蚕豆气孔运动中水通道和离子通道的作用和地位的探讨

 用不同浓度HgCl2、LaCl3和TEACl (Tetraethylammonium chloride)处理蚕豆(Vicia faba)叶片下表皮条,发现HgCl2能显著抑制气孔开闭,Ca2+通道阻塞剂LaCl3或K+通道阻塞剂TEACl处理也都有一定程度的抑制。三者的作用效果HgCl2>>LaCl3>TEACl。用HgCl2+LaCl3、HgCl2+TEACl或HgCl2+LaCl3+TEACl处理,则气孔开闭运动几乎完全被抑制。表明：蚕豆气孔运动中,保卫细胞胀缩主要是水通道直接参与保卫细胞与叶肉细胞间水流的调节引起的,离子通道起间接次要作用,二者共同引起保卫细胞体积变化而导致气孔开闭。     

Effects of heavy metals on the Ca2+-ATPase activity present in gill cell plasma-membrane of mussels (Mytilus galloprovincialis Lam.)

1. Heavy metals (Hg²⁺, Cu²⁺, Cd²⁺, Zn²⁺, Pb²⁺) at micromolar concentrations strongly inhibit the Ca²⁺-ATPase activity present in the plasma-membrane obtained from the gill cells of Mytilus galloprovincialis Lam. Heavy metals act through inhibition of the formation of the phosphorylated intermediate.2. All the heavy metals tested inhibit the Ca²⁺-ATPase activity, the effect following the order: Hg²⁺ > Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺; the simultaneous addition of different heavy metals causes a summatory inhibition of the enzyme activity; addition to the reaction mixture of GSH at a final concentration of 0.5 mM, reverses inhibitory effects of heavy metals.3. The inhibitory effects of Cu²⁺ on Ca²⁺-ATPase are highly enhanced by addition of ascorbate to the reaction mixture. In the presence of ascorbate (100 μM), copper strongly stimulates the lipid peroxidation damage of the gill plasma-membranes, a result that may explain the high copper cytotoxicity.     

Effects of heavy metals on seed germination and early seedling growth of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Seed is a developmental stage that is highly protective against external stresses in the plant life cycle. In this study, we analyzed toxicity of essential (Cu²⁺ and Zn²⁺) and non-essential heavy metals (Hg²⁺, Pb²⁺ and Cd²⁺) on seed germination and seedling growth in the model species Arabidopsis. Our results show that seedling growth is more sensitive to heavy metals (Hg²⁺, Pb²⁺, Cu²⁺ and Zn²⁺) in comparison to seed germination, while Cd²⁺ is the exception that inhibited both of these processes at similar concentrations. To examine if toxicity of heavy metals is altered developmentally during germination, we incubated seeds with Hg²⁺ or Cd²⁺ only for a restricted period during germination. Hg²⁺ displayed relatively strong toxicity at period II (12–24 h after imbibition), while Cd²⁺ was more effective to inhibit germination at period I (0–12 h after imbibition) rather than at period II. The observed differences are likely to be due in part to selective uptake of different ions by the intact seed, because isolated embryos (without seed coat and endosperm) are more sensitive to both Hg²⁺ and Cd²⁺ at period I. We assessed interactive toxicity between heavy metals and non-toxic cations, and found that Ca²⁺ was able to partially restore the inhibition of seedling growth by Pb²⁺ and Zn²⁺.     

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.     

