MT-like Proteins Research Articles

An in vitro study of the effect of reactive oxygen species on subcellular distribution of deposited cadmium in digestive gland of mussel Crenomytilus grayanus

The study was performed to assess in vitro effects of reactive oxygen species (ROS, oxyradicals) on intracellular distribution of accumulated cadmium in digestive gland of the mussel Crenomytilus grayanus. In vitro induction of ROS (by Fe/ascorbate reaction) in tissue homogenates of Cd-accumulated mussels led to a significant increase in lipid peroxidation (as conjugated dienes and malondialdehyde) and also to decrease in reduced glutathione and Cd-binding protein contents. Also fraction of MT-like proteins (20–22 kDa) has been shifted to a higher molecular weight area (40–45 kDa), which indicates dimerization of the protein. The level of intracellular vesicle-stored cadmium (within membrane compartments like lysosomes) was decreased significantly in oxyradicals-exposed tissue crude homogenate of mussels in comparison with controls. Additionally, Cd distribution among three weight classes of cytosol proteins has been significantly changed after ROS exposure. Taken together the results, there is a clear indication that ROS induce an oxidative stress resulting in damaging of intracellular Cd-binding compartments that may trigger (or contribute) the toxicity of this metal. Thus, from our experimental results and reviewed information follows that under high “pressure” of heavy metals on marine environment the aquatic organisms can show higher sensitivity to normal variations of natural factors of the environment or even decrease the range of tolerance to their variations.

Metallothionein induction and heavy metal accumulation in white shrimp Litopenaeus vannamei exposed to cadmium and zinc

Metallothioneins (MTs) have been widely considered for their potential use as specific biomarkers to reflect the existence of heavy metal pollution, because their induction has been observed to be obviously elevated after heavy metal exposure in a large number organism studied. However, relatively fewer efforts have been made in MT-related studies of prawn species, such as the white shrimp Litopenaeus vannamei, a globally important aquaculture species. With the results from gel filtration chromatography, we demonstrate the existence of MTs or MT-like proteins in L.vannamei. We further studied the relationship between MT induction and metals accumulation after long-term exposure to the heavy metals Cd and Zn. From our results, it is very clear that the response of L. vannamei to Cd differs from that to Zn, and this should be considered when using MTs in field applications to monitor metals contamination.

Metallothionein-like Proteins and Zinc–Copper Interaction in the Hindgut of Porcellio scaber (Crustacea: Isopoda) Exposed to Zinc

Metallothioneins (MTs) are ubiquitous low-molecular-weight metal-binding proteins, with a variety of functions in metal metabolism ascribed to them. Among terrestrial invertebrates, MTs have been studied in nematodes, insects, snails, and earthworms. The aim of this study was the characterization of MT-like proteins in the terrestrial isopod crustacean Porcellio scaber in order to analyze their probable role in the metabolism of copper (Cu) and zinc (Zn). Dietary Zn supplementation (793 microg Zn/g dry food, 6 d) was applied to stimulate MT synthesis. After separation of the hindgut post-microsomic supernatant (cytosol) of Zn-exposed animals by gel filtration on a Sephadex G-75 column, a Cu- and Zn-containing peak was detected in the position of Ve/Vo approximately 2, where MTs are expected to elute. Rechromatography of these fractions by size-exclusion chromatography-high-performance liquid chromatography revealed that the 215-nm absorbance peak coincided with the absorbance peak of the rabbit MT II standard. These low-molecular-weight Cu- and Zn-binding compounds, detected in the cytosol of the hindgut cells in Zn-exposed P. scaber, are considered to be Cu, Zn-MT-like proteins. To our knowledge, this is the first report on the characterization of MT-like proteins in isopod crustaceans. These results also indicate that both Zn and Cu dynamics in P. scaber hindgut are affected at the given dietary Zn supplementation and that MT-like proteins are involved in this Zn-Cu interaction.

