²⁺, and Zn²⁺ promoted the Pb²⁺ adsorption by the biomass. In the multi-metal solutions of Cd²⁺ + Cu²⁺ + Pb²⁺ + Zn²⁺, the adsorption amount and rates of the metals by all the test biosorbents were in the order of Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺. Compared with the pseudo first-order model, the pseudo second-order model described the adsorption kinetics much better, indicating a two-step biosorption process. The present study confirmed that fruiting bodies of the jelly fungi should be useful for the treatment of wastewater containing Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺.     

Purification of glucose‐6‐phosphate dehydrogenase from rat (Rattus norvegicus) erythrocytes and inhibition effects of some metal ions on enzyme activity

Glucose‐6‐phosphate dehydrogenase (G6PD) is the first enzyme on which the pentose phosphate pathway was checked. In this study, purification of a G6PD enzyme was carried out by using rat erythrocytes with a specific activity of 13.7 EU/mg and a yield of 67.7 and 155.6‐fold by using 2′,5′‐ADP Sepharose‐4B affinity column chromatography. For the purpose of identifying the purity of enzyme and molecular mass of the subunit, a sodium dodecyl sulfate‐polyacrylamide gel electrophoresis was carried out. The molecular mass of subunit was calculated 56.5 kDa approximately. Then, an investigation was carried out regarding the inhibitory effects caused by various metal ions (Fe²⁺, Pb²⁺, Cd²⁺, Ag⁺, and Zn²⁺) on G6PD enzyme activities, as per Beutler method at 340 nm under in vitro conditions. Lineweaver–Burk diagrams were used for estimation of the IC₅₀ and K_i values for the metals. K_i values for Pb⁺², Cd⁺², Ag⁺, and Zn⁺² were 113.3, 215.2, 19.4, and 474.7 μM, respectively.     

Responses of elongation growth rate,turgor pressure and cell wall extensibility of stem cells of Impatiens balsamina to lead,cadmium and zinc

Elongation growth rate of stem cells of Impatiens balsamina was inhibited by the heavy metals Pb²⁺, Cd²⁺ and Zn²⁺ due to their suppression on cell wall extensibility. Effective turgor was also inhibited by Pb²⁺ and Cd²⁺ but it played a secondary role in reducing the stem cell elongation growth rate. The major rate-limiting factor for cell elongation growth was the cell wall extensibility. Furthermore, Cd²⁺ was found to be more toxic than Pb²⁺, while Pb²⁺ was more toxic than Zn²⁺.     

The metal-binding sites of the zinc-transporting P-type ATPase of Escherichia coli. Lys and Asp in the seventh and eighth transmembrane segments of ZntA contribute to the coupling of metal binding and ATPase activity

ZntA is a P-type ATPase which transports Zn²⁺, Pb²⁺ and Cd²⁺ out of the cell. Two cysteine-containing motifs, CAAC near the N-terminus and CPC in transmembrane helix 6, are involved in binding of the translocated metal. We have studied these motifs by mutating the cysteines to serines. The roles of two other possible metal-binding residues, K⁶⁹³ and D⁷¹⁴, in transmembrane helices 7 and 8, were also addressed. The mutation CAAC → SAAS reduces the ATPase activity by 50%. The SAAS mutant is phosphorylated with ATP almost as efficiently as the wild type. However, its phosphorylation with P_i is poorer than that of the wild type and its dephosphorylation rate is faster than that of the wild type ATPase. The CPC → SPS mutant is inactive but residual phosphorylation with ATP could still be observed. The most important findings of this work deal with the prospective metal-binding residues K⁶⁹³ and D⁷¹⁴: the substitution K693N eliminates the Zn²⁺-stimulated ATPase activity completely, although significant Zn²⁺-dependent phosphorylation by ATP remains. The K693N ATPase is hyperphosphorylated by P_i. ZntA carrying the change D714M has strong metal-independent ATPase activity and is very weakly phosphorylated both by ATP and P_i. In conclusion, K⁶⁹³ and D⁷¹⁴ are functionally essential and appear to contribute to the metal specificity of ZntA, most probably by being parts of the metal-binding site made up by the CPC motif.     

