On metallothionein,cadmium, copper and zinc relationships in the liver and kidney of adult rats

1. A short-term exposure of adult Wistar rats to Cu (50 μg/ml) and Cd (10.0 μg/ml drinking water) caused significant changes in the subcellular concentrations of Cd, Cu, Zn and metallothionein (MT) in the liver and kidney; the concentrations were close to the physiological values, however.2. To establish a relationship between these changes in the subcellular concentrations of Cd, Cu, Zn and the level of MT in the post-mitochondrial fraction of the liver and kidney, the analytical data (N = 42) were subjected to the multiple regression analysis.3. The analysis showed that MT synthesis in the liver was principally induced by small amounts of Cd (0.32–1.4 μg/g wet wt) whereas in the kidney a level of MT in the post-mitochondrial fraction correlated positively with the renal Cd and Cu, as well as with the level of this protein in the liver.4. The above results together with the positive correlation between the level of MT in the post-mitochondrial fraction and the concentration of Cu in this fraction, as well as the fact that under normal physiological conditions the capacity of MT (β-domain) in the liver and kidney was sufficient to bind 50–100% of the total post-mitochondrial Cu suggest that MT, first induced by small amounts of Cd, may be involved in the metabolism of Cu.     

Metal concentrations in the liver and kidney of aquatic mammals and penguins

We determined the hepatic and renal concentrations of Cd, Pb, Zn, Cu, and Fe in (1) marine mammals (three bottle-nosed dolphins, six California sea lions, and one sea otter), (2) freshwater and brackish-water mammals (one Oriental short-clawed otter and four European river otters), and (3) sea birds (three rock-hopper penguins, two king penguins, three Humboldt penguins, four Macaroni penguins, and four Magellanic penguins), all of which were kept in a zoo and an aquarium in Japan. We investigated the species-specificity of Cd accumulation in these aquatic animals. We also presented the basic data on metal concentrations. The concentrations of Cd in liver and kidney tended to be higher in marine mammals than in freshwater mammals. Many penguins, sea birds, showed high Cd concentrations. These results suggest that the habits of these animal species may be involved in accumulation of Cd. Pb concentrations were below the detection limit or low in both liver and kidney [not detected (ND)=0.132 μg/g and ND=0.183 μg/g, respectively]. The hepatic concentrations of Zn and Cu were high in young animals. In penguins, a positive correlation was found between the Zn and Cd concentrations in the liver and kidney and between the Cu and Cd concentrations in the liver. Individual variation was large in Fe concentration (48–3746 μg/g in the liver and 51–980 μg/g in the kidney).     

Age-dependent changes in metallothionein levels in liver and kidney of the Japanese

Samples of liver, renal cortex, and medulla were obtained from 55 forensic autopsies (0- to 95-yr-old Japanese). Metallothionein (MT) was determined by the Ag-hem or Cd-hem method. Zinc (Zn), copper (Cu), and cadmium (Cd) were determined by atomic absorption spectrophotometry. The mean levels of MT were 250 μg/g in the liver, and 394 μg/g (cortex) and 191 μg/g (medulla) in the kidney. Age-dependent changes were observed in both the liver and kidney. In the liver, MT level decreased during infancy and increased thereafter with age. Similar age-dependent changes in the levels of Zn and Cu were observed. In the kidney cortex, MT level increased with age, although no correlation was found after middle age. The levels of Cd and Zn also increased with age until middle age; however, they decreased thereafter. These results suggest that age-dependent changes in renal MT levels are associated with accumulation of Cd.     