Cloning and Expression of a Seed-Specific Metallothionein-Like Protein from Sesame

A cDNA clone, SiMT encoding an Ec type of metallothionein (MT)-like protein, was isolated from maturing seeds of sesame (Sesamum indicum L.), and its deduced protein sequence shared 47-65% similarity to other known Ec type of MT-like proteins with three highly conserved cysteine-rich segments. The transcript of SiMT was exclusively accumulated in maturing seeds from two weeks after flowering to the end of seed maturation. The results of a southern blot analysis suggested that one SiMT and one SiMT-like gene were present in the sesame genome. Recombinant SiMT fused with glutathione-S-transferase (GST) was over-expressed in Escherichia coli, and purified to homogeneity by affinity chromatography. Recombinant SiMT released from GST was harvested after factor Xa cleavage. Migration of the recombinant SiMT during SDS-PAGE was accelerated when its binding metal ions were depleted by EDTA. The metal-binding capability of recombinant SiMT was measured by inductively-coupled plasma atomic emission spectrometry. Our results show that the recombinant SiMT could trap zinc or copper ions, but not manganese ions, with a stoichiometric ratio (metal ion/SiMT) of approximately 2.

Cloning and characterization of type 2 metallothionein-like gene from a wetland plant, Typha latifolia

A type 2 metallothionein-like (MT-like) gene, tyMT, was cloned from Cattail ( Typha latifolia), a wetland plant with constitutional tolerance to heavy metals. The gene encoded a deduced peptide of 79 aa residues, containing the cysteine-rich domains, typical of plant type 2 MT-like proteins which included the presence of C-C, C-X-C, and C-X-X-C (X are other amino acids other than cysteine) motifs at amino-terminus and carboxy-terminus. Southern blot analysis suggested that the tyMT gene belongs to a multi-gene family. Northern blot hybridization results showed that the transcripts of the tyMT gene in root and shoot were differently regulated by heavy metals, such as Cu 2+ and Cd 2+, providing new information for plant MT-like genes. When expressing the tyMT in copper sensitive MT-deficient strain of yeast, it restored the yeast’s metal tolerance. Moreover, when the tyMT gene was introduced into Arabidopsis thaliana, the transgenic plants showed an increased tolerance to heavy metals, such as Cu 2+and Cd 2+. These results confirm that the tyMT gene is involved in heavy metal tolerance of T latifolia.

Endocrine disruption and health effects of caged mussels, Elliptio complanata, placed downstream from a primary-treated municipal effluent plume for 1 year

Freshwater mussels, Elliptio complanata, were caged in special benthic pens and were immersed at one upstream (Ups) site and two downstream sites (8 and 11 km) of a primary-treated municipal effluent plume for 1 year. The levels of metallothionein-like proteins (MT), lipid peroxidation, protein-free DNA strands and glutathione S-transferase (GST) activity were assayed in digestive gland, gill and gonad tissues to evaluate biological effects and damage. The levels of monoamines (serotonin and dopamine) in nerve ganglia, ATP-dependent transport activity and monoamine oxidase (MAO) activity were also investigated in the homogenates, synaptosomes and mitochondria, respectively. Results showed that significant amounts of sediment accumulated in cages and 82% of mussels survived the yearlong exposure period at the downstream sites. MT-like proteins were induced in all tissues with the following response intensity: gill (3-fold), digestive gland (1.4-fold) and gonad tissues (1.3-fold). Lipid peroxidation decreased (2.5-fold) in digestive gland but increased in gill (1.6-fold) and in gonad tissues (1.5-fold). GST activity was readily increased in digestive gland (2.5-fold), suggesting the presence of organic contaminants in the plume. Levels of protein-free DNA strands did not vary significantly in digestive gland and gill tissues but were significantly reduced in gonad tissues (2.5-fold) relative to the upstream site. In visceral nerve ganglia, both serotonin and ATP-dependent serotonin transport decreased 1.7-fold with a 4-fold increase of 5-hydroxyindole acetate (5-HIAA, a serotonin metabolite) level relative to the upstream site. However, MAO activity was somewhat reduced at downstream sites (0.7- to 0.9-fold of the activity at the upstream site). Dopamine levels were found to be decreased (1.5-fold), but dopamine ATP-dependent transport activity was increased 1.8-fold, suggesting reduced dopaminergic activity. These results indicate that estrogenic chemicals are likely at play, and the increased dopamine and decreased serotonin ATP-dependent transport suggest that the municipal plume was serotonergic for mussels located at the downstream sites. Mussels exposed for 1 year display a complex but characteristic pattern of responses that could lead to harmful health effects including neuroendocrine disruption of reproduction.