Lead inhibits 1,25-dihydroxyvitamin D-3 regulation of calcium metabolism in osteoblastic osteosarcoma cells (ROS 17/2.8)

We have determined the dose-response of 1,25-dihydroxyvitamin D-3 (1,25-(OH)₂D₃) on the intracellular free calcium-ion concentration ([Ca²⁺¹]_i) in the osteoblastic osteosarcoma cells, ROS 17/2.8, using ¹⁹F-NMR and the intracellular divalent cation indicator, 1,2-bis(2-amino-5-fluorephenoxy)ethane-N, N, N′, N′-tetraacetic acid (5F-BAPTA). The dose-response demonstrated an inverted U-shaped relationship with maximal elevation of [Ca²⁺]_i at doses of 1 to 10 nM 1,25-(OH)₂D₃. At 10 nM, 1,25-(OH)₂D₃ elevated the [Ca²⁺]_i from a control level of 118±4 nM to a peak value of 237±8 nM within 40 min. 1,25-(OH)₂D₃ also increased the intial rate of Ca²⁺ influx into ROs 17/2.8 cells, measured by ⁴⁵Ca uptake, with a dose-response relationship which paralleled its effects on [Ca²⁺]_i. Treatment of ROS 17/2.8 cells with Pb²⁺ at 1 and 5 μM significantly increased [Ca²⁺]_i but significantly reduced the 1,25-(OH)₂D₃-induced elevation of [Ca²⁺]i. Simultaneous treatment of naive cells with 1,25-(OH)₂D₃ and Pb²⁺ produce little reduction of 1,25-(OH)₂D₃ and Pb²⁺ produce little reduction of 1,25-(OH)₂D₃-induced ⁴⁵Ca uptake while 40 min treatment with Pb²⁺ before addition of 1,25-(OH)₂D₃ significantly reduced the 1,25-(OH)₂D₃-induced increase in ⁴⁵Ca influx. These findings suggest that Pb²⁺ acts by inhibiting 1,25-(OH)₂D₃-activation of Ca²⁺ channels and interferes with 1,25-(OH)₂D₃ regulation of Ca²⁺ metabolism in osteoblastic bone cells.     

Genes for all metals—a bacterial view of the Periodic Table

Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH₄ ⁺, K⁺, Mg²⁺, Co²⁺, Fe³⁺, Mn²⁺, Zn²⁺ and other trace cations, PO₄ ^3-, SO₄ ^2- and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids encode resistance systems for toxic metal and metalloid ions including Ag⁺ AsO₂ ^-, AsO₄ ^3-, Cd²⁺, Co²⁺, CrO₄ ²⁻, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, TeO₃ ²⁻, TI⁺ and Zn²⁺. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations. Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd²⁺-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with ³²P from [γ-³²P]ATP and drives ATP-dependent Cd²⁺ (and Zn²⁺) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson’s disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides, ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex functions as a chemiosmotic cation/protein exchanger to efflux Cd²⁺, Zn²⁺ and Co²⁺. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function together. Received 08 August 1997/ Accepted in revised form 01 November 1997     

Sorption of Heavy Metal Cations by Corn Mitochondria and the Effects on Electron and Energy Transfer Reactions

