Petiolar felt-sheath of palm: a new biosorbent for the removal of heavy metals from contaminated water.

Biosorption of heavy metals such as Pb2+, Ni2+, Cd2+, Cu2+, Cr3+ and Zn2+ by petiolar felt-sheath of palm (PFP) from contaminated water was examined. PFP was found to efficiently remove all the toxic metal ions with selectivity order of Pb2+ > Cd2+ > Cu2+ > Zn2+ > Ni2+ > Cr3+. The uptake was rapid, with more than 70% completed within 15 min. The bound metal ions were successfully desorbed and the PFP fibrous-biomass remained effective after several adsorption-desorption cycles.     

The cobalt, zinc, and cadmium efflux system CzcABC from Alcaligenes eutrophus functions as a cation-proton antiporter in Escherichia coli.

The function of the CzcABC protein complex, which mediates resistance to Co2+, Zn2+, and Cd2+ in Alcaligenes eutrophus by cation efflux, was investigated by using everted membrane vesicles of Escherichia coli and an acridine orange fluorescence quenching assay. Since metal cation uptake could not be measured with inside-out membrane vesicles prepared from A. eutrophus and since available E. coli strains did not express the Czc-mediated resistance to cobalt, zinc, and cadmium salts, mutants of E. coli which exhibited a Czc-dependent increase in heavy metal resistance were isolated. E. coli mutant strain EC351 constitutively accumulated Co2+, Zn2+, and Cd2+. In the presence of Czc, net uptake of these heavy metal cations was reduced to the wild-type level. Inside-out vesicles prepared from E. coli EC351 cells displayed a Czc-dependent uptake of Co2+, Zn2+, and Cd2+ and a cation-triggered acridine orange fluorescence increase. The czc-encoded protein complex CzcABC was shown to be a zinc-proton antiporter.     

The role of divalent cations in structure and function of murine adenosine deaminase.

For murine adenosine deaminase, we have determined that a single zinc or cobalt cofactor bound in a high affinity site is required for catalytic function while metal ions bound at an additional site(s) inhibit the enzyme. A catalytically inactive apoenzyme of murine adenosine deaminase was produced by dialysis in the presence of specific zinc chelators in an acidic buffer. This represents the first production of the apoenzyme and demonstrates a rigorous method for removing the occult cofactor. Restoration to the holoenzyme is achieved with stoichiometric amounts of either Zn2+ or Co2+ yielding at least 95% of initial activity. Far UV CD and fluorescence spectra are the same for both the apo- and holoenzyme, providing evidence that removal of the cofactor does not alter secondary or tertiary structure. The substrate binding site remains functional as determined by similar quenching measured by tryptophan fluorescence of apo- or holoenzyme upon mixing with the transition state analog, deoxycoformycin. Excess levels of adenosine or N6- methyladenosine incubated with the apoenzyme prior to the addition of metal prevent restoration, suggesting that the cofactor adds through the substrate binding cleft. The cations Ca2+, Cd2+, Cr2+, Cu+, Cu2+, Mn2+, Fe2+, Fe3+, Pb2+, or Mg2+ did not restore adenosine deaminase activity to the apoenzyme. Mn2+, Cu2+, and Zn2+ were found to be competitive inhibitors of the holoenzyme with respect to substrate and Cd2+ and Co2+ were noncompetitive inhibitors. Weak inhibition (Ki > or = 1000 microM) was noted for Ca2+, Fe2+, and Fe3+.     

Evidence for a zinc/proton antiporter in rat brain

The data presented in this paper are consistent with the existence of a plasma membrane zinc/proton antiport activity in rat brain. Experiments were performed using purified plasma membrane vesicles isolated from whole rat brain. Incubating vesicles in the presence of various concentrations of 65Zn2+ resulted in a rapid accumulation of 65Zn2+. Hill plot analysis demonstrated a lack of cooperativity in zinc activation of 65Zn2+ uptake. Zinc uptake was inhibited in the presence of 1 mM Ni2+, Cd2+, or CO2+. Calcium (1 mM) was less effective at inhibiting 65Zn2+ uptake and Mg2+ and Mn2+ had no effect. The initial rate of vesicular 65Zn2+ uptake was inhibited by increasing extravesicular H+ concentration. Vesicles preloaded with 65Zn2+ could be induced to release 65Zn2+ by increasing extravesicular H+ or addition of 1 mM nonradioactive Zn2+. Hill plot analysis showed a lack of cooperativity in H+ activation of 65Zn2+ release. Based on the Hill analyses, the stoichiometry of transport may include Zn2+/Zn2+ exchange and Zn2+/H+ antiport, the latter being potentially electrogenic. Zinc/proton antiport may be an important mode of zinc uptake into neurons and contribute to the reuptake of zinc to replenish presynaptic vesicle stores after stimulation.     