Metallothionein-like protein in the least killifish Heterandria formosa and its role in cadmium resistance.

Metallothioneins (MTs) are a class of low molecular weight, cysteine-rich, metal-binding proteins ubiquitous in animals. They function in metal regulation and detoxification. An MT-like protein was separated by gel-permeation high-performance liquid chromatography (HPLC) in the least killifish Heterandria formosa exposed to 6 mg/L of Cd for 26 h. Western blot analysis showed that this protein cross-reacted with a cod-MT antibody. We quantified MT-like protein levels by the Cd-hemoglobin saturation assay in fish from two Cd-resistant and two control laboratory populations. Fish from the resistant populations had higher MT-like protein levels than those from the control populations; this difference was found for basal levels and for levels after 26 h of exposure to Cd. Our results suggest that the MT-like protein detoxified Cd in the least killifish and accounted for at least part of the increased resistance in the Cd-resistant laboratory populations.

Quantification of metallothionein in whole body gammarus locusta (crustacea: amphipoda) using differential pulse polarography

A polarographic method was optimised for the quantitative determination of metallothionein (MT) in whole body Gammarus locusta (Crustacea: Amphipoda). The identity of the MT-like proteins was examined using electrophoretic analysis (SDS-PAGE) and induction studies (water-borne exposures to copper). The MT-method was then used to examine changes in MT levels over the lifetime (juveniles, sub-adults and adults) of a laboratory population of G. locusta; copper (Cu) and zinc (Zn) body burden were also measured by flame atomic absorption spectrometry. MT was quantified by heat-denaturation of 30 000 g supernatants (to remove the bulk of non-MT proteins) followed by differential pulse polarography (DPP) to measure sulphydryl-group containing proteins. DPP proved to be a sensitive and reliable method to quantify heat-stable total sulphydryl-proteins. The majority of the latter was indicated to be MT from SDS-PAGE and induction studies. SDS-PAGE revealed a putative MT of 23 ± 0.6 kDa app. mol. wt., consistent with the average size of dimeric MTs (10–20 kDa) found in several aquatic invertebrate species. Copper-exposure revealed parallel increases in the amounts of 23 kDa protein and total sulphydryl-proteins. Levels of whole body MT (rabbit pure MT as standard) range between 1.3 and 2.3 mg g−1 dry wt. over the lifetime of G. locusta. Sex-related changes in MT status were observed, the levels in females being 1.6 times higher than in males (p<0.05). Copper and Zn body content changed over the lifetime of G. locusta, the levels in juveniles (p>0.05) and sub-adults (p<0.05) being higher than in adults. It is concluded that the inclusion of MT in ecotoxicological studies with amphipod crustaceans require some caution with respect to the stages of moulting and/or sexual maturation of organisms, but this should not provide any major impediment in its use in metal pollution monitoring.

Molecular cloning of two metallothionein-like protein genes with differential expression patterns from sweet potato ( Ipomoea batatas) leaves

