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1.
Pollution by copper (Cu 2+) extensively used as antimicrobial in agriculture and farming represents a threat to the environment and human health. Finding ways to make microorganisms sensitive to lower metal concentrations could help decreasing the use of Cu 2+ in agriculture. In this respect, we showed that limiting iron (Fe) uptake makes bacteria much more susceptible to Cu 2+ or Cd 2+ poisoning. Using efflux mutants of the purple bacterium Rubrivivax gelatinosus, we showed that Cu + and Cd 2+ resistance relies on the expression of the Fur-regulated FbpABC and Ftr iron transporters. To support this conclusion, inactivation of these Fe-importers in the Cu + or Cd 2+-ATPase efflux mutants gave rise to hypersensitivity towards these ions. Moreover, in metal overloaded cells the expression of FbpA, the periplasmic iron-binding component of the ferric ion transport FbpABC system was induced, suggesting that cells perceived an ‘iron-starvation’ situation and responded to it by inducing Fe-importers. In this context, the Fe-Sod activity increased in response to Fe homoeostasis dysregulation. Similar results were obtained for Vibrio cholerae and Escherichia coli, suggesting that perturbation of Fe-homoeostasis by metal excess appeared as an adaptive response commonly used by a variety of bacteria. The presented data support a model in which metal excess induces Fe-uptake to support [4Fe-4S] synthesis and thereby induce ROS detoxification system. 相似文献
2.
Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag+, AsO
−2
, AsO
3−4
, Cd2+, Co2+, CrO
2−4
, Cu2+, Hg2+, Ni2+, Pb2+, TeO
2−3
, Tl+ and Zn2+. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd2+-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd2+, Zn2+, and Co2), others are known that efflux Ag+, Cu+, Ni2+, and Zn2+. Resistance to inorganic mercury, Hg2+ (and to organomercurials, such as CH3Hg+ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite. 相似文献
3.
A metallothionein-like gene, ThMT3, encoding a type 3 metallothionein, was isolated from a Tamarix hispida leaf cDNA library. Expression analysis revealed that mRNA of ThMT3 was upregulated by high salinity as well as by heavy metal ions, and that ThMT3 was predominantly expressed in the leaf. Transgenic yeast ( Saccharomyces cerevisiae) expressing ThMT3 showed increased tolerance to Cd 2+, Zn 2+, Cu 2+, and NaCl stress. Transgenic yeast also accumulated more Cd 2+, Zn 2+, and NaCl, but not Cu 2+. Analysis of the expression of four genes ( GLR1, GTT2, GSH1, and YCF1) that aid in transporting heavy metal (Cd 2+) from the cytoplasm to the vacuole demonstrated that none of these genes were induced under Cd 2+, Zn 2+, Cu 2+, and NaCl stress in ThMT3-transgenic yeast. H 2O 2 levels in transgenic yeast under such stress conditions were less than half those in control yeast under the same conditions.
Three antioxidant genes ( SOD1, CAT1, and GPX1) were specifically expressed under Cd 2+, Zn 2+, Cu 2+, and NaCl stress in the transgenic yeast. Cd 2+, Zn 2+, and Cu 2+ increased the expression levels of SOD1, CAT1, and GPX1, respectively, whereas NaCl induced the expression of SOD1 and GPX1. 相似文献
4.
Metallothioneins (MTs) are low-molecular-weight proteins with high Cys content and high metal-chelating ability. CdMT and CuMT subfamilies present different characteristics in Tetrahymena. To explore the effect of the cysteine arrangement and sequence length of MTs for binding different metal ions, MTT1, truncated MTT1 ( TM1), MTT2, and truncated MTT2 (TM2) were expressed in E. coli. The half-maximal inhibiting concentrations (IC 50) of Cd 2+ and Cu + for the recombinant strains were different. Furthermore, E. coli cells expressing MTT1 and TM1 exhibited higher accumulating ability for Cd 2+ than cells expressing MTT2 and TM2. However, the opposite is true for Cu +. The binding ability of the different recombinant proteins to Cd 2+ and Cu + were also different. MTT1 and truncated mutant TM1 were the preference for Cd 2+, whereas MTT2 and truncated mutant TM2 were the preference for Cu + coordination. These results showed that metal ion tolerance and accumulation ability not only depended on cysteine arrangement pattern but also on sequence length of MT in Tetrahymena. 相似文献
5.
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 Cd 2+, Cu 2+, Zn 2+, 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. IC 50 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 Cd 2+ and Cu 2+ were non‐competitive, whereas Zn 2+ and Ag + were competitive. Co 2+, Cr 2+, Pb 2+, and Fe 3+ had no inhibitory activity on GST. 相似文献
6.