Metal composition of human hepatic and renal metallothionein

This article is based on data on the levels of metals (Cd, Zn, Cu) and metallothionein (MT) determined radiochemically with²⁰³Hg in renal cortex and liver of 137 autopsy cases. From this number, for 23 cases, the gel filtration of the cytoplasmic fraction of the organs was performed. The molar content of metals in the MT fraction (Sephadex G-50) amounted to 46.9, 50.2, and 2.0% for Cd, Zn, and Cu in renal cortex, respectively, and to 8.3, 83.6, and 9.1% for Cd, Zn, and Cu in the liver, respectively. In parallel with the increase of Cd and MT in renal cortex, increasing saturation was found of the MT fraction by Cd, occurring at the expense of Zn and Cu. Equimolar amounts of Cd and Zn in the MT fraction are found at Cd level of 0.5 μmol Cd/g wet wt of renal cortex. In the liver, analogous dependency (elevation of %Zn, depression of %Cd and %Cu) were observed in relation to Zn and MT levels in this organ. The basic level of Zn (not bound with MT) was estimated at 0.5 μmol/g for both renal cortex and liver. A deficit of non-MT Zn in kidneys is proposed as an alternative mechanism of toxic Cd action.     

Metal accumulation and metallothionein in brown trout, Salmo trutta, from two Norwegian rivers differently contaminated with Cd, Cu and Zn

In this work we have studied the accumulation of heavy metals in two brown trout (Salmo trutta) populations in their natural environment and the participation of metal binding to metallothionein (MT) in this process. Cd, Cu and Zn concentrations, total MT (including Cu MT) and Cd/Zn MT were measured in the gills, liver and kidney of trout inhabiting two rivers, one Cu-contaminated and the other Cd/Zn-contaminated, located at Røros, Central Norway. In both populations, high levels of Cu were found in the liver, whereas Cd was accumulated in liver and particularly in the kidney. The proportions of Cd/Zn MT and Cu MT in liver and kidney, but not in gills, reflected the accumulated and the environmental concentrations of these metals. The total Cu MT concentrations in the investigated tissues, however, were highest in trout from the river with the lowest ambient Cu concentration. It is suggested that MTs are of less importance in Cu-acclimated trout. The data also suggest that acclimation to a Cu-rich environment involves reduced Cu accumulation or increased Cu elimination. In trout from the Cd-rich environment, this metal was mainly bound to MT, whereas in trout from the Cu-rich environment Cd was also associated with non-MT proteins. These findings emphasize the importance to determine both Cd/Zn MT and Cu MT levels, when the participation of this protein in metal handling in trout tissues is investigated.     

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.     

Effects of Chronic Cadmium Poisoning on Zn, Cu, Fe, Ca, and Metallothionein in Liver and Kidney of Rats

An experiment was conducted to invest effects of chronic cadmium poisoning on Zn, Cu, Fe, Ca, and metallothionein gene expression and protein synthesis in liver and kidney in rats. Forty rats, 6?weeks old, were randomly allocated into two groups. A group was given CdCl(2) (1?mg/KgCd(2+)) by intraperitoneal injection once a day. The other group was treated with normal saline in the same way. Liver and kidney were collected for analysis at the end of the third week. Results showed that Cd exposure increased Cd (P?相似文献   

Combined Effect of Dietary Cadmium and Benzo(a)pyrene on Metallothionein Induction and Apoptosis in the Liver and Kidneys of Bank Voles

Bank voles free living in a contaminated environment have been shown to be more sensitive to cadmium (Cd) toxicity than the rodents exposed to Cd under laboratory conditions. The objective of this study was to find out whether benzo(a)pyrene (BaP), a common environmental co-contaminant, increases Cd toxicity through inhibition of metallothionein (MT) synthesis-a low molecular weight protein that is considered to be primary intracellular component of the protective mechanism. For 6 weeks, the female bank voles were provided with diet containing Cd [less than 0.1 μg/g (control) and 60 μg/g dry wt.] and BaP (0, 5, and 10 μg/g dry wt.) alone or in combination. At the end of exposure period, apoptosis and analyses of MT, Cd, and zinc (Zn) in the liver and kidneys were carried out. Dietary BaP 5 μg/g did not affect but BaP 10 μg/g potentiated rather than inhibited induction of hepatic and renal MT by Cd, and diminished Cd-induced apoptosis in both organs. The hepatic and renal Zn followed a pattern similar to that of MT, attaining the highest level in the Cd + BaP 10-μg/g group. These data indicate that dietary BaP attenuates rather than exacerbates Cd toxicity in bank voles, probably by potentiating MT synthesis and increasing Zn concentration in the liver and kidneys.     