The passive sorption of Pb⁺², Cd⁺², Zn⁺², Co⁺², Ni⁺², and Mn⁺² by isolated corn mitochondria was determined, and, except for Pb⁺², the maximum sorption for each cation was about 58 nmol per milligram of protein. Sorption of Pb⁺² was apparently ten times greater, but precipitation may have been the cause of this larger value. The effects of Pb⁺², Cd⁺², Zn⁺², Co⁺², and Ni⁺² on acceptorless rates of electron transport for three substrates were determined. Greater than 50% inhibitions of oxidation were observed for succinate after additions of >0.1 mM Cd⁺², Zn⁺², or Pb⁺²: for NADH after additions of >0.5 mM Cd⁺² or Zn⁺²; and for malate + pyruvate after additions of >0.1 mM Cd⁺². Some inhibition of the rate of substrate oxidation was observed for most cations at higher concentrations. Coupling, as measured by ADP/O ratios, was inhibited at lowest concentrations by Cd⁺² or Zn⁺² and at higher concentrations by Co⁺² or Ni⁺². Substantial swelling of mitochondria oxidizing succinate was observed following additions of O.1 mM Cd⁺² or Pb⁺², Correlations are drawn between the effects of Pb⁺², Cd⁺², Zn⁺², Co⁺², and Ni⁺² and their sorption to mitochondrial membranes.     

The interaction of zinc, nickel and cadmium with serum albumin and histidine-rich glycoprotein assessed by equilibrium dialysis and immunoadsorbent chromatography

Human serum albumin (HSA) has been shown to bind 2–3 mol of Zn²⁺, Ni²⁺, or Cd²⁺ per mole of protein with apparent dissociation constants (K_d) in the range of 10 μm. Rabbit histidine-rich glycoprotein (HRG) binds 13, 9, and 6 mol of Zn²⁺, Ni²⁺, and Cd²⁺ per mole of protein, respectively, with apparent K_ds also near 10 μm. However, the binding of metals by HRG exhibits positive cooperativity, so that the apparent K_ds may underestimate HRGs true affinity for metal ions. The relative affinities of HSA and HRG for metal ions were found to be Zn²⁺ > Ni²⁺ > Cd²⁺. In addition, histidine (a serum metal chelator) affected the binding of Ni²⁺ by both proteins but not that of Zn²⁺ or Cd²⁺. At physiological concentrations of HSA (250 μm), HRG (2.5 μm), and histidine (100 μm), HRG bound 36% of the Zn²⁺, 9% of the Ni²⁺, and 13% of the Cd²⁺ at a total metal concentration of 25 μm. Under the same conditions HSA held 37% of the Zn²⁺, 14% of the Ni²⁺, and 56% of the Cd²⁺. Thus, HSA appears to have a lower intrinsic affinity for the three metals than HRG but would be expected to bind a higher proportion of these metals in serum. A specific immunoadsorbent column was prepared and used to study the metal binding by HRG in serum directly. Both ⁶⁵Zn²⁺ and ⁶³Ni²⁺ were associated with HRG in aliquots of rabbit serum after incubation with the corresponding metal ion. This evidence indicates that HRG must be considered as a metal binding component of serum.     

Physiologically Relevant Free Ca2+ Ion Concentrations Regulate STRA6-Calmodulin Complex Formation via the BP2 Region of STRA6

The interaction of calmodulin (CaM) with the receptor for retinol uptake, STRA6, involves an α-helix termed BP2 that is located on the intracellular side of this homodimeric transporter (Chen et al., 2016 [1]). In the absence of Ca²⁺, NMR data showed that a peptide derived from BP2 bound to the C-terminal lobe (C-lobe) of Mg²⁺-bound CaM (^MgCaM). Upon titration of Ca²⁺ into ^MgCaM-BP2, NMR chemical shift perturbations (CSPs) were observed for residues in the C-lobe, including those in the EF-hand Ca²⁺-binding domains, EF3 and EF4 (^CaK_D = 60 ± 7 nM). As higher concentrations of free Ca²⁺ were achieved, CSPs occurred for residues in the N-terminal lobe (N-lobe) including those in EF1 and EF2 (^CaK_D = 1000 ± 160 nM). Thermodynamic and kinetic Ca²⁺ binding studies showed that BP2 addition increased the Ca²⁺-binding affinity of CaM and slowed its Ca²⁺ dissociation rates (k_off) in both the C- and N-lobe EF-hand domains, respectively. These data are consistent with BP2 binding to the C-lobe of CaM at low free Ca²⁺ concentrations (<100 nM) like those found at resting intracellular levels. As free Ca²⁺ levels approach 1000 nM, which is typical inside a cell upon an intracellular Ca²⁺-signaling event, BP2 is shown here to interact with both the N- and C-lobes of Ca²⁺-loaded CaM (^CaCaM-BP2). Because this structural rearrangement observed for the ^CaCaM-BP2 complex occurs as intracellular free Ca²⁺ concentrations approach those typical of a Ca²⁺-signaling event (^CaK_D = 1000 ± 160 nM), this conformational change could be relevant to vitamin A transport by full-length ^CaCaM-STRA6.     