芦竹对不同重金属耐性的研究

研究芦竹(Arundo donax)在不同重金属污染湿地中的耐毒性能,测定了不同生长时段芦竹的生物性状和叶绿素含量,以及土壤中重金属含量的变化.结果表明,芦竹分别在浓度为100 mg·kg^-1左右的CuCu²⁺、Pb²⁺、Cd²⁺、Zn²⁺、Ni²⁺、Hg²⁺和50 mg·kg^-1以下的Cr⁶⁺污染环境中能正常成活,在40 d的生长期内,植物体内叶绿素有不同程度降低,下降比率在20%～56%,植物出现叶片软化,叶尖枯黄等症状,但植株仍呈现增长趋势.与对照植物相比较,在重金属胁迫下,植株细长,茎、叶呈黄绿色,除Cr⁶⁺、Hg²⁺外,植物高度基本不受重金属胁迫的影响.芦竹在高浓度(100mg·kg^-1)Cr⁶⁺污染环境中耐性较弱,表现出生长缓慢,部分地下茎腐烂,叶片短时间内出现枯萎等症状.结果还表明,土壤中重金属浓度随植物生长期增长而降低,除被植物吸收,植物挥发外,还存在着重金属向根际圈环境迁移的趋势,根周边湿土中重金属含量,明显高于试验缸外围湿土中重金属含量.可以认为,芦竹具有生物量大,根系发达,适应性强等特点,对修复湿地重金属污染蕴藏着巨大潜力,研究芦竹在植物修复技术中的应用,具有一定的现实意义.     

Cloning of three ZIP/Nramp transporter genes from a Ni hyperaccumulator plant Thlaspi japonicum and their Ni2+-transport abilities.

Ni homeostasis is essential for plant cell activity, but the mechanisms of Ni-transport and delivery are unknown. To elucidate the role of ZIP and NRAMP metal-transporters for Ni2+-transport and homeostasis, we cloned their homologous genes from the Ni hyperaccumulator Thlaspi japonicum, and investigated their Ni-transporting abilities by expression in yeast. The deduced amino acid sequences of the two Zip transporter genes (TjZnt1, TjZnt2) and one Nramp transporter gene cloned had high homologies with TcZNT1 and TcZNT2 of Thlaspi caerulescens and AtNRAMP4 of Arabidopsis thaliana, respectively, and were predicted as integral membrane proteins with 6 or 12 transmembrane domains. TjZNT1 and TjZNT2 had two long histidine-rich domains in the putative cytoplasmic domain between transmembrane domains III and IV. TjNRAMP4 conserved a consensus transporter motif between transmembrane domains VIII and IX. The yeast transformed with TjZNT1 or TjZNT2 showed a marked increase in Ni2+ tolerance with the gene expression. In contrast, the expression of TjNramp4 caused elevation of Ni2+ sensitivity and Ni2+ concentration. These data suggest that ZIP/NRAMP transporters participate in Ni2+ homeostasis of Ni hyperaccumulator plants. TjZNT1 had Zn2+-, Cd2+- and Mn2+-transporting abilities and TjZNT2 also had Zn2+- and Mn2+-transporting abilities, but TjNRAMP4 could transport Ni2+ but not Zn2+, Cd2+ or Mn2+.     

重金属胁迫条件下空心莲子草的生长和营养特征分析

空心莲子草是一种常见的水生植物,并能在重金属污染的水体或附近土壤中生长.本研究发现,空心莲子草能富集6种常见的重金属元素,其富集能力为:Zn2+>Mn2+>Pb2+>Cu2+>Cd2+>Cr3+.高浓度(1 mmol/L) Cu2+、Mn2+、Zn2+和Cr3+ 等重金属胁迫处理条件下,空心莲子草的根冠比增加,生物干重、总根长和总根表面积都相应降低.此外,高浓度(1 mmol/L) Pb2+、Cd2+、Cu2+或Zn2+分别胁迫处理条件下,空心莲子草的K+、Ca+和Mg+等元素的含量变化差异显著(P＜0.05).以上研究表明,空心莲子草通过改变体内钾钙镁等重要生长元素营养情况来适应重金属污染的胁迫,有很强的富集重金属元素的能力,进而降低污染、净化水体.空心莲子草对重金属污染的生长响应及体内重要矿物元素营养特性之间的相互关系,可能为重金属污染的水土生物修复提供理论依据.     