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 (Cd 2+, Cu 2+, Pb 2+, and Zn 2+) in aqueous solution. The humid T. fuciformis showed the highest capacity to adsorb the four metals in the multi-metal solutions. The Pb 2+ 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 Pb 2+ by dried and humid T. fuciformis in Cd 2+ + Pb 2+, Cu 2+ + Pb 2+, Pb 2+ + Zn 2+, Cd 2+ + Cu 2+ + Pb 2+, and Cd 2+ + Zn 2+ + Pb 2+ solutions were not lower than that in Pb 2+ solutions. The results suggested that in humid T. fuciformis, Cd 2+, Cu 2+, and Zn 2+ promoted the Pb 2+ adsorption by the biomass. In the multi-metal solutions of Cd 2+ + Cu 2+ + Pb 2+ + Zn 2+, the adsorption amount and rates of the metals by all the test biosorbents were in the order of Pb 2+ > Cu 2+ > Zn 2+ > Cd 2+. 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 Cd 2+, Cu 2+, Pb 2+, and Zn 2+. 相似文献
7.
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 Cu 2+, Pb 2+, Hg 2+, Cd 2+ and Zn 2+ strongly inhibited (more than 85%) the antiport; whereas Mn 2+, Co 2+ and Ni 2+ inhibited less efficiently (25, 47 and 69%, respectively). The IC 50 values of the transporter for the different metal ions ranged from 0.71 to 350 μM. Co 2+ and Ni 2+ also inhibited the [ 3H]ornithine efflux whereas Cu 2+, Pb 2+, Hg 2+, Cd 2+ and Zn 2+ stimulated the [ 3H]ornithine efflux. The stimulation of the [ 3H]ornithine efflux by Cu 2+ and Cd 2+ (as well as by Pb 2+, Hg 2+ and Zn 2+) 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 Cu 2+, Pb 2+, Hg 2+, Cd 2+ and Zn 2+ 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 Ni 2+, Co 2+ or Mn 2+ was caused by interaction with the substrate binding site, as indicated by the competitive or mixed inhibition. 相似文献
8.
Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH 4
+, K +, Mg 2+, Co 2+, Fe 3+, Mn 2+, Zn 2+ and other trace cations, PO 4
3-, SO 4
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 + AsO 2
-, AsO 4
3-, Cd 2+, Co 2+, CrO 4
2−, Cu 2+, Hg 2+, Ni 2+, Pb 2+, TeO 3
2−, TI + and Zn 2+. 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 Cd 2+-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 Cd 2+ (and Zn 2+) 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 Cd 2+, Zn 2+ and Co 2+. 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 相似文献
9.
为了探讨重金属Cd 2+和Cu 2+胁迫对泥蚶消化酶活性的影响,运用酶学分析的方法,按《渔业水质标准》(GB 11607)规定的Cd 2+、Cu 2+最高限量值的1、2、5、10倍设置重金属离子Cd 2+、Cu 2+浓度及其组合,研究了在重金属Cd 2+、Cu 2+胁迫下,30d内泥蚶3种消化酶活性的变化规律。结果表明:与空白对照组相比,在重金属Cd 2+、Cu 2+或其组合的胁迫下,较低浓度组泥蚶的淀粉酶活性实验前期增强(即被诱导),实验后期减弱(即被抑制),较高浓度组泥蚶的淀粉酶活性从实验一开始就减弱,并保持在较低水平,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合Cu 2+ > (Cd 2++Cu 2+)组合 > Cd 2+;泥蚶脂肪酶的活性实验前期增强,实验后期转为微减弱或减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合(Cd 2++Cu 2+)组合 > Cu 2+ > Cd 2+;泥蚶胃蛋白酶的活性实验前期增强,且活性呈现升高-降低-再升高-再降低的变化,实验后期分别表现微增强、微减弱和减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合(Cd 2++Cu 2+)组合 > Cu 2+ > Cd 2+。可见:环境中的Cd 2+和Cu 2+对泥蚶的消化酶活性起着明显的影响作用。 相似文献
10.