Compartments for the Management of Municipal Solid Waste

Despite technological developments and improved liner-material applications, heavy metals in landfill leachate still penetrate the soil profile, polluting the soil and ground-water. An alternative approach therefore must be explored to reduce heavy-metal migration in soil-bentonite landfill liners. By considering the interaction of different heavy metals and their synergetic and antagonistics behaviors, such an approach could be developed. Low mobility metals such as Cu²⁺, and Pb²⁺ inhibit the adsorption of Cd²⁺ which is a moderate-mobility metal and Cu²⁺ sorption is decreased by the presence of Zn²⁺ and Cd²⁺. Therefore, Zn²⁺, a low-mobility metal, cannot be grouped with Cu²⁺. This way, four compatible metal groups have been identified: (1) low mobility: Pb²⁺, Cu²⁺, and Ag, (2) low mobility: Zn²⁺ and Cr³⁺; (3) moderate mobility: As²⁺, Fe²⁺, and Ni²⁺; (4) high mobility: Cd²⁺ and Hg²⁺. Cd²⁺ with a moderate mobility pattern is synergetic to Fe²⁺ and is more mobile with Ni²⁺. Therefore, Cd²⁺ is separated from the moderate-mobility group and is consigned with Hg, a high-mobility metal. The liner materials suitable for Hg²⁺ are assumed to be suitable for Cd²⁺ as well. Based on this concept, and to reduce heavy metal mobility, wastes should be segregated on compatibility basis according to their heavy metal contents before being disposed in different individual compartments. For wastes containing several incompatible heavy metals, sorting should be based on the heavy-metal with the highest concentration. Another solution is the manufacturing of products using compatible heavy metal combinations and then labeling them accordingly. Such waste segregation and landfill compartmentalization lowers risks of groundwater contamination and liner cost.     

Activated carbon-containing alginate adsorbent for the simultaneous removal of heavy metals and toxic organics

By combining two functions of alginate gel and activated carbon, an activated carbon-containing alginate bead (AC-AB) adsorbent was developed and successfully used to simultaneously remove heavy metal ions and toxic organics. Quantitative analysis showed that almost all of the adsorption of toxic organics, such as p-toluic acid, is caused by the activated carbon in the AC-AB adsorbent, whereas the alginate component has a major role in the removal of heavy metals. A 50-L solution containing eight heavy metals (Pb²⁺, Mn²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Fe²⁺, Al³⁺ and Hg²⁺) and four mineral ions was run continuously through a filter cartridge packed with 160 g of the AC-AB adsorbent. The adsorbent showed a high capacity to remove heavy metals completely from the water, while allowing essential minerals, such as K⁺, Na⁺, Mg²⁺ and Ca²⁺, to pass through the filter. The adsorbent could be regenerated using eluents, such as HNO₃, and reused repeatedly without considerable loss of its metal uptake capacity through 10 subsequent cycles of adsorption and desorption. With its high capacity and high selectivity for toxic heavy metals, the AC-AB adsorbent has enormous potential for application in drinking water treatment technologies.     

Effect of heavy metals on the glutathione status in different ectomycorrhizal <Emphasis Type="Italic">Paxillus involutus</Emphasis> strains

The glutathione (GSH) status and heavy metal tolerance were investigated in four Paxillus involutus strains isolated from different heavy-metal-polluted and non-polluted regions of Europe. The heavy metal burden in the habitats did not affect significantly either the heavy metal (Cr₂O₇²⁻, Cd²⁺, Hg²⁺, Pb²⁺, Zn²⁺, Cu²⁺) tolerance and accumulation or the GSH production of the strains tested. Exposures to heavy metals increased the intracellular GSH concentrations in 12 from 24 experimental arrangements (four strains exposed to six heavy metals) independently of the habitats of the strains. The importance of GSH in heavy metal tolerance (high MIC values, ability to accumulate heavy metals and to grow in the presence of heavy metals) was thus demonstrated in this ectomycorrhizal fungus.     

Modulation of synaptic events by heavy metals in the central nervous system of mollusks

Summary 1. The effects of heavy metals (Pb²⁺, Hg²⁺, and Zn²⁺) on synaptic transmission in the identified neural network ofHelix pomatia L. andLymnaea stagnalis L. (Gastropoda, Mollusca) were studied, with investigation of effects on inputs and outputs as wells as on interneuronal connections.2. The sensory input running from the cardiorenal system to the central nervous system and the synaptic connections between central neurons were affected by heavy metals.3. Lead and mercury (10^–5–10^–3 M) eliminated first the inhibitory, then the excitatory inputs running from the heart to central neurons. At the onset of action lead increased the amplitude of the excitatory postsynaptic potentials, but blockade of sensory information transfer occurred after 10–20 min of treatment.4. The monosynaptic connections between identified interneurons were inhibited by lead and mercury but not by zinc. Motoneurons were found to be less sensitive to heavy metal treatment than interneurons or sensory pathways.5. The treatment with Pb²⁺ and Hg²⁺ often elicited pacemaker and bursting-type firing in central neurons, accompanied by disconnection of synaptic pathways, manifested by insensitivity to sensory synaptic influences.6. Zn²⁺ treatment also sometimes induced pacemaker activity and burst firing but did not cause disconnection of the synaptic transmission between interneurons.7. A network analysis of heavy metal effects can be a useful tool in understanding the connection between their cellular and their behavioral modulatory influences.     