重金属诱导拟南芥原生质体DNA 损伤的单细胞凝胶电泳检测

以拟南芥原生质体为实验体系, 研究不同浓度的3种重金属离子对拟南芥原生质体的毒性和DNA损伤的差异。结果表明, 用1-5 mmol.L-1的Zn2+、Cd2+ 和Cu2+分别处理的拟南芥原生质体, 2 小时内活力逐渐下降, 并表现出明显的浓度依赖性;与相同浓度的Cd2+ 和Cu2+ 相比, Zn2+对拟南芥原生质体活力的影响程度较小, 表现出较低的毒性。单细胞凝胶电泳检测发现,用0.1-0.8 mmol .L-1的Zn2+、Cd2+ 和Cu2+ 分别处理拟南芥原生质体30 分钟, 以OTM值表示的原生质体DNA损伤量随重金属离子浓度的增加而递增; 相同浓度(0.5 mmol.L-1)的3种重金属离子相比, Zn2+对原生质体的遗传毒性明显低于Cu2+ 和Cd2+。综合原生质体活力和DNA损伤的单细胞凝胶电泳检测结果, 发现Zn2+对拟南芥原生质体的遗传毒性较低, 而Cd2+ 和Cu2+的遗传毒性较高。本研究建立的拟南芥原生质体实验体系, 结合运用单细胞凝胶电泳技术, 能够快速、灵敏地检测重金属对植物细胞的遗传毒性。     

Biosorption of chromium, copper, manganese and zinc by Pseudomonas aeruginosa AT18 isolated from a site contaminated with petroleum

The study describes the sorption of Cr, Cu, Mn and Zn by Pseudomonas aeruginosa AT18 isolated from a site contaminated with petroleum and heavy metals. The concentrations studied were 50, 49, 60 and 70 (mg L(-1)) for Cr, Cu, Mn and Zn, respectively. The solution pH and ionic strength were very important factors in the metal biosorption performance and the biosorption capacity of P. aeruginosa AT18 for Cr3+,Cu2+, Mn2+ and Zn2+. In aqueous solution, the biosorption increased with increasing pH in the range 5.46-7.72. The results obtained in the experimental assays show that P. aeruginosa AT18 has the capacity for biosorption of the metallic ions Cr3+, Cu2+ and Zn2+ in solutions, although its capacity for the sorption of manganese is low (22.39 mg Mn2+/g of biomass) in comparison to the Cr3+, Cu2+ and Zn2+ ions, as shown by the individual analyses. However, 20% of the manganese was removed from an initial concentration of 49.0 mg L(-1), with a Qm value similar to that obtained in solutions containing mixtures of Cr3+, Cu2+, Mn2+and Zn2+. The chromium level sorbed by P. aeruginosa AT18 biomass was higher than that for Cu, Mn and Zn, with 100% removal in the pH range 7.00-7.72 and a Qm of 121.90-200.00 mg of Cr3+/g of biomass. The removal of Cr, Cu and Zn is also a result of precipitation processes.     

L-threonine dehydrogenase from Escherichia coli. Identification of an active site cysteine residue and metal ion studies

Pure L-threonine dehydrogenase from Escherichia coli is a tetrameric protein (Mr = 148,000) with 6 half-cystine residues/subunit; its catalytic activity as isolated is stimulated 5-10-fold by added Mn2+ or Cd2+. The peptide containing the 1 cysteine/subunit which reacts selectively with iodoacetate, causing complete loss of enzymatic activity, has been isolated and sequenced; this cysteine residue occupies position 38. Neutron activation and atomic absorption analyses of threonine dehydrogenase as isolated in homogeneous form now show that it contains 1 mol of Zn2+/mol of enzyme subunit. Removal of the Zn2+ with 1,10-phenanthroline demonstrates a good correlation between the remaining enzymatic activity and the zinc content. Complete removal of the Zn2+ yields an unstable protein, but the native metal ion can be exchanged by either 65Zn2+, Co2+, or Cd2+ with no change in specific catalytic activity. Mn2+ added to and incubated with the native enzyme, the 65Zn2(+)-, the Co2(+)-, or the Cd2(+)- substituted form of the enzyme stimulates dehydrogenase activity to the same extent. These studies along with previously observed structural homologies further establish threonine dehydrogenase of E. coli as a member of the zinc-containing long chain alcohol/polyol dehydrogenases; it is unique among these enzymes in that its activity is stimulated by Mn2+ or Cd2+.     