Metallothionein (MT) is a group of proteins with low molecular masses and high cysteine contents, and is classified into different types, which in general contains two domains (domain 1 and domain 2) with typical amino acid sequences (Rauser 1999). In this report two full-length cDNAs (Y459 and G14) encoding MT-like proteins were isolated from leaves of sweet potato (Ipomoea batatas). Their open reading frames contained 249 and 195 nucleotides (82 and 64 amino acids) for Y459 and G14, respectively, and exhibited a relatively low amino acid sequence similarity (ca. 25.8%). Gene structure studies showed that Y459 had the conserved domain 1 region of type 2 MT; however, the domain 2 region was not conserved and contained additional amino acids between the CxC and CxC spacing. G14 had conserved domains 1 and 2 of type 4 MT except that the last CxC of domain 2 was changed to RxC. Semi-quantitative RT-PCR showed that Y459 was expressed in significant quantity in roots and stems, but was much less in green leaves. During natural and induced (with dark and ethephon, an ethylene-releasing compound, treatments) leaf senescence, Y459 gene expression was significantly enhanced. In contrast, relatively constant gene expression levels were found for G14 in all tissues or treatments analyzed. In conclusion, the two MT-like protein genes of sweet potato display differential gene structures and gene expression patterns, which may be associated with the diverse roles and functions they play in plant physiology in order to cope with particular developmental and environmental cues.

Indirect Measurement of Biologically Important Compounds by Means of X-Ray Microanalysis

The main objective of our work was to investigate the possibility and usefulness of indirect methods in X-ray microanalysis for the quantification of biologically important compounds. Metallothionein-like proteins (MT-like proteins) from kidney and liver, rich in sulfur were chosen as an indicator of heavy metal presence in cells and their environment. Tissues from goldfish (Carassius auratus gibelio) were sampled after short and prolonged periods of exposure to Co+2, CrO4−2, Pb+2, Cu+2 and control treatment and prepared for histochemical staining for peroxidated thiolate groups. Commonly used –S–S– bonds dye (Nitro Red) was replaced with iodine atoms and they were quantified at L line by means of X-ray microanalysis combined with SEM. After fish treatments with heavy metal solutions changes in MT-like proteins and in I atom contents were expected. There was statistically significant decrease in MT-like proteins level in kidney after lead treatment (Pb/C = 0.62). In liver a statistically significant increase in MT-like proteins concentration was observed after chromium, cobalt and lead ions treatment in comparison to control animals. The following ratios were noted: 3.04 for Cr/C, 2.18 for Co/C and 2.10 for Pb/C. Our finding indicates that the method of indirect measurement of MT-like proteins in fish and other animal tissues is possible. The concentration of iodine atoms is above their detection level by EDS and their changes are possible to identify. During histochemical procedures it is worth taking into account sample preparation methods which might disturb the quality and quantity of the analysed material.

Mushrooms from two metal-contaminated areas in Norway: occurrence of metals and metallothionein-like proteins

This study tested the hypothesis that concentrations of metallothionein-like (MT-like) proteins in fruiting bodies of wild-growing macrofungi reflect exposure to the metals Cd, Cu and Zn. Screening for these proteins was done by taking 44 samples of seven species of macrofungi from two metal-polluted areas in Norway, namely Odda and Sulitjelma. Concentrations of Cd, Cu and Zn were measured in fruiting bodies and topsoil, the highest of which were observed in fruiting bodies – 126 μg g −1 for Cd, 427 μg g −1 for Cu and 396 μg g −1 for Zn. A large intra- and inter-specific heterogeneity in metal uptake was displayed between fruiting bodies from the same soils. Cd,Zn–MT-like proteins were detected in all samples, except one stipe of Boletus edulis , whereas only 72% of the samples contained detectable levels of Cu–MT-like proteins. However, concentrations of MT-like proteins did not reflect variations in metal concentrations. Low content of cysteine in Cd-binding protein fractions from Amanita muscaria collected in Odda indicates that no proteins of the metallothionein family were present in this species. Onthe contrary, these protein fractions share several characteristics with cadmium–mycophosphatins.