Uptake of Metal Ions by Rhizopus arrhizus Biomass

Rhizopus arrhizus biomass was found to absorb a variety of different metal cations and anions but did not absorb alkali metal ions. The amount of uptake of the cations was directly related to ionic radii of La³⁺, Mn²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ba²⁺, Hg²⁺, Pb²⁺, UO₂²⁺, and Ag⁺. The uptake of all the cations is consistent with absorption of the metals by sites in the biomass containing phosphate, carboxylate, and other functional groups. The uptake of the molybdate and vanadate anions was strongly pH dependent, and it is proposed that the uptake mechanism involves electrostatic attraction to positively charged functional groups.     

Heavy Metals Modulate Glutamatergic System in Human Platelets

Research strategies have been developed to characterize parameters in peripheral tissues that might easily be measured in humans as surrogate markers of damage, dysfunction or interactions involving neural targets of toxicants. The similarities between platelet and neuron may even be clinically important, as a number of biochemical markers show parallel changes in the central nervous system (CNS) and platelets. The purpose of our research was to investigate the effect of Hg²⁺, Pb²⁺ and Cd²⁺ on the [³H]-glutamate binding and [³H]-glutamate uptake in human platelets. The involvement of oxidative stress in the modulation of glutamatergic system induced by heavy metals was also investigated. The present study clearly demonstrates that Hg²⁺, Cd²⁺, and Pb²⁺ inhibited [³H]-glutamate uptake in human platelets. Hg²⁺ inhibited [³H]-glutamate binding, while Cd²⁺ and Pb²⁺ stimulated [³H]-glutamate binding in human platelets. Hg²⁺, Cd²⁺ and Pb²⁺ increased lipid peroxidation levels and reactive oxygen species (ROS) measurement in platelets. The present limited results could suggest that glutamatergic system may be used as a potential biomarker for neurotoxic action of heavy metals in humans.     

Modulation of Na+ transport across leech skin by pesticides and heavy metals

The aim of the present study was to investigate the effects of environmental pollutants, such as heavy metals and pesticides on ion transport across the skin of the leech (Hirudo medicinalis). We wanted to examine the suitability of this epithelium as a model system for studies concerning the mechanisms of toxic action caused by environmental pollutants. For this purpose we performed Ussing chamber experiments to test three representative heavy metals and pesticides, respectively, for their effects on current flow across leech dorsal integument. Two representatives of each substance class showed distinct effects on ion transport across this epithelium. The heavy metal ions Pb²⁺ and Hg²⁺ produced a significant inhibition of amiloride-sensitive Na⁺ transport across leech skin in concentrations below or close to their limiting values in waste water. Therefore, it seems feasible to use leech skin for future investigations of the toxic actions of these heavy metals. The fact that Pb²⁺ and Hg²⁺ exerted their effects only when applied apically points to a specific action of these divalent cations on ion channels in the apical membrane. However, this inhibition does not seem to be a general feature of divalent cations because Cd²⁺ did not influence ion transport across leech skin at all. Since current flow through amiloride-sensitive Na⁺ channels in typical vertebrate tight epithelia is stimulated by numerous divalent cations, the pronounced inhibition of amiloride-sensitive Na⁺ channels in leech skin by Pb²⁺ and Hg²⁺ might lead to a further differentiation of amiloride-sensitive Na⁺ channels. The two widespread pesticides lindane and promecarb exerted their effects only at comparativ high concentrations. This low sensitivity restricts the usefulness of leech skin as a subject for further analysis of toxicity mechanisms, at least for these two pesticides.     