Changes of cationic transport in <Emphasis Type="Italic">AtCAX5</Emphasis> transformant yeast by electromagnetic field environments

The electromagnetic field (EMF) is newly considered as an exogenous environmental stimulus that is closely related to ion transportation on the cellular membrane, maintaining the internal ionic homeostasis. Cation transports of Ca²⁺ and other metal ions, Cd²⁺, Zn²⁺, and Mn²⁺were studied in terms of the external Ca²⁺ stress, [Ca²⁺]_ext, and exposure to the physical EMF. A specific yeast strain K667 was used for controlling CAX5 (cation/H⁺ exchanger) expression. Culture samples were exposed to 60 Hz, 0.1 mT sinusoidal or square magnetics waves, and intracellular cations of each sample were measured and analyzed. AtCAX5 transformant yeast grew normally under the metallic stress. However, the growth of the control group was significantly inhibited under the same cation concentration; 60 Hz and 0.1 mT magnetic field enhanced intracellular cation concentrations significantly as exposure time increased both in the AtCAX5 transformed yeast and in the control group. However, the AtCAX5-transformed yeast showed higher concentration of the intracellular cations than the control group under the same exposure EMF. AtCAX5-transformed yeasts displayed an increment in [Ca²⁺]_int, [K⁺]_int, [Na⁺]_int, and [Zn²⁺]_int concentration under the presence of both sinusoidal and square-waved EMF stresses compared to the control group, which shows that AtCAX5 expressed in the vacuole play an important role in maintaining the homeostasis of intracellular cations. These findings could be utilized in the cultivation of the crops which were resistant to excessive exogenous ions or in the production of biomass containing a large proportion of ions for nutritional food or in the bioremediation process in metal-polluted environments.     

间伐强度对秦岭锐齿栎林冠层和枯落物层水化学效应的影响

将森林抚育间伐与森林水化学效应结合起来进行研究,探讨小强度间伐对森林水质的影响。基于固定样地的研究方法,在秦岭火地塘林区选择天然锐齿栎林,设置抚育间伐强度分别为5%、10%、15%和20%的样地和对照样地,定期采集大气降雨、林内雨和枯透水样品,测定其水化学物质浓度,采用对比分析的方法,研究间伐强度对锐齿栎林内雨和枯透水化学效应的影响。结果表明:间伐样地林内雨和枯透水的pH值均低于对照样地,呈弱酸性,在5%的间伐强度下,森林冠层和枯落物层对大气降雨pH值的调升作用较显著,随着间伐强度的增加,调升幅度逐渐减小;大气降雨对森林冠层和枯落物层中的SO_4~(2-)、NO_3~-和PO_4~(3-)均具有淋溶作用,尤其是对照样地林内雨和枯透水中SO_4~(2-)的浓度增幅最显著,NO_3~-次之,PO_4~(3-)最不显著。间伐样地,雨水对林冠层和枯落物层SO_4~(2-)、NO_3~-和PO_4~(3-)的淋溶作用均低于对照样地,20%的间伐强度最有利于净化雨水中的SO_4~(2-),其在林内雨和枯透水中的含量较对照样地降幅最大,间伐强度为5%时,林内雨中NO_3~-、NH_4~+和PO_4~(3-)的含量最低,三者较对照样地的含量分别降低了56.3%、46%和9.2%而枯透水中三者的降幅分别为64.6%、45%和60.8%;在10%的间伐强度下,大气降雨对林冠层和枯落物层中K~+、Ca~(2+)、Mg~(2+)的淋溶作用最强,3种离子中以Ca~(2+)和Mg~(2+)的含量增幅最为显著。林内雨中Ca~(2+)和Mg~(2+)的含量分别较对照样地增加了89.9%和120%,枯透水中二者较对照样地分别增加了72.4%和40%,K~+的增幅相对不明显;大气降雨中的Pb~(2+)、Zn~(2+)和Cd~(2+)经过森林冠层和枯落物层的阻减,其在林内雨和枯透水中的含量随着间伐强度的增加呈先增大后减小的趋势,当间伐强度达到20%时,三者含量明显降低。总体上,20%的间伐强度最有利于森林冠层及枯落物层对重金属Pb~(2+)、Zn~(2+)和Cd~(2+)的截留净化。     