Metal constitution of metallothionein influences inhibition of delta-aminolaevulinic acid dehydratase (porphobilinogen synthase) by lead.

This study was undertaken to evaluate the effect of Zn and Cd pretreatment on the inhibition of delta-aminolaevulinic acid dehydratase (ALAD; porphobilinogen synthase, EC 4.2.1.24) by Pb. Male CD rats were pretreated with 200 mumol of Zn/kg s.c. (subcutaneously) or 18 mumol of Cd/kg s.c., 48 and 24 h before assay of ALAD. Pretreatment with Zn resulted in activation of hepatic and renal ALAD and attenuated the inhibition of this enzyme by Pb in vitro. Pretreatment with Cd increased hepatic ALAD activity, and the inhibitory effect of Pb on the hepatic enzyme was attenuated in this group. In contrast with the situation in liver, pretreatment with Cd did not affect the activity of renal ALAD and did not alter the inhibitory effect of Pb on the renal enzyme. The Pb IC50 (concentration causing half-maximal inhibition) values for hepatic and renal ALAD in Zn-pretreated rats and for hepatic ALAD in Cd-pretreated rats were increased above control, whereas the IC50 for renal ALAD in Cd-pretreated rats was unchanged. Cytosolic binding patterns for the three metals were assessed by gel-filtration chromatography and disclosed that 203Pb was co-eluted with Zn and Cd bound to liver and kidney Zn-thioneins and liver Cd,Zn-thionein, although minimal binding of 203Pb to kidney Cd,Zn-thionein was observed. Estimation of the molar ratio of metals bound revealed Cd/Zn ratios of 2 and 5 for Cd,Zn-thioneins from liver and kidney respectively. The inhibition of purified ALAD by Pb was also attenuated by addition of purified Zn-thioneins and Cd,Zn-thioneins from liver and kidney in the following order: liver Zn-thionein = kidney Zn-thionein greater than liver Cd,Zn-thionein much greater than kidney Cd,Zn-thionein. Thus liver and kidney Zn-thioneins and liver Cd,Zn-thionein with a low Cd/Zn ratio readily decrease the free pool of Pb available to interact with ALAD. These data also demonstrate that the capacity of metallothionein to alter the intracellular distribution of Pb and mediate the inhibition of ALAD by Pb is dependent on the tissue source and relative metal constitution of the metallothionein.     

Cadmium-bound metallothionein induces apoptosis in rat kidneys, but not in cultured kidney LLC-PK1 cells

The ability of cadmium-bound metallothionein(Cd-MT) to induce apoptosis was investigated in vivo and in vitro. Administration of purified Cd-MT (0.15 mg MT bound Cd per kg body weight) to the rat induces DNA fragmentation, a biochemical characteristic of apoptosis in the kidney at 16 h, which was detectable by ethidium bromide staining on an agarose gel. It was still detected 24 h after administration. Induction of apoptosis by Cd-MT was specific to kidney; it was not observed in cerebrum, cerebellum, heart, lung, liver, testis, dorsolateral prostate, and ventral prostate. In contrast, addition of Cd-MT (0.01-100 microM) to the cultured porcine kidney LLC-PK1 cells failed to induce apoptosis under the condition where cadmium chloride (10 microM) did. There was no additivity of induction of apoptosis by CdCl2 (10 microM) in the presence of Cd-MT (0.01-100 microM). To examine the effect of intracellular MT on cadmium-induced apoptosis in cultured cells, new cell lines were established, which constitutively produce MT, being termed as Cd(r)-LLC-PK1 cells since Cd-MT exogenously added had much less permeability to the cultured cells. Followed by exposure of wild-type LLC-PK1 cells to 50 microM CdCl2 for 24 h, the surviving cells(Cd(r)-LLC-PK1 cells) induce MT at the level of 1.9 microg/2 x 10(6) cells. In Cd(r)-LLC-PK1 cells, 10 microM CdCl2 failed to induce apoptosis, but 60 microM CdCl2 could exert the apoptotic response, indicating that intracellular MT which was induced by CdCl2 did not facilitate CdCl2-elicited apoptosis. Furthermore, chromatin in rat kidneys was condensed by Cd-MT, but not that in LLC-PK1 cells. Thus, Cd-MT induces apoptosis in rat kidneys, but not in the cultured renal cells, suggesting that the ionic form of cadmium was required for programmed cell death.     