细胞内离子在气孔运动中的作用

气孔运动与植物水分代谢密切相关。保卫细胞中的无机离子作为第二信使(Ca²⁺)或者渗透调节物质(K⁺、Cl^–)在响应 外界理化因子的刺激、调节保卫细胞膨压过程中发挥重要作用。保卫细胞质膜和液泡膜上的离子通道作为各种刺激因素作 用的靶位点, 是保卫细胞离子转运的关键组分, 在气孔运动调控过程中扮演关键角色。该文对近年来保卫细胞离子的作用 和离子通道研究的进展进行了综述。     

Comparison of Physiological Changes in Euglena gracilis During Exposure to Heavy Metals of Heterotrophic and Autotrophic Cells

The effect of different concentrations of Hg²⁺, Cd²⁺, and Pb²⁺ on ultrastructure, growth, respiration, photosynthesis, chlorophyll content, and metal accumulation in Euglena gracilis was examined. The toxicity of the heavy metals was dependent on the culture medium used and whether cells were grown in the dark or under illumination. Hg²⁺ was the most toxic metal, which showed effects at a concentration as low as 1.5 μM; Cd²⁺ showed an intermediate toxicity (effects observed above 50 μM); and Pb²⁺ was almost ineffective up to 1 mM. Cells grown for several weeks in the dark, in the presence of 1.5 μM Hg²⁺ showed a reduced sensitivity to subsequent exposure to Cd²⁺ or Pb²⁺. The Hg²⁺-pretreated cells also presented an enhanced capacity to accumulate other metals. In comparison, light-grown cells showed a greater Cd²⁺ accumulation, but a lower Pb²⁺ uptake than Hg²⁺-pretreated dark-grown cells. Pretreatment of light-grown cells with Hg²⁺ did not enhance the accumulation of Cd²⁺. These results suggest that the capacity to tolerate heavy metals by Euglena may have mechanistic differences when cells are grown in the dark or under illumination.     

Distinct responses to ozone of abaxial and adaxial stomata in three Euramerican poplar genotypes

Ozone induces stomatal sluggishness, which impacts photosynthesis and transpiration. Stomatal responses to variation of environmental parameters are slowed and reduced by ozone and may be linked to difference of ozone sensitivity. Here we determine the ozone effects on stomatal conductance of each leaf surface. Potential causes of this sluggish movement, such as ultrastructural or ionic fluxes modification, were studied independently on both leaf surfaces of three Euramerican poplar genotypes differing in ozone sensitivity and in stomatal behaviour. The element contents in guard cells were linked to the gene expression of ion channels and transporters involved in stomatal movements, directly in microdissected stomata. In response to ozone, we found a decrease in the stomatal conductance of the leaf adaxial surface correlated with high calcium content in guard cells compared with a slight decrease on the abaxial surface. No ultrastructural modifications of stomata were shown except an increase in the number of mitochondria. The expression of vacuolar H⁺/Ca²⁺‐antiports (CAX1 and CAX3 homologs), β‐carbonic anhydrases (βCA1 and βCA4) and proton H⁺‐ATPase (AHA11) genes was strongly decreased under ozone treatment. The sensitive genotype characterized by constitutive slow stomatal response was also characterized by constitutive low expression of genes encoding vacuolar H⁺/Ca²⁺‐antiports.     