Heavy metal ions affect the activity of DNA glycosylases of the Fpg family

Prokaryotic enzymes formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease VIII (Nei) and their eukaryotic homologs NEIL1, NEIL2, and NEIL3 define the Fpg family of DNA glycosylases, which initiate the process of repair of oxidized DNA bases. The repair of oxidative DNA lesions is known to be impaired in vivo in the presence of ions of some heavy metals. We have studied the effect of salts of several alkaline earth and transition metals on the activity of Fpg-family DNA glycosylases in the reaction of excision of 5,6-dihydrouracil, a typical DNA oxidation product. The reaction catalyzed by NEIL1 was characterized by values K _m = 150 nM and k _cat = 1.2 min⁻¹, which were in the range of these constants for excision of other damaged bases by this enzyme. NEIL1 was inhibited by Al³⁺, Ni²⁺, Co²⁺, Cd²⁺, Cu²⁺, Zn²⁺, and Fe²⁺ in Tris-HCl buffer and by Cd²⁺, Zn²⁺, Cu²⁺, and Fe²⁺ in potassium phosphate buffer. Fpg and Nei, the prokaryotic homologs of NEIL1, were inhibited by the same metal ions as NEIL1. The values of I₅₀ for NEIL1 inhibition were 7 μM for Cd²⁺, 16 μM for Zn²⁺, and 400 μM for Cu²⁺. The inhibition of NEIL1 by Cd²⁺, Zn²⁺, and Cu²⁺ was at least partly due to the formation of metal-DNA complexes. In the case of Cd²⁺ and Cu²⁺, which preferentially bind to DNA bases rather than phosphates, the presence of metal ions caused the enzyme to lose the ability for preferential binding to damaged DNA. Therefore, the inhibition of NEIL1 activity in removal of oxidative lesions by heavy metal ions may be a reason for their comutagenicity under oxidative stress.     

Selectivty Assessments of a Sequential Extraction Procedure for Potential Trace Metals’ Mobility and Bioavailability in Phosphate Rocks from Jordan Phosphate Mines