Bacterial plasmids encode resistance systems for toxic metal ions, including Ag +, AsO 2-, AsO 43-, Cd 2+, Co 2+, CrO 42-, Cu 2+ Hg 2+, Ni 2+, Pb 2+, Sb 3+, TeO 32-, Tl + and Zn 2+. The function of most resistance systems is based on the energy-dependent efflux of toxic ions. Some of the efflux systems are ATPases and others are chemiosmotic cation/proton antiporters. The Cd 2+-resistance ATPase of Gram-positive bacteria (CadA) is membrane cation pump homologous with other bacterial, animal and plant P-type ATPases. CadA has been labeled with 32P from [ α- 32p]ATP and drives ATP-dependent Cd 2+ (and Zn 2+) uptake by inside-out membrane vesicles (equivalent to efflux from whole cells). Recently, isolated genes defective in the human hereditary diseases of copper metabolism, namely Menkes syndrome and Wilson's disease, encode P-type ATPases that are more similar to bacterial CadA than to other ATPases from eukaryotes. The arsenic resistance efflux system transports arsenite [As(III)], alternatively using either a double-polypeptide (ArsA and ArsB) ATPase or a single-polypeptide (ArsB) functioning as a chemiosmotic transporter. The third gene in the arsenic resistance system, arsC, encodes an enzyme that converts intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. The triple-polypeptide Czc (Cd 2+, Zn 2+ and Co 2+) chemiosmotic efflux pump consists of inner membrane (CzcA), outer membrane (CzcC) and membrane-spanning (CzcB) proteins that together transport cations from the cytoplasm across the periplasmic space to the outside of the cell. 相似文献
11.
The effects of some metal ions on amidolytic and fibrinogenolytic activities of highly purified human plasmin were investigated
in vitro. In the presence of Zn 2+, Cu 2+, Cd 2+, and Au + in the incubation mixture at the concentrations of 1×10 −5−1×10 −3
M, the anidolytic plasmin activity was strongly inhibited, whereas Ca 2+ and Mg 2+ at the same concentrations were not effective. The analysis of the kinetic study has shown that Zn 2+ or Cu 2+ acts as mixed-type inhibitors of plasmin activity. The inhibition of amidolytic plasmin activity by Zn 2+ and Cu 2+ was reduced in the presence of EDTA, histidine, or albumin. Incubation of plasmin with Zn 2+ or Cu 2+ (at the concentration of 5×10 −4
M) resulted in complete loss of its proteolytic action on fibrinogen, whereas Cd 2+ and Au + under the same conditions only partially inhibited this process. 相似文献
12.
In liver homogenate the biosynthesis of N-acetylneuraminic acid using N-acetylglucosamine as precursor can be followed stepwise by applying different chromatographic procedures. In this cell-free system 16 metal ions (Zn 2+, Mn 2+, La 3+, Co 2+, Cu 2+, Hg 2+, VO
3
–
, Pb 2+, Ce 3+, Cd 2+, Fe 2+, Fe 3+, Al 3+, Sn 2+, Cs + and Li +) and the selenium compounds, selenium(IV) oxide and sodium selenite, have been checked with respect to their ability to influence a single or possible several steps of the biosynthesis of N-acetylneuraminic acid. It could be shown that the following enzymes are sensitive to these metal ions (usually applied at a concentration of 1 mmoll –1): N-acetylglucosamine kinase (inhibited by Zn 2+ and vandate), UDP- N-acetylglucosamine-2-epimerase (inhibited by zn 2+, Co 2+, Cu 2+, Hg 2+, VO
3
–
, Pb 2+, Cd 2+, Fe 3+, Cs +, Li +, selenium(IV) oxide and selenite), and N-acetylmannosamine kinase (inhibited by Zn 2+, Cu 2+, Cd 2+, and Co 2+). Dose dependent measurements have shown that Zn 2+, Cu 2+ and selenite are more efficient inhibitors of UDP- N-acetylglucosamine-2-epimerase than vanadate. As for the N-acetylmannosamine kinase inhibition, a decreasing inhibitory effect exists in the following order Zn 2+, Cd 2+, Co 2+ and Cu 2+. In contrast, La 3+, Al 3+ and Mn 2+ (1 mmoll –1) did not interfere with the biosynthesis of N-acetylneuraminic acid. Thus, the conclusion that the inhibitory effect of the metal ions investigated cannot be regarded as simply unspecific is justified.Dedicated to Professor Theodor Günther on the occasion of his 60th birthday 相似文献
13.
