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1.
Heavy metal contamination is a serious environmental problem. Understanding the toxicity mechanisms may allow to lower concentration of metals in the metal-based antimicrobial treatments of crops, and reduce metal content in soil and groundwater. Here, we investigate the interplay between metal efflux systems and the superoxide dismutase (SOD) in the purple bacterium Rubrivivax gelatinosus and other bacteria through analysis of the impact of metal accumulation. Exposure of the Cd 2+-efflux mutant Δ cadA to Cd 2+ caused an increase in the amount and activity of the cytosolic Fe-Sod SodB, thereby suggesting a role of SodB in the protection against Cd 2+. In support of this conclusion, inactivation of sodB gene in the Δ cadA cells alleviated detoxification of superoxide and enhanced Cd 2+ toxicity. Similar findings were described in the Cu +-efflux mutant with Cu +. Induction of the Mn-Sod or Fe-Sod in response to metals in other bacteria, including Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida, Vibrio cholera and Bacillus subtilis, was also shown. Both excess Cd 2+ or Cu + and superoxide can damage [4Fe-4S] clusters. The additive effect of metal and superoxide on the [4Fe-4S] could therefore explain the hypersensitive phenotype in mutants lacking SOD and the efflux ATPase. These findings underscore that ROS defence system becomes decisive for bacterial survival under metal excess. 相似文献
2.
Possible roles of cell wall and cytoplasmic peptides in the tolerance of cells to Cu 2+ and Cd 2+ ions were studied in suspension-cultured cells of tomato ( Lycopersicon esculentum L. cv. Palace). Cu 2+ and Cd 2+ ions inhibited growth of wild type cells at concentrations more than 100 and 200 μM, respectively. Tomato cells readily developed
tolerance to Cd 2+ ions up to 1 mM but not to Cu 2+ ions, after repeated subculturings in the presence of the respective ions. Such a metal-specific adaptation of cells was
not due to the difference in the total uptakes between Cd 2+ and Cu 2+ ions by cells. Wild-type cells accumulated Cd 2+ preferentially into the cytoplasmic peptide fraction and Cu 2+ into the cell-wall fraction, when grown under the subtoxic metal conditions. Under excess metal conditions, Cd-tolerant cells
produced greater amounts of Cd-binding peptides in the cytoplasm and retained lesser amounts of Cd 2+ ions in the cell wall than did wild-type cells. In contrast, tomato cells grown in the presence of Cu 2+ ions synthesized no detectable amounts of Cu-binding peptides in the cytoplasm and retained most of the Cu 2+ in the cell-wall fraction, irrespective of cell lines.
These results suggested that the cytoplasmic peptides rather than cell wall properties have a primary role in the response
of tomato cells to excess metal environments. 相似文献
3.
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
4.
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
5.
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
7.
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
8.
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
9.
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
10.
Addition of Cd 2+ or phenylarsine oxide (PhAsO) to respiring rat liver mitochondria results first in acidification of the medium (H + efflux) followed by disappearance of H + (discharge of the pH gradient or uncoupling). The first phase of H + efflux is dependent upon the presence of K + in the medium, and is not seen in the presence of valinomycin, which is consistent with the conclusion that H + efflux is linked to membrane potential-dependent uptake of K +. These effects are abolished by low levels of 2,3-dimercaptopropanol but potentiated by excess of 2-mercaptoethanol, showing involvement of a dithiol type of group in the response. Mersalyl produces only the H + efflux, and subsequent addition of Cd 2+ or PhAsO produces collapse of the pH.Abbreviations BAL
British Anti-Lewisite or 2,3-dimercaptopropanol
- 2-ME
2-mercaptoethanol
- PhAsO
phenylarsine oxide
- FCCP
carbonylcyanide trifluoromethoxyphenylhydrazone
- HEPES
N-2-hydroxyethylpiperazine- N-2-ethanesulfonic acid 相似文献
11.
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
12.
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
13.