Concentrations of Cadmium, Zinc, Copper, Iron, and Metallothionein in Liver and Kidney of Nonhuman Primates

To evaluate the species specificity of Cd accumulation and the relationship of Cd with other essential metals and metallothionein (MT), the concentrations of Cd, Zn, Cu, and Fe in the liver and kidney and the MT concentrations in the soluble fractions of the liver and kidney were determined in Cd-uncontaminated nonhuman primates (11 species, 26 individuals) kept in a zoo and two wild-caught Japanese macaques. The compositions of metal-binding proteins in the soluble fractions were also investigated by high-performance liquid chromatography (HPLC). The hepatic Cd concentration was 0.03-14.0 microg/g and the renal Cd concentration was 0.35-99.0 microg/g, both varying greatly and being higher in nonhuman primates, which were more closely related to man. The hepatic Zn concentration was 24.0-176 microg/g and the renal Zn concentration was 13.5-138 microg/g, showing 7- to 10-fold differences, and a correlation (r=0.558, p<0.01) was found between renal Zn and renal Cd concentrations. It was proved that in the liver, MT is more closely correlated with Zn (r=0.795, p<0.001) than with Cd (r=0.492, p<0.01) and that in the kidney MT is correlated with both Cd (r=0.784, p<0.001) and Zn (r=0.742, p<0.001). HPLC analysis of metals bound to MT-like protein in chimpanzees, de Brazza's monkeys, and Bolivian squirrel monkeys showed that more than 90% of Cd in both the liver and kidney, approx 40% of Zn in liver and 28-69% of Zn in kidney were bound to MT-like protein. The higher percentage Zn was bound to high-molecular protein.

Metallothionein induction and condition index of dogwhelks Nucella lapillus (L.) exposed to cadmium and hydrogen peroxide

It has been suggested that metallothionein (MT) not only can regulate essential metals and detoxify toxic metals, but that MT can also play a significant role as an antioxidant and can be induced by oxidative stresses other than metals. This study is aimed at investigating the effect of hydrogen peroxide (H 2O 2), and the combined effect of H 2O 2 and cadmium (Cd) on MT induction and condition index (CI) in dogwhelks Nucella lapillus. Adult male dogwhelks (27±1 mm in shell length) were exposed for 20 days to (1) control (filtered natural seawater only); (2), 0.50 ppm Cd; (3) 2.0 ppm H 2O 2 + 0.50 ppm Cd; (4) 1.0 ppm H 2O 2 + 0.25 ppm Cd; (5) 2.0 ppm H 2O 2; (6) 1000 ppm H 2O 2 or (7) 1000 ppm H 2O 2 + 0.50 ppm Cd. The concentration of MT in the Leiblein gland of N. lapillus was quantified using the silver saturation method. MT or MT-like proteins in the animals were induced by Cd (0.5 ppm), H 2O 2 (2.0 ppm) or Cd + H 2O 2, indicating that MT in this gastropod species can be induced by either metal or oxidative stresses. Exposure to high H 2O 2 (1000 ppm) alone or combined with Cd, and exposure to Cd (0.50 ppm) or H 2O 2 (2.0 ppm), resulted in significant weight loss, indicated by a reduction of CI. However, CIs of groups (3) and (4) were similar to that of the control suggesting that Cd antagonistically reduces toxicity caused by H 2O 2 since Cd-induced MT may have a protective function against hydroxyl radicals.

Relationship between metallothionein and metal contents in red-blooded and white-blooded Antarctic teleosts

Metal bioaccumulation and metallothionein were investigated in different organs of the red-blooded teleost, Trematomus bernacchii and the haemoglobinless Chionodraco hamatus. Specimens of the two Antarctic fish were sampled from Terra Nova Bay (Ross Sea), and their levels of Cd, Cu and Zn in homogenates and in soluble fractions of liver, muscle, gills, heart and plasma were determined. Dosages of metallothioneins (MTs) or MT-like proteins were assayed by the silver saturation method in soluble fractions of the same organs. In both T. bernacchii and C. hamatus the highest MT contents were found in liver. Hepatic MT and Cd, Cu and Zn concentrations correlated positively in T. bernacchii, whereas in C. hamatus hepatic MT showed a positive correlation only with Cd. Positive correlations were also found between Cd and MT in gills of the two species. A metal-binding protein containing a high percentage of cysteine from C. hamatus was purified and compared with the MT from T. bernacchii and mammals.