Cu +-ATPases play a key role in bacterial Cu + homeostasis by participating in Cu + detoxification and cuproprotein assembly. Characterization of Archaeoglobus fulgidus CopA, a model protein within the subfamily of P 1B-1 type ATPases, has provided structural and mechanistic details on this group of transporters. Atomic resolution structures
of cytoplasmic regulatory metal binding domains (MBDs) and catalytic actuator, phosphorylation, and nucleotide binding domains
are available. These, in combination with whole protein structures resulting from cryo-electron microscopy analyses, have
enabled the initial modeling of these transporters. Invariant residues in helixes 6, 7 and 8 form two transmembrane metal
binding sites (TM-MBSs). These bind Cu + with high affinity in a trigonal planar geometry. The cytoplasmic Cu + chaperone CopZ transfers the metal directly to the TM-MBSs; however, loading both of the TM-MBSs requires binding of nucleotides
to the enzyme. In agreement with the classical transport mechanism of P-type ATPases, occupancy of both transmembrane sites
by cytoplasmic Cu + is a requirement for enzyme phosphorylation and subsequent transport into the periplasmic or extracellular milieus. Recent
transport studies have shown that all Cu +-ATPases drive cytoplasmic Cu + efflux, albeit with quite different transport rates in tune with their various physiological roles. Archetypical Cu +-efflux pumps responsible for Cu + tolerance, like the Escherichia coli CopA, have turnover rates ten times higher than those involved in cuproprotein assembly (or alternative functions). This
explains the incapability of the latter group to significantly contribute to the metal efflux required for survival in high
copper environments. 相似文献
14.
Complexes formed by reduced glutathione (GSH) with metal cations (Cr 2+, Mn 2+,Fe 2+,Co 2+,Ni 2+,Cu 2+,Zn 2+,Cd 2+,Hg 2+) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu 2+>Ni 2+>Co 2+>Fe 2+>Cr 2+>Zn 2+>Mn 2+; and for the same group of metal ions, the general trend of binding energies was Zn 2+>Hg 2+>Cd 2+. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe 2+,Co 2+,Ni 2+,Cu 2+,Zn 2+,Cd 2+ and Hg 2+ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr 2+ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu 2+, Ni 2+,Co 2+ and Hg 2+ had obvious tendencies to be reduced to Cu +,Ni +,Co + and Hg + during the coordination process. 相似文献
15.
Summary The alga, Distigma proteus, isolated from industrial wastewater showed tolerance against Cd 2+ (8.0 μg/ml), Cr 6+ (12 μg/ml), Pb 2+ (15 μg/ml) and Cu 2+ (10 μg/ml). The metal ions slowed down the growth of the organism after 4–5 days of exposure. The reduction in cell population
was 90% for Cu 2+, 84% for Cd 2+, 71% for Cr 6+, and 63% for Pb 2+ after 8 days of metal stress. The order of resistance to heavy metal, in terms of reduction in the cellular population, was
Cu 2+ > Cd 2+ > Cr 6+ > Pb 2+. Chromium- and cadmium-processing capabilities of the alga were worked out for its potential use as a bioremediator of wastewater.
The reduction in the amount of Cr 6+ after 2, 4, 6 and 8 days of algal culture containing 5.0 μg Cr 6+ ml −1 of culture medium was 77, 85, 92 and 97%, respectively. Distigma could also remove 48% Cd 2+after 2 days, 68% after 4 days, 80% after 6 days and 90% after 8 days from the medium. The heavy metal uptake ability of Distigma can be exploited for metal detoxification and environmental clean-up operations. 相似文献
16.
The plasmalemma vesicles isolated from cucumber and maize roots were used to study the effect of Cu 2+ and Cd 2+ on the hydrolytic and proton pumping activities of ATPase. In vivo application of metal ions to the plant growth solutions resulted in stimulation of the proton transport in maize. In cucumber
roots the action of metals was not the same: cadmium stimulated the H + transport through plasmalemma whereas Cu 2+ almost completely inhibited it. Copper ions decreased the hydrolytic activity of H +-ATPase in cucumber, without any effect on this activity in membranes isolated from maize roots. The effect of cadmium on
the hydrolytic activities was opposite: ATP-hydrolysis activity in plasmalemma was not altered in cucumber, whereas in maize
its stimulation was observed. The amount of accumulated metals was not the main reason of different influence of metals on
H +-ATPase activity in tested plants. In in vitro experiments Cu 2+ inhibited H + transport in the cucumber, to a higher degree than Cd 2+ and both metals did not change this H +-ATPase activity of plasmalemma isolated from corn roots. Cu 2+ added into the incubation medium reduced the hydrolytic activity of ATPase in the plasma membrane isolated from cucumber
as well as from corn roots. Cd 2+ diminished the hydrolytic activity of ATPase in cucumber, and no effect of Cd 2+ in the plasmalemma isolated from corn roots was found. Our results indicated different in vitro and in vivo action of both metals on H +-ATPase and different response of this enzyme to Cu 2+ and Cd 2+ in maize and cucumber. 相似文献
17.