The effect of divalent cations on bovine spermatozoal adenylate cyclase activity.

The effect of divalent cations on bovine sperm adenylate cyclase activity was studied. Mn2+, Co2+, Cd2+, Zn2+, Mg2+ and Ca2+ were found to satisfy the divalent cation requirement for catalysis of the bovine sperm adenylate cyclase. These divalent cations in excess of the amount necessary for the formation of the metal-ATP substrate complex were found to stimulate the enzyme activity to various degrees. The magnitude of stimulation at saturating concentrations of the divalent cations was strikingly greater with M2+ than with either Ca2+, Mg2+, Zn2+, Cd2+ or Co2+. The apparent Km was lowest for Zm2+ (0.1 - 0.2 mM) than for any of the other divalent cations tested (1.2 - 2.3 mM). The enzyme stimulation by Mn2+ was decreased by the simultaneous addition of Co2+, Cd2+, Ni2+ and particularly Zn2+ and Cu2+. The antagonism between Mn2+ and Cu2+ or Zn2+ appeared to have both competitive and non-competitive features. The inhibitory effect of Cu2+ on Mn2+-stimulated adenylate cyclase activity was prevented by 2,3-dimercaptopropanol, but not by dithiothreitol, L-ergothioneine, EDTA, EGTA or D-penicillamine. Ca2+ at concentrations of 1-5 mM was found to act synergistically with Mg2+, Zn2+, Co2+ and Mn2+ in stimulating sperm adenylate cyclase activity. The Ca2+ augmentation of the stimulatory effect of Zn2+, Co2+, Mg2+ and Mn2+ appeared to be specific.     

匍茎翦股颖对Cu2+、Zn2+、Cd2+与Pb2+ 胁迫的生长响应与阈限浓度

采用砂培法,研究了匍茎翦股颖对Cu2+、Zn2+、Cd2+与Pb2+胁迫的生长响应及阈限浓度,结果表明:种子萌发率随着4种重金属浓度的增加而下降。对株高的影响是当重金属浓度小于100mg/L时会促进株高生长,高于100mg/L则产生抑制作用。Cu2+显著抑制根系生长,并随浓度的增加抑制效应愈加显著;在Cu2+浓度为600mg/L时匍茎翦股颖的根长比对照下降了93.75%。Cu2+、Zn2+、Pb2+浓度小于200mg/L时会促进地上生物量的增加,但高于200mg/L时,地上生物量会随着3种重金属的增加而减少。Cu2+、Zn2+浓度小于100mg/L或Cd2+、Pb2+浓度小于200mg/L会增加叶绿素的含量,高浓度会降低叶绿素的含量;Cd2+在浓度为600mg/L时显著降低叶绿素含量,与对照相比,下降了43.55%。匍茎翦股颖生长的综合效应分析表明,匍茎翦股颖对Cu2+胁迫最敏感,具有较低的阈限浓度,而Zn2+胁迫对匍茎翦股颖的生长影响最小,阈限浓度相对较高。     

The functional role of zinc in angiotensin converting enzyme: implications for the enzyme mechanism

Zinc is essential to the catalytic activity of angiotensin converting enzyme. The enzyme contains one g-atom of zinc per mole of protein. Chelating agents abolish activity by removing the metal ion to yield the inactive, metal-free apoenzyme. Zinc does not stabilize protein structure since the native and apoenzymes are equally susceptible to heat denaturation. Addition of either Zn2+, Co2+, or Mn2+ to the apoenzyme generates an active metalloenzyme; Fe2+, Ni2+, Cu2+, Cd2+, and Hg2+ fail to restore activity. The activities of the metalloenzymes follow the order Zn greater than Co greater than Mn. The protein binds Zn2+ more firmly than it does Co2+ or Mn2+. Hydrolysis of the chromophoric substrate, furanacryloyl-Phe-Gly-Gly, by the active metalloenzymes is subject to chloride activation; the activation constant is not metal dependent. Metal replacement mainly affects Kcat with very little change in Km, indicating that the role of zinc is to catalyze peptide hydrolysis.     