Age- and tissue-dependent metallothionein and cytosolic metal distribution in a native Mediterranean fish, Mullus barbatus, from the Eastern Adriatic Sea

The levels of metallothionein (MT), a biomarker of metal exposure, and of cytosolic metals (Zn, Cu, Cd), known as MT inducers, were investigated as variables of age (1 to 8 years) and tissue mass (liver, kidney, brain) of red mullet (Mullus barbatus). Within the age from 1 to 8 years the most significant increase is evident for cytosolic Cd in liver (43-fold) and in kidney (5-fold). MT and essential metals are constant with age or slightly increased. Over the growth period, statistically significant MT and metal increase is evident only between 1 and 6-8 years old specimens, while for Cd in liver and kidney cytosol significant increase already exists at 4 years old specimens. Metal distribution in all tissues follows the order: Zn>Cu>Cd, with even 500-800 times lower Cd levels than essential metal levels. Consequently, MTs follow the levels of essential metals, Zn and Cu, indicating MT involvement in homeostasis of essential metals. In contrast to kidney and brain, hepatic MT levels are not age-dependent. Inclusion of hepatic MT measurements and the associated cytosolic metals will be useful in the assessment of long-term metal effects in demersal fish M. barbatus.     

Binding properties and stoichiometries of a palladium(II) complex to metallothioneins in vivo and in vitro

This paper will be the first to discuss the in vivo and in vitro properties of a Pd(II) complex, K2PdCl4, interacting with metallothioneins (MTs). In vivo experiments revealed that intraperitoneal injections of K2PdCl4 into rabbits led to the simultaneous synthesis of Pd-MT in the kidney and Zn7MT in the liver. The renal Pd-MT complex contains 3.6 +/- 0.3 Pd, 2.1 +/- 0.2 Zn, and 1.0 +/- 0.1 Cu per mole protein. It was found that pre-treatment with Zn(NO3)2 before K2PdCl4 injections significantly enhanced renal Pd-MT level. The same pre-treatment also increases hepatic Zn-MT levels. These results strongly suggest that Pd(II) ions can be bound in vivo by MT existing in the rabbit kidneys to form Pd-MT. Gel-filtration chromatographic studies after the incubation of either native Cd5Zn2MT2 or Zn7MT2 with K2PdCl4 in vitro demonstrate that Pd(II) ions promote the non-oxidative oligomerization of native MTs. Increasing the level of Pd(II) relative to MT led to a concomitant increase in the apparent yield of MT oligomers. At relatively low Pd-MT ratio, Pd(II) is found predominantly in the oligomers while the monomeric products are chiefly composed of the reactants, Cd5Zn2MT2 or Zn7MT2. Based on our experimental data, the mechanisms of the reactions between Pd(II) and MTs in vivo and in vitro are discussed.     

Alterations of tissue glutathione levels and metallothionein mRNA in rainbow trout during single and combined exposure to cadmium and zinc