A modified six-step sequential extraction procedure was used to fractionate and determine the following trace metals: U⁴⁺, As⁵⁺, Cd²⁺, Cr⁺², Cu²⁺, Ni²⁺, Pb²⁺, Zn²⁺, and V⁵⁺ in three different phosphate rocks from mines in Jordan. The mean values of uranium in the samples investigated were 98 ± 6 mgkg^?1, 92 ± 3 mgkg^?1, 215 ± 6 mgkg^?1, and 159 ± 13 mgkg^?1, respectively. The sequential extraction results obtained showed that most of the U⁴⁺ in these samples was strongly bound with 87%, 93%, 97%, and 93% of the total content, respectively, remaining in the samples after the sequential extraction steps were performed. Hence, 13%–7% and 3%–7%, respectively, of the U⁴⁺ is distributed in the most labile form, indicating that the majority of the U⁴⁺ in these samples was highly incorporated within the apatite present in the samples. The aforementioned was in agreement with the XRD and SEM-EDX results obtained. The apparent mobility of U⁴⁺, As⁵⁺, Cd²⁺, Cr⁺², Cu²⁺, Ni²⁺, Pb²⁺, Zn²⁺, and V⁵⁺ (using all six extraction steps) from the Al-Abied and Al-Hasa samples was as follows: As⁵⁺ (30.17%)> Cu²⁺ (6.55%)> Zn²⁺(4.34%)> Cd²⁺ (3.84%) Cr⁺² (3.66%)> Pb²⁺ (2.57%)> V⁵⁺ (53%)> Ni²⁺ (1.71%)> U⁴⁺ (0.99%). The mobility of As⁵⁺, Cd²⁺, Cu²⁺, Cr⁺², Ni²⁺, Pb²⁺, U⁴⁺, Zn²⁺, and V⁵⁺ (using all six extraction steps) from Eshidiya samples was as follows: As⁵⁺ (17.32%)> Cr⁺² (4.84%)> Zn²⁺ (4.25%)> Pb²⁺ (4.19%)> Cu²⁺ (3.49%)> V⁵⁺ (1.42%)> Cd²⁺ (0.78) U⁴⁺ (0.09%)> Ni²⁺ (0%).     

Heterologous Expression and Metal-Binding Characterization of a Type 1 Metallothionein Isoform (OsMTI-1b) from Rice (Oryza sativa)

Metallothioneins (MTs) are ubiquitous, low molecular mass and cysteine-rich proteins that play important roles in maintaining intracellular metal homeostasis, eliminating metal toxification and protecting the cells against oxidative damages. MTs are able to bind metal ions through the thiol groups of their cysteine residues. Plants have several MT isoforms which are classified into four types based on the arrangement of cysteine residues. In the present study, a rice (Oryza sativa) gene encoding type 1 MT isoform, OsMTI-1b, was inserted in vector pET41a and overexpressed in Escherichia coli as carboxy-terminal extensions of glutathione-S-transferase (GST). The recombinant protein GST-OsMTI-1b was purified using affinity chromatography and its ability to bind with Ni²⁺, Cd²⁺, Zn²⁺ and Cu²⁺ ions was analyzed. The results demonstrated that this isoform has ability to bind Ni²⁺, Cd²⁺ and Zn²⁺ ions in vitro, whereas it has no substantial ability to bind Cu²⁺ ions. From competitive reaction with 5,5′-dithiobis(2-nitrobenzoic acid), DTNB, the affinity of metal ions for recombinant form of GST-OsMTI-1b was as follows: Ni²⁺/Cd²⁺ > Zn²⁺ > Cu²⁺     

Some metals inhibit the glutathione S‐transferase from Van Lake fish gills

Glutathione S‐transferases (GSTs) are the superfamily of multifunctional detoxification isoenzymes and play important role cellular signaling. The present article focuses on the role of Cd²⁺, Cu²⁺, Zn²⁺, and Ag⁺ in vitro inhibition of GST. For this purpose, GST was purified from Van Lake fish (Chalcalburnus tarichii Pallas) gills with 110.664 EU mg^?1 specific activity and 79.6% yield using GSH‐agarose affinity chromatographic method. The metal ions were tested at various concentrations on in vitro GST activity. IC₅₀ values were found for Cd⁺², Cu⁺², Zn⁺², Ag⁺ as 450.32, 320.25, 1510.13, and 16.43 μM, respectively. K _i constants were calculated as 197.05 ± 105.23, 333.10 ± 152.76, 1670.21 ± 665.43, and 0.433 ± 0.251 μM, respectively. Ag⁺ showed better inhibitory effect compared with the other metal ions. The inhibition mechanisms of Cd²⁺ and Cu²⁺ were non‐competitive, whereas Zn²⁺ and Ag⁺ were competitive. Co²⁺, Cr²⁺, Pb²⁺, and Fe³⁺ had no inhibitory activity on GST.     