沉水植物菹草在低温条件下对重金属Cu、Pb、Zn的吸附和富集

在10℃的较低温度条件下,研究了冬春季节生长旺盛的沉水植物菹草(Potamogeton crispus L.)对重金属离子Cu²⁺,Pb²⁺,Zn²⁺的生物吸附特征及解吸情况,对不同初始浓度重金属水体中的重金属离子去除率情况,以及在此过程中菹草各器官(叶、茎、根茎、根)对重金属离子的富集情况。结果表明,菹草对Cu²⁺,Zn²⁺的吸附在20 min内达到平衡,对Pb²⁺的吸附在50 min内达到平衡,吸附动力学结果符合伪二级动力学方程,决定系数分别达1,1,0.997 8。Freundlich等温线可较好地拟合菹草吸附Cu²⁺,Pb²⁺,Zn²⁺的过程,Cu²⁺,Pb²⁺,Zn²⁺的吸附容量分别达到66.900 6,26.543 0,30.371 8 mg·L^-1。以去离子水作洗脱剂,解吸液中3种重金属离子浓度均低于仪器检出限(0.01 mg·L^-1),解吸程度微弱。投放菹草后,随着初始处理浓度的升高,水体Cu²⁺的去除率先降低后升高,Pb²⁺的去除率的变化趋势与Cu²⁺类似。Zn²⁺去除率则随水体Zn²⁺初始浓度的升高而逐渐升高。菹草各器官对水体3种重金属离子的富集能力不同,排序为Cu²⁺＞Zn²⁺＞Pb²⁺。不同器官对同一种重金属离子的富集量差异显著,叶是富集重金属离子的主要器官。水体重金属离子的初始浓度会影响菹草各器官富集重金属离子的能力,一般随水体重金属初始浓度升高,菹草各器官的重金属离子富集量虽有不同程度的增加但富集系数持续减小。     

Inhibition of Na+/K+-ATPase and Mg2+-ATPase by metal ions and prevention and recovery of inhibited activities by chelators

Kinetics and inhibition of Na⁺/K⁺-ATPase and Mg²⁺-ATPase activity from rat synaptic plasma membrane (SPM), by separate and simultaneous exposure to transition (Cu²⁺, Zn²⁺, Fe²⁺ and.Co²⁺) and heavy metals (Hg²⁺and Pb²⁺) ions were studied. All investigated metals produced a larger maximum inhibition of Na⁺/K⁺-ATPase than Mg²⁺-ATPase activity. The free concentrations of the key species (inhibitor, MgATP^{2 ?} , MeATP^{2 ?} ) in the medium assay were calculated and discussed. Simultaneous exposure to the combinations Cu²⁺/Fe²⁺ or Hg²⁺/Pb²⁺caused additive inhibition, while Cu²⁺/Zn²⁺ or Fe²⁺/Zn²⁺ inhibited Na⁺/K⁺-ATPase activity synergistically (i.e., greater than the sum metal-induced inhibition assayed separately). Simultaneous exposure to Cu²⁺/Fe²⁺ or Cu²⁺/Zn²⁺ inhibited Mg²⁺-ATPase activity synergistically, while Hg²⁺/Pb²⁺ or Fe²⁺/Zn²⁺ induced antagonistic inhibition of this enzyme. Kinetic analysis showed that all investigated metals inhibited Na⁺/K⁺-ATPase activity by reducing the maximum velocities (V_max) rather than the apparent affinity (K_m) for substrate MgATP^2-, implying the noncompetitive nature of the inhibition. The incomplete inhibition of Mg²⁺-ATPase activity by Zn²⁺, Fe²⁺ and Co²⁺ as well as kinetic analysis indicated two distinct Mg²⁺-ATPase subtypes activated in the presence of low and high MgATP^{2 ?} concentration. EDTA, L-cysteine and gluthathione (GSH) prevented metal ion-induced inhibition of Na⁺/K⁺-ATPase with various potencies. Furthermore, these ligands also reversed Na⁺/K⁺-ATPase activity inhibited by transition metals in a concentration-dependent manner, but a recovery effect by any ligand on Hg²⁺-induced inhibition was not obtained.     

Heavy metal ion inhibition studies of human,sheep and fish α-carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) were purified from sheep kidney (sCA IV), from the liver of the teleost fish Dicentrarchus labrax (dCA) and from human erythrocytes (hCA I and hCA II). The purification procedure consisted of a single step affinity chromatography on Sepharose 4B-tyrosine-sulfanilamide. The kinetic parameters of these enzymes were determined for their esterase activity with 4-nitrophenyl acetate as substrate. The following metal ions, Pb²⁺, Co²⁺, Hg²⁺, Cd²⁺, Zn²⁺, Se²⁺, Cu²⁺, Al³⁺ and Mn³⁺ showed inhibitory effects on these enzymes. The tested metal ions inhibited these CAs competitively in the low milimolar/submillimolar range. The susceptibility to various cations inhibitors differs significantly between these vertebrate α-CAs and is probably due to their binding to His64 or the histidine cluster.     