Zn 2+‐responsive repressor ZiaR and Co 2+‐responsive activator CoaR modulate production of P 1‐type Zn 2+‐ (ZiaA) and Co 2+‐ (CoaT) ATPases respectively. What dictates metal selectivity? We show that Δ ziaΔ coa double mutants had similar Zn 2+ resistance to Δ zia single mutants and similar Co 2+ resistance to Δ coa single mutants. Controlling either ziaA or coaT with opposing regulators restored no resistance to metals sensed by the regulators, but coincident replacement of the deduced cytosolic amino‐terminal domain CoaT N with ZiaA N (in ziaR‐ p ziaA‐ ziaANcoaT) conferred Zn 2+ resistance to Δ ziaΔ coa, Zn 2+ content was lowered and residual Co 2+ resistance lost. Metal‐dependent molar absorptivity under anaerobic conditions revealed that purified ZiaA N binds Co 2+ in a pseudotetrahedral two‐thiol site, and Co 2+ was displaced by Zn 2+. Thus, the amino‐terminal domain of ZiaA inverts the metals exported by zinc‐regulated CoaT from Co 2+ to Zn 2+, and this correlates simplistically with metal‐binding preferences; KZiaAN Zn 2+ tighter than Co 2+. However, Zn 2+ did not bleach Cu +‐ZiaA N, and only Cu + co‐migrated with ZiaA N after competitive binding versus Zn 2+. Bacterial two‐hybrid assays that detected interaction between the Cu +‐metallochaperone Atx1 and the amino‐terminal domain of Cu +‐transporter PacS N detected no interaction with the analogous, deduced, ferredoxin‐fold subdomain of ZiaA N. Provided that there is no freely exchangeable cytosolic Cu +, restricted contact with the Cu +‐metallochaperone can impose a barrier impairing the formation of otherwise favoured Cu +–ZiaA N complexes. 相似文献
18.
Biochemical responses to cadmium (Cd 2+) and copper (Cu 2+) exposure were compared in two strains of the aquatic hyphomycete (AQH) Heliscus lugdunensis. One strain (H4-2-4) had been isolated from a heavy metal polluted site, the other (H8-2-1) from a moderately polluted habitat.
Conidia of the two strains differed in shape and size. Intracellular accumulation of Cd 2+ and Cu 2+ was lower in H4-2-4 than in H8-2-1. Both␣strains synthesized significantly more glutathione (GSH), cysteine (Cys) and γ-glutamylcysteine
(γ-EC) in the presence of 25 and 50 μM Cd 2+, but quantities and rates of synthesis were different. In H4-2-4, exposure to 50 μM Cd 2+ increased GSH levels to 262% of the control; in H8-2-1 it increased to 156%. Mycelia of the two strains were analysed for
peroxidase, dehydroascorbate reductase, glutathione reductase and glucose-6-phosphate dehydrogenase. With Cd 2+ exposure, peroxidase activity increased in both strains. Cu 2+ stress increased dehydroascorbate reductase activity in H4-2-4 but not in H8-2-1. Dehydroascorbate reductase and glucose-6-phosphate
dehydrogenase activities progressively declined in the presence of Cd 2+, indicating a correlation with Cd 2+ accumulation in both strains. Cd 2+ and Cu 2+ exposure decreased glutathione reductase activity. 相似文献
19.
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 Al 3+, Ni 2+, Co 2+, Cd 2+, Cu 2+, Zn 2+, and Fe 2+ in Tris-HCl buffer and by Cd 2+, Zn 2+, Cu 2+, and Fe 2+ in potassium phosphate buffer. Fpg and Nei, the prokaryotic homologs of NEIL1, were inhibited by the same metal ions as NEIL1.
The values of I 50 for NEIL1 inhibition were 7 μM for Cd 2+, 16 μM for Zn 2+, and 400 μM for Cu 2+. The inhibition of NEIL1 by Cd 2+, Zn 2+, and Cu 2+ was at least partly due to the formation of metal-DNA complexes. In the case of Cd 2+ and Cu 2+, 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. 相似文献
20.
Among other detrimental effects of the heavy metal Cd 2+, a decrease in the plant content of essential mineral nutrients is known. In this study, the effect of Cd 2+ on different physiological activities of rice roots involved in nutrient acquisition has been studied. Upon addition of 0.1 or 1 mM Cd 2+ to the experimental solution, root cell membranes depolarized in few minutes, reaching very low Em values. This effect was transient and the initial membrane potential recovered totally within 6–8 h. Only the highest concentration used had an inhibitory effect on root respiration. Significant respiratory inhibition appeared after 2 h of exposure to Cd 2+ and lasted for at least 4 h. In turn, membrane permeability increased in the presence of Cd 2+ for at least 8 h, inducing K + efflux from the roots. The relationship between these parameters and their possible involvement in lowered nutrient content in Cd 2+-treated plants is discussed. 相似文献
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