One key step of the bioremediation processes designed to clean up heavy metal contaminated environments is growing resistant
cells that accumulate the heavy metals to ensure better removal through a combination of biosorption and continuous metabolic
uptake after physical adsorption. Saccharomyces cerevisiae cells can easily act as cation biosorbents, but isolation of mutants that are both hyperaccumulating and tolerant to heavy
metals proved extremely difficult. Instead, mutants that are hypersensitive to heavy metals due to increased and continuous
uptake from the environment were considered, aiming to use such mutants to reduce the heavy metal content of contaminated
waters. In this study, the heavy metal hypersensitive yeast strain pmr1∆ was investigated for the ability to remove Mn 2+, Cu 2+, Co 2+, or Cd 2+ from synthetic effluents. Due to increased metal accumulation, the mutant strain was more efficient than the wild-type in
removing Mn 2+, Cu 2+, or Co 2+ from synthetic effluents containing 1–2 mM cations, with a selectivity $ {\text{Mn}}^{{{\text{2}} + }} > {\text{Co}}^{{{\text{2}} + }} ~ > {\text{Cu}}^{{{\text{2}} + }} $ {\text{Mn}}^{{{\text{2}} + }} > {\text{Co}}^{{{\text{2}} + }} ~ > {\text{Cu}}^{{{\text{2}} + }} and also in removing Mn 2+ and Cd 2+ from synthetic effluents containing 20–50 μM cations, with a selectivity Mn 2+ > Cd 2+. 相似文献
14.
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
15.
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
16.
Light induced proton efflux in intact cells of Anabaena flos-aquae is inhibited by the heavy metals Hg 2+ and Cd 2+. Furthermore, Hg 2+ and Cd 2+ reduced the 14CO 2 fixation, oxygen evolution and carbonic anhydrase activity responsible for H + efflux. 相似文献
17.
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
18.
Tonoplast, ion antiport activities are critical to ion homeostasis and sequestration in plants. The biochemical properties of these activities, and the enzymes that catalyse them, are little characterized. Here we applied biochemical approaches to study some characteristics and to distinguish between Ca 2+/H + and Cd 2+/H + antiporter activities of tonoplast vesicles from non‐transformed, wild‐type plants. Solubilization and reconstitution of oat‐seedling ( Avena sativa L.) root tonoplast vesicles resulted in about a 6‐fold loss of protein, about a 6‐fold enhancement of Cd 2+/H + antiport specific activity (at 10 µ M Cd 2+), and almost complete loss of Ca 2+/H + antiport activity. Similar results were found for vesicles from mature tobacco ( Nicotiana tabacum) roots. Cd 2+ concentration‐dependent proton efflux was similar and linear with both oat vesicles and proteoliposomes. In contrast, Ca 2+ concentration‐dependent proton efflux of oat vesicles was easily observed while that with proteoliposomes was minimal and non‐linear. Cd 2+ pre‐treatment of oat vesicles reduced verapamil inhibition of Cd 2+/H + activity and verapamil binding to vesicles, while Ca 2+ pre‐treatment was much less protective of Ca 2+/H + activity and verapamil binding. Results show the usefulness of reconstitution, and also inhibitor/ion interaction assays for distinguishing between transporter activities in vitro, but they do not resolve the question of whether there are separate enzymes for Cd 2+/H + and Ca 2+/H +. Our observation that solubilization and reconstitution have similar effects on both Cd 2+/H + and Ca 2+/H + activities of root tonoplast vesicles from immature oat and mature tobacco roots suggests that the transporters involved are similar in young and mature roots, and in roots of different species. 相似文献
19.
The well-established killing of bacteria by copper surfaces, also called contact killing, is currently believed to be a combined effect of bacterial contact with the copper surface and the dissolution of copper, resulting in lethal bacterial damage. Iron can similarly be released in ionic form from iron surfaces and would thus be expected to also exhibit contact killing, although essentially no contact killing is observed by iron surfaces. However, we show here that the exposure of bacteria to iron surfaces in the presence of copper ions results in efficient contact killing. The process involves reduction of Cu 2+ to Cu + by iron; Cu + has been shown to be considerably more toxic to cells than Cu 2+. The specific Cu + chelator, bicinchoninic acid, suppresses contact killing by chelating the Cu + ions. These findings underline the importance of Cu + ions in the contact killing process and infer that iron-based alloys containing copper could provide novel antimicrobial materials. 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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