Isolation and Molecular Characterization of Heavy Metal-Resistant Azotobacter chroococcum from Agricultural Soil and Their Potential Application in Bioremediation

Pollution of soil with heavy metals, herbicides, antibiotics and other chemicals is known to have a negative effect on microbial activities. Therefore, the aim of this study was to isolate cultures of Azotobacter sp. from polluted and unpolluted soils and to study the effect of these pollutants on their growth. A total of 120 Azotobacter sp. were isolated from soils irrigated with wastewater (contaminated soils) and groundwater (uncontaminated soils). These isolates were screened for resistance to heavy metals, herbicide and antibiotics. Also, the soils from which the cultures were isolated were analyzed for the concentrations of Zn²⁺, Cd²⁺, Cu²⁺, Pb²⁺ and Mn²⁺ they contained. Contaminated soil showed high levels of heavy metals as compared to uncontaminated soil. The size of the Azotobacter population in contaminated soil was lower than that in uncontaminated soil. Of the Azotobacter isolates, 64 that were recovered from contaminated soil exhibited high resistance to heavy metals (Hg²⁺, Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺ and Pb²⁺) and herbicide 2,4-D compared to 56 isolates from uncontaminated soil. Also, isolates from contaminated soil showed high resistance to chloramphenicol, nitrofurantoin and co-trimoxazole compared to those isolated from uncontaminated soil. The majority of Azotobacter isolates from contaminated soil showed multiple-resistance to different metal ions and antibiotics. All isolates failed to grow at pH less than 6. Salt concentration (5%) was found to be inhibitory to all isolates. The most potent isolates from contaminated soil that showed multiresistance to all substances tested were identified on the basis of morphological and biochemical characteristics, and 16S rRNA as A. chroococcum. These resistant isolates could be employed in contaminated soils and/or bioremediation.     

Effects of heavy metal cations on the mitochondrial ornithine/citrulline transporter reconstituted in liposomes

The effect of heavy metal cations on the mitochondrial ornithine/citrulline transporter was tested in proteoliposomes reconstituted with the protein purified from rat liver. The transport activity was measured as [³H]ornithine uptake in proteoliposomes containing internal ornithine (ornithine/ornithine antiport mode) or as [³H]ornithine efflux in the absence of external substrate (ornithine/H⁺ transport mode). 0.1 mM Cu²⁺, Pb²⁺, Hg²⁺, Cd²⁺ and Zn²⁺ strongly inhibited (more than 85%) the antiport; whereas Mn²⁺, Co²⁺ and Ni²⁺ inhibited less efficiently (25, 47 and 69%, respectively). The IC₅₀ values of the transporter for the different metal ions ranged from 0.71 to 350 μM. Co²⁺ and Ni²⁺ also inhibited the [³H]ornithine efflux whereas Cu²⁺, Pb²⁺, Hg²⁺, Cd²⁺ and Zn²⁺ stimulated the [³H]ornithine efflux. The stimulation of the [³H]ornithine efflux by Cu²⁺ and Cd²⁺ (as well as by Pb²⁺, Hg²⁺ and Zn²⁺) was not prevented by NEM and was reversed by DTE. These features indicated that the inhibition of the antiport was due to the interaction of the Cu²⁺, Pb²⁺, Hg²⁺, Cd²⁺ and Zn²⁺ with a population of SH groups, of the transporter, responsible for the inhibition of the physiological function; whereas the stimulation of [³H]ornithine efflux was due to the induction of a pore-like function of the transporter caused by interaction of cations with a different population of SH groups. Differently, the inhibition of the ornithine transporter by Ni²⁺, Co²⁺ or Mn²⁺ was caused by interaction with the substrate binding site, as indicated by the competitive or mixed inhibition.