Binding of manganese in human and rat plasma

Albumin, transferrin and 'transmanganin' have all been proposed as the major Mn-binding ligand in plasma. The present investigations were initiated in order to resolve these discrepancies. Compared to other metals tested (109 Cd2+, 65Zn2+, 59Fe3+), 54Mn2+ bound poorly to purified albumin. The addition of exogenous albumin to plasma did not result in an increased 54Mn radioactivity associated with this protein. Also, incubation of 65Zn-albumin in the presence of excess Mn2+ (1 mM) did not result in the displacement of Zn from albumin or Mn binding. In contrast to these results, 54Mn was bound to purified transferrin, not as readily as Fe3+, but better than Zn2+ or Cd2+. Saturation of transferrin with Fe3+ (1.6 micrograms Fe/mg) prevented the binding of 54Mn indicating that Mn probably binds to Fe-binding sites on the protein. Polyacrylamide gel electrophoresis further demonstrated the association of 54Mn with transferrin rather than with albumin in both human and rat plasma. The amount of 54Mn radioactivity recovered with transferrin increased as incubation time was increased, probably due to oxidation of Mn2+ to Mn3+. Mn binding to transferrin reached a maximum within 5 and 12 h of incubation. About 50% of 54Mn migrated with transferrin, whereas only 5% was associated with albumin. A significant portion (20-55%) of the 54Mn radioactivity migrated with electrophoretically slow plasma components whose identity was not determined. Possibilities include alpha 2-macroglobulin, heavy gamma-globulins and/or heavy lipoproteins.     

Extracellular zinc triggers ERK-dependent activation of Na+/H+ exchange in colonocytes mediated by the zinc-sensing receptor

Extracellular zinc promotes cell proliferation and its deficiency leads to impairment of this process, which is particularly important in epithelial cells. We have recently characterized a zinc-sensing receptor (ZnR) linking extracellular zinc to intracellular release of calcium. In the present study, we addressed the role of extracellular zinc, acting via the ZnR, in regulating the MAP kinase pathway and Na+/H+ exchange in colonocytes. We demonstrate that Ca2+ release, mediated by the ZnR, induces phosphorylation of ERK1/2, which is highly metal-specific, mediated by physiological concentrations of extracellular Zn2+ but not by Cd2+, Fe2+, Ni2+, or Mn2+. Desensitization of the ZnR by Zn2+, is followed by approximately 90% inhibition of the Zn2+ -dependent ERK1/2 phosphorylation, indicating that the ZnR is a principal link between extracellular Zn2+ and ERK1/2 activation. Application of both the IP3 pathway and PI 3-kinase antagonists largely inhibited Zn2+ -dependent ERK1/2 phosphorylation. The physiological significance of the Zn2+ -dependent activation of ERK1/2 was addressed by monitoring Na+/H+ exchanger activity in HT29 cells and in native colon epithelium. Preincubation of the cells with zinc was followed by robust activation of Na+/H+ exchange, which was eliminated by cariporide (0.5 microm); indicating that zinc enhances the activity of NHE1. Activation of NHE1 by zinc was totally blocked by the ERK1/2 inhibitor, U0126. Prolonged acidification, in contrast, stimulates NHE1 by a distinct pathway that is not affected by extracellular Zn2+ or inhibitors of the MAP kinase pathway. Desensitization of ZnR activity eliminates the Zn2+ -dependent, but not the prolonged acidification-dependent activation of NHE1, indicating that Zn2+ -dependent activation of H+ extrusion is specifically mediated by the ZnR. Our results support a role for extracellular zinc, acting through the ZnR, in regulating multiple signaling pathways that affect pH homeostasis in colonocytes. Furthermore activation of both, ERK and NHE1, by extracellular zinc may provide the mechanism linking zinc to enhanced cell proliferation.     

Cadmium uptake in Escherichia coli K-12.

109Cd2+ uptake by Escherichia coli occurred by means of an active transport system which has a Km of 2.1 microM Cd2+ and a Vmax of 0.83 mumol/min X g (dry weight) in uptake buffer. 109Cd2+ accumulation was both energy dependent and temperature sensitive. The addition of 20 microM Cd2+ or Zn2+ (but not Mn2+) to the cell suspensions preloaded with 109Cd2+ caused the exchange of Cd2+. 109Cd2+ (0.1 microM) uptake by cells was inhibited by the addition of 20 microM Zn2+ but not Mn2+. Zn2+ was a competitive inhibitor of 109Cd2+ uptake with an apparent Ki of 4.6 microM Zn2+. Although Mn2+ did not inhibit 109Cd2+ uptake, the addition of either 20 microM Cd2+ or Zn2+ prevented the uptake of 0.1 microM 54Mn2+, which apparently occurs by a separate transport system. The inhibition of 54Mn2+ accumulation by Cd2+ or Zn2+ did not follow Michaelis-Menten kinetics and had no defined Ki values. Co2+ was a competitive inhibitor of Mn2+ uptake with an apparent Ki of 34 microM Co2+. We were unable to demonstrate an active transport system for 65Zn2+ in E. coli.