Purification, cDNA cloning and expression of a cadmium-inducible cysteine-rich metallothionein-like protein from the marine sponge Suberites domuncula

During the last few years sponges have been proven to be suitable model organisms for biomonitoring programmes. Previously it was reported that the marine sponge Suberites domuncula reacts to cadmium, both under controlled laboratory conditions and in the field with an increased expression of the heat-shock protein 70 and with DNA damage. In this study it is shown that this sponge contains a cadmium-binding protein with a M, of 24 000. Cloning studies detected a gene in S. domuncula, termed SDMTL, which encodes a putative polypeptide, MTL-SUBDO, that shares high sequence similarity with metallothioneins (MTs) from Metazoa. The open reading frame dis- plays a polypeptide with a calculated size of M, of 17 103. Phylogenetic analysis revealed that the sponge molecule, termed MT-like (MTL) protein, is related to the metazoan MTs. Under laboratory conditions, no expression of the SDMTL can be detected. After 1 d, incubation of the sponges with cadmium (200 pg 1-l) already revealed a dramatic upregulation of the MTL gene in S. domuncula. Subsequent studies in the field, the area around Rovinj (Croatia), demonstrated a correlation between the environmental load with cadmium (accumulation of this metal in the animals) and the expression of the gene encoding the 'detoxifying' cadmium-binding protein, MTL, in the test ani- mals. These data suggest that the discovered MTL gene from S. domuncula is a sensitive indicator for environmental, bioavailable cadmium.

Effect of arsenic trioxide on metallothionein and its conversion to different arsenic metabolites in hen liver.

The metabolism of arsenic, its affinity to metallothionein (MT), its influence on selenium levels, and its biotransformation to different metabolites in the liver tissue of laying hens exposed to arsenic trioxide (As2O3) was investigated. The experiment was performed with two groups of hens fed for 19 d with either a standard diet or with the same diet enriched in arsenic (30 microg/g). The major findings were as follows: 1. After 19 d exposure, about 65% of the total liver As was found in the water-soluble phase (100,000g centrifuged supernatant). In liver supernatant, As binding was found mostly in the range of very low-molecular-weight proteins (Mr < 10,000). Although after exposure the amount of MT-like proteins increased, the As bound to it was only in trace amounts. The protein was identified by convential procedures as Zn,Cu-thionein with traces of selenium and arsenic. 2. Arsenic exposure resulted in almost unchanged Se levels regarding its tissue concentrations and distribution between supernatant and pellet, where about 10% of total Se was found in the supernatant. On the contrary, As exposure did affect Cd levels. Tissue Cd concentration was slightly diminished, but the percentage of tissue Cd found in the water-soluble phase was increased from 20% to 40%. 3. In methanol extracts of tissue and supernatant of the As-exposed group, only two arsenic compounds were detected, As(III) and dimethylarsinic acid (DMA), the latter prevailing.

Seasonal variations in hepatic and ovarian zinc concentrations during the annual reproductive cycle in female channel catfish ( Ictalurus punctatus)

Seasonal variations in hepatic and ovarian zinc concentrations were studied during the reproductive cycle in female channel catfish ( Ictalurus punctatus). The gonadal somatic index (GSI) increased dramatically in April and peaked in June prior to spawning. Exogenous vitellogenesis was initiated in the fall as noted by increases in serum estradiol and testosterone and liver somatic index (LSI). Total hepatic zinc and zinc in the cytosolic high-molecular weight (HMW) and metallothionein-like (MT) fractions were elevated in March but decreased during rapid vitellogenic oocyte growth in April and May. Following spawning in July, total hepatic zinc and zinc in the HMW and MT-like fractions were again elevated. Total ovarian zinc and zinc associated with HMW and MT-like fractions increased with GSI, then decreased to a low after spawning. However, on a per g tissue basis, ovarian zinc concentrations in both cytosolic pools declined during rapid oocyte growth, indicating a different intracellular localization of the zinc binding proteins. Hepatic MT-like proteins exhibit UV absorption profiles similar to mammalian MT while the ovarian proteins appear to be different. Results give evidence for the homeostatic regulation of hepatic zinc by MT during exogenous vitellogenesis and a similar function for the ovarian MT-like protein during oocyte development.