The objective of this study was to assess the effects of Cd and Zn exposure of rainbow trout (Oncorhynchus mykiss) on (a) hepatic glutathione (GSH) levels; and (b) hepatic and branchial metallothionein (MT) mRNA expression. Juvenile rainbow trout were exposed to waterborne Cd (nominal concentrations: 1.5 or 10 microg Cd l(-1)), Zn (150 or 1000 microg Zn l(-1)) or Cd/Zn mixtures (1.5 microg Cd l(-1) with 200 microg Zn l(-1) or 10 microg Cd l(-1) with 1000 microg Zn l(-1)). After 14 and 28 days of treatment, hepatic concentrations of total glutathione, oxidized glutathione (GSSG) and cysteine were determined by means of fluorometric high performance liquid chromatography (HPLC). Branchial and hepatic expression of MT mRNA was measured by means of semi-quantitative RT-PCR. Exposure of trout to Zn did not result in significantly elevated tissue levels of Zn, whereas Cd accumulation factors changed significantly with time and concentration. Despite of the absence of Zn accumulation, hepatic GSH but not MT mRNA levels were significantly altered in Zn-exposed fish. Cd, on the contrary, affected mainly the MT response but not GSH. Also tissue specific differences in the regulation of the two thiol pools were expressed. The thiol response after exposure to metal mixtures could not be explained by simple addition of the effects of the individual metals. The results indicate that cellular thiol pools show different reaction patterns with respect to specific metals and metal mixtures. Under conditions of long-term, low dose metal exposure, the function of GSH appears to go beyond that of a transitory, first line defense.     

Cadmium-induced oxidative stress and DNA damage in kidney of pregnant female rats

In the present study, we have investigated the influence of sub-acute treatment with cadmium (Cd) on some parameters indicative of oxidative stress and DNA damage in tissues of pregnant female rats. Pregnant female rats (n=6) were injected subcutaneously, daily with a dose of cadmium chloride of 3 mg/kg body weight (b.w.) from day 6 to day 19 of pregnancy, and they were allowed to deliver normally. MDA level and GPx, CAT and SOD activities were used as markers of oxidative stress in liver and kidney. The 8-oxo-dG level was measured by the HPLC-EC system. Cd treatment increased MDA (+116%, p<0.01) in kidney. Moreover, Cd treatment also decreased CuZn-SOD (-11%, p<0.05) and GSH level (-52%, p<0.05) in kidney. Treated rats displayed an increase of the liver metallothionein (MT) level. Induction of MT in liver was probably implicated in the detoxification of Cd. The high level of Cd (3 mg/kg) used in the present study is partially neutralized by MT in liver, whereas the free fraction could be implicated in the oxidative stress and DNA oxidation observed in kidney. Cd treatment failed to alter 8-oxodGuo, indicating the absence of DNA oxidation in liver; by contrast, the same treatment increased the 8-oxodGuo level (+51%, p<0.05) in the kidney of pregnant female rats, indicating an oxidative stress associated with DNA damage only in kidney.     

Properties of metallothionein induced by zinc, copper and cadmium in the frog, Xenopus laevis

1. Repeated injections of zinc (Zn) and copper (Cu) into the frog Xenopus laevis caused accumulations of the respective metals in the liver and kidney. 2. The accumulated metals in the liver supernatant fractions were present as Zn- and Cu-binding proteins of the same properties as that of metallothionein (MT) induced by cadmium (Cd) injections. 3. The affinity of Zn, Cu and Cd ions to the metal-binding protein was in the decreasing order of Cu, Cd and Zn. 4. The Xenopus MT induced by Cd was unstable and disrupted easily to give two peaks as if the MT consists of two isometallothioneins.     

Dietary cadmium induces histopathological changes despite a sufficient metallothionein level in the liver and kidneys of the bank vole (Clethrionomys glareolus)

The objective of this study was to correlate hepatic and renal cadmium (Cd) accumulation, Cd-binding capacity of metallothionein (MT) and lipid peroxidation with the tissue injury in the male bank voles raised under short (8 h light/16 h dark) and long (16 h light/8 h dark) photoperiods that affect differently Cd accumulation and MT induction in these rodents. The animals were exposed to dietary Cd (0, 40 and 80 microg/g) for 6 weeks. The accumulation of Cd in the liver and kidneys appeared to be dose-dependent in bank voles from the two photoperiod groups; however, the short-photoperiod animals exhibited significantly higher concentrations of Cd in both organs than the long-photoperiod bank voles. Cd-Binding capacity of MT in the liver and kidneys of bank voles from the long photoperiod was sufficiently high to bind and detoxify all Cd ions, while in the animals fed 80 microg Cd/g under the short photoperiod, the concentrations of Cd in both organs exceeded (by about 10 microg/g) the MT capacity. However, similar histopathological changes in the liver (a focal hepatocyte swelling and granuloma) and kidneys (a focal degeneration of proximal tubules) occurred in Cd-80 bank voles from the two photoperiods. Likewise, in either photoperiod group, dietary Cd brought about a similar, dose-dependent decrease in the hepatic and renal lipid peroxidation, which paralleled closely that of the iron (Fe) concentrations. These data indicate that: (1) MT does not protect the liver and kidneys against Cd-induced injury in the bank vole exposed to the higher level of dietary Cd; and (2) lipid peroxidation cannot be responsible for the tissue damage. It is hypothesized that dietary Cd produces histopathological changes indirectly, through depressing the tissue Fe and Fe-dependent oxidative processes.     