Differential effects of heavy metal ions on Ca2+-dependent K+ channels

Summary 1. The ability of various divalent metal ions to substitute for Ca²⁺ in activating distinct types of Ca²⁺-dependent K⁺ [K⁺(Ca²⁺] channels has been investigated in excised, inside-out membrane patches of human erthrocytes and of clonal N1E-115 mouse neuroblastoma cells using the patch clamp technique. The effects of the various metal ions have been compared and related to the effects of Ca²⁺.2. At concentrations between 1 and 100 µM Pb²⁺, Cd²⁺ and Co²⁺ activate intermediate conductance K⁺(Ca²⁺) channels in erythrocytes and large conductance K⁺(Ca²⁺) channels in neuroblastoma cells. Pb²⁺ and Co²⁺, but not Cd²⁺, activate small conductance K⁺(Ca²⁺) channels in neuroblastoma cells. Mg²⁺ and Fe²⁺ do not activate any of the K⁺(Ca²⁺) channels.3. Rank orders of the potencies for K⁺(Ca²⁺) activation are Pb²⁺, Cd²⁺>Ca²⁺, Co²⁺>>Mg²⁺, Fe²⁺ for the intermediate erythrocyte K⁺(Ca²⁺) channel, and Pb²⁺, Cd²⁺>Ca²⁺>Co²⁺>>Mg²⁺, Fe²⁺ for the small, and Pb²⁺>Ca²⁺>Co²⁺>>Cd²⁺, Mg²⁺, Fe²⁺ for the large K⁺(Ca²⁺) channel in neuroblastoma cells.4. At high concentrations Pb²⁺, Cd²⁺, and Co²⁺ block K⁺(Ca²⁺) channels in erythrocytes by reducing the opening frequency of the channels and by reducing the single channel amplitude. The potency orders of the two blocking effects are Pb²⁺>Cd²⁺, Co²⁺>>Ca²⁺, and Cd²⁺>Pb²⁺, Co²⁺>>Ca²⁺, respectively, and are distinct from the potency orders for activation.5. It is concluded that the different subtypes of K⁺(Ca²⁺) channels contain distinct regulatory sites involved in metal ion binding and channel opening. The K⁺(Ca²⁺) channel in erythrocytes appears to contain additional metal ion interaction sites involved in channel block.     

Partial Purification and Characterization of Chromate Reductase of a Novel Ochrobactrum sp. Strain Cr-B4

Hexavalent chromium contamination is a serious problem due to its high toxicity and carcinogenic effects on the biological systems. The enzymatic reduction of toxic Cr(VI) to the less toxic Cr(III) is an efficient technology for detoxification of Cr(VI)-contaminated industrial effluents. In this regard, a chromate reductase enzyme from a novel Ochrobactrum sp. strain Cr-B4, having the ability to detoxify Cr(VI) contaminated sites, has been partially purified and characterized. The molecular mass of this chromate reductase was found to be 31.53 kD, with a specific activity 14.26 U/mg without any addition of electron donors. The temperature and pH optima for chromate reductase activity were 40°C and 8.0, respectively. The activation energy (E_a) for the chromate reductase was found to be 34.7 kJ/mol up to 40°C and the activation energy for its deactivation (E_d) was found to be 79.6 kJ/mol over a temperature range of 50–80°C. The frequency factor for activation of chromate reductase was found to be 566.79 s^?1, and for deactivation of chromate reductase it was found to be 265.66 × 10³ s^?1. The reductase activity of this enzyme was affected by the presence of various heavy metals and complexing agents, some of which (ethylenediamine tetraacetic acid [EDTA], mercaptoethanol, NaN₃, Pb²⁺, Ni²⁺, Zn²⁺, and Cd²⁺) inhibited the enzyme activity, while metals like Cu²⁺ and Fe³⁺ significantly enhanced the reductase activity. The enzyme followed Michaelis–Menten kinetics with K_m of 104.29 µM and a V_max of 4.64 µM/min/mg.