Isolation of Metallothionein-Like eDNA Clone from Buckwheat

Summary We have isolated eDNA clone pBM 290 from the eDNA library of developing buckwheat seed, encoding a 59-amino-acid-long metallothionein-like (MT-like) protein. Two domains with abundant cysteine residues, characteristic for the type of MT, showed the highest homology with the MT 3 protein from Arabidopsis and with deduced amino acid sequences of a few eDNA clones for MT-like proteins from ripening fruits. The expression of buckwheat MT mRNA was not specific for seeds.

Heavy Metal-Binding Peptides and Proteins in Plants. A Review

In plants, two kinds of specific metal-binding peptides or proteins are synthesized. Plant metallothioneins (MTs) and MT-like proteins are cysteine-rich translation products of genes inducible in tissue-specific manner during embryogenesis and plant development. In addition, differential expression of MT-like protein genes could be due to variation of external heavy metal concentrations (especially of Cu2+ and Fe2+), influence of various stress factors (heat shock, sucrose starvation, oxidative stress, wounding, plant pathogens). The principal role of plant MTs and MT-like proteins seems to be in homeostasis of essential transition metals rather than in metal detoxification. Phytochelatins (PCs) have general structure (γ-Glu-Cys)n-Xaa, where n = 2-11 and Xaa amino acids Gly, β-Ala, Ser, and Glu which depend on the species; the des-Xaa forms of PC also exist. PCs are synthesized in plants and some yeasts by a constitutive enzyme phytochelatin synthase (active only in the presence of free heavy metal ion) from glutathione or its anologue. Despite the PC capability of forming complexes with transition metal ions (their role in metal homeostasis could not be excluded) and virtually prominent role in Cd2+ detoxification within plant cell, there is no evidence that elevated production of PCs may contribute to differential tolerance and/or could be responsible for the resistance to toxic metals. A review with 172 references.

Effect of zinc and cadmium treatment on hydrogen peroxide-induced mortality and expression of glutathione and metallothionein in a teleost hepatoma cell line

Cellular thiols such as glutathione (GSH) and metallothioneins (MTs) have been shown to protect cells from metal toxicity by nature of their ability to sequester metals. Thiols are also scavengers of reactive oxygen species and protect against oxidative stress. Few studies have examined the role of thiols in protection from oxidative stress in aquatic species. To examine the role of MT and GSH in oxidative stress in fish, Poeciliopsis hepatoma cells (PLHC-1) were treated with 0.1, 1.0 and 10 mM of the oxidant, hydrogen peroxide (H 2O 2), for 24 h. When cells were pretreated with 10 μM ZnSO 4 for 24 h prior to H 2O 2 treatment, survival was not significantly different than controls at the 0.1 mM H 2O 2 concentration. However, 10 μM ZnSO 4 provided no protection at the 1.0 and 10 mM H 2O 2 concentrations. When cells were pretreated with 10 μM CdCl 2 24 h prior to H 2O 2, significant protection was afforded at the 0.1 and 1.0 mM H 2O 2 concentrations. Low-molecular weight 109Cd-binding proteins (indicative of (MTs)) were measured in each group of cells 24 h after 0.1, 1.0 and 10 μM ZnSO 4 or CdCl 2 treatments and was significantly induced by CdCl 2 at the 1 and 10 μM concentrations. Significant induction of MT-like proteins were only observed at the 10 μM ZnSO 4 concentration and H 2O 2 failed to induce MT-like proteins in the cells. Cellular GSH was also measured following metal and H 2O 2 treatments. Treatment of cells with 10 μM CdCl 2 led to significant increases in GSH, whereas ZnSO 4 failed to change GSH content. H 2O 2 treatments of 1 and 10 mM led to a reduction of GSH. These data indicate differential protection afforded by the two metals and suggests that metal-induced GSH and MT may provide better protection against oxidative damage than induction of MT alone.