Trace Elements and Metallothionein in Liver and Kidney of <Emphasis Type="Italic">Felis catus</Emphasis>

Trace metals such as Zn, Cu, and Fe are essential for life; differently, no biochemical function is known for Cd. Changes in dietary metal concentrations can cause deficiency or toxicity. Studies on trace elements in cat are lacking. This paper aimed to analyze Zn, Cu, Fe and Cd concentrations in liver and kidney of pathological domestic cat and to isolate metallothionein (MT) in these tissues. It was not possible to explore a possible correlation between metal concentrations and pathologies because the incidence for each of them was too low. Fe was the most abundant metal; in particular, the liver accumulates average Fe concentrations one order of magnitude higher than Zn and Cu, ranging from 66.75 and 1,444.23 μg/g. Significantly, higher levels of Fe were found in the liver of elder animals. Zn concentrations varied between 26.31 and 84.78 μg/g in the liver whereas in the kidney, ranged between 7.69 and 71.15 μg/g. Cu concentrations were between 2.37 and 112.91 μg/g in liver and between 2.12 and 9.85 μg/g in kidney. Cd was the least abundant metal with the exception of the kidney of the oldest cats where it reached a maximum of 13.71 μg/g. Gel-filtration metal distribution profiles from cytosolic extracts revealed the presence of Cd, Cu, Zn thioneins either in the liver or in the kidney. Because tissue samples were taken from pathological cats from different breed and age, care must be taken to use these data as a baseline profile of trace elements in healthy animals. Our results are indicative that for some specimens the feed levels of Fe and Cu could be higher than the optimal dietary intake and in few cats, there was also an exposure to Cd that was counteracted by MT biosynthesis.     

Dietary pharmacological or excess zinc and phytase effects on tissue mineral concentrations, metallothionein, and apparent mineral retention in the newly weaned pig

Feeding pharmacological zinc (Zn) to weaned pigs improves growth, and dietary phytase improves P and Zn availability. Metallothionein (MT) increases in the duodenum, kidney, and liver of pigs fed 1000 mg Zn/kg with phytase or 2000 mg Zn/kg with or without phytase when fed for 14 d postweaning. The goal of this study was to determine the effects of feeding pharmacological Zn and phytase on tissue minerals, MT, mineral excretion, and apparent retention. Twenty-four newly weaned pigs (20 d; 7.2 kg) were individually fed twice daily, a basal diet supplemented with 0, 1000, or 4000 mg Zn/kg as Zn oxide, without or with phytase (500 phytase units [FTU]/kg) for 14 d, followed by a basal diet (100 mg Zn/kg) without phytase for 7 d. Pigs fed 4000 mg Zn/kg without phytase had higher (p=0.01) plasma, hepatic, renal Zn, renal Cu, and hepatic, renal, and jejunal MT than pigs fed the basal diet or 1000 mg Zn/kg. Duodenal MT was higher (p=0.0001) in pigs fed 1000 and 4000 mg Zn/kg than in pigs fed the basal diet. In pigs fed 1000 and 4000 mg Zn/kg, Zn loading occurred during the first 11 d of supplementation; by d 14, excess Zn was being excreted in the feces.     

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. Accepted: 27 November 1999