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PubMed1987

Induction of zinc-thionein by estradiol and protective effects on inorganic mercury-induced renal toxicity.

The castrated or unoperated male rats received an intravenous injection of HgCl2 at a dose of 0.7 mg/kg of body weight (b.w.) after pretreatment with 30% ethanol or estradiol dissolved in 30% ethanol at a dose of 0.5 mg/kg b.w. subcutaneously twice a day for six consecutive days. Renal total protein, gamma-GTP and K excretion in the rats treated with Hg and estradiol were significantly lower than the corresponding values in the rats treated with Hg alone, suggesting that pretreatment with estradiol ameliorates the renal toxicity of Hg in male rats. Pretreatment with estradiol significantly increased Hg and Hg-thionein(Hg-MT) concentrations in the renal cortex of the animals treated with Hg, though in the liver this agent did increase the Hg-MT without elevation of Hg concentration. Treatment with estradiol alone (0.5 mg/kg, s.c., twice a day, for six consecutive days) significantly increased the zinc-thionein (Zn-MT) concentration in the kidney and liver. Simultaneous treatment with 10(-5) M estradiol and Hg in human amniotic-fluid cells caused a significant increase in the uptake of Hg and the synthesis of Hg-MT, suggesting that estradiol may directly stimulate an accumulation of Hg into the cells and the synthesis of Hg-MT. Together, all of the above findings suggest that pretreatment with estradiol may increase the uptake of Hg, which in turn leads to the increase in the Hg-MT concentration. The induction of Zn-MT by pretreatment with estradiol may account for the protective effect of estradiol on Hg-induced renal toxicity.

Animals↗
PubMed1983

Reconstitution of stellacyanin as a case of direct Cu(I) transfer between yeast copper thionein and 'blue' copper apoprotein.

It was of interest to examine whether yeast Cu-thionein could be used to transfer the thiolate bound copper directly into the copper binding site of 'blue' apoproteins which contain free thiol groups. In particular apo-stellacyanin was used in the present study and it was found to be able to accept Cu(I) from yeast Cu-thionein, without any detectable unspecific Cu(II) intermediate, both aerobically and anaerobically.

Apoproteins↗
PubMed1996

Stable thiyl radicals in dried yeast Cu(I)6-thionein.

It was of interest to obtain long-lived thiyl radicals embedded in organic matrices. Solid thiol compounds including penicillamine, glutathione, and cysteine were UV irradiated under anaerobic conditions at 293 K for 60 min. The formed radicals were identified by electron paramagnetic resonance (EPR) (g = 2.0265 +/- 0.0015) at 293 K as thiyl radicals. The blue-colored radical species were subjected to reflection spectrometry (lambda max = 601 +/- 3 nm). The color and the EPR signal remained unchanged for six months. At the same time, the UV irradiation of lyophilisized yeast Cu(I)6-thionein generated stable EPR detectable thiyl was seen when the Cu(I)-thiolate was used. No EPR detectable thiyl radicals radicals at a g-value of 2.026 +/- 0.001. Unlike irradiated cysteine, a five times higher concentration of thiyl radicals were measured in the Cu(I)-thiolates of penicillamine, glutathione, and thiophenole, indicating that the hexanuclear copper arrangement in Cu(I)-thionein is most suitable for both the formation and stabilization of this sulfur radical species.

Carrier Proteins↗
PubMed1994

Transient thiyl radicals in yeast copper(I) thionein.

In an EPR study employing yeast copper(I) thionein, GSH and Cu-GSH it was shown that thiyl radicals could be successfully generated from the thiolate sulfur via oxidation by photochemically formed superoxide at 77 K. The g-value was 2.036. Essentially no EPR detectable copper(II) was monitored under the experimental conditions, indicating that the oxidation reduction process is restricted to the thiolate sulfur. The Cu(I)-thiolate chromophores remained fully intact as deduced from chiroptical and luminescence measurements. Thus, copper thionein is supposed to be actively involved in the scavenging of oxygen free radicals by a reversible thiolate oxidation reduction cycle. The coordinated Cu(I) seems to serve as a prominent candidate to stabilize the transiently formed thiyl radical.

Carrier Proteins↗
PubMed1989

Copper-thionein in melanoma.

The phenomenon of an elevated copper concentration in melanoma tumors was examined. It was demonstrated that 50-60% of total tissue copper is associated with metallothionein. The amino acid composition, electronic absorption and fluorescence were identical to that of the many known vertebrate Cu-thioneins. The immunological identification of melanoma tissue metallothionein was successful. The elevated Cu-thionein concentration in melanoma tumor tissue is not yet understood. It appears to be a common concept that in most tumors transient changes of the copper status parallel the metallothionein levels.

Amino Acids↗
PubMed1980

Rat kidney metallothionein induced by injection of Cd-thionein: Changes of chromatographic properties with time and their relation to copper content and kidney dysfunction.

Cadmium (Cd)-thionein was injected i.p. into adult rats to try to establish the relation between copper (Cu) content in the kidneys and its effect on the properties of metallothionein induced in the kidneys. Elution profiles of the re-synthesized kidney metallothionein changed with time after injection both on a Sephadex and on a gel permeation column (TSK GEL SW3000). The changes were correlated with Cu content in the kidneys caused by kidney dysfunction upon injection of Cd-thionein.

Animals↗
PubMed1988

Release of copper from yeast copper-thionein after S-alkylation of copper-thiolate clusters.

Our knowledge on the release of copper from Cu-thionein in biological systems is limited. Other than oxidative cleavage or direct transfer, the possibility of an alkylation mechanism seemed attractive. Iodoacetamide and methyl methanesulphonate were successfully employed to alkylate the Cu-thiolate sulphur atom of homogeneous Cu(I)-thionein from yeast. The alkylation caused a weakening of the Cu-S bonding, which led to the release of copper. After equilibrium dialysis a proportion of the released copper was found in the dialysis buffer. When iodoacetamide was used carboxymethylcysteine was detected in the protein hydrolysate. A 10-fold molar excess over cysteine was sufficient for complete alkylation, which could be conveniently monitored by c.d. at 328 and 359 nm. The reaction proceeded under both aerobic and anaerobic conditions. E.p.r. measurements of Cu2+ revealed unequivocally the complete cleavage of the Cu-thiolate bonding in less than 5 h. It is possible that this mode of copper release might be of relevance to the molecular transport of this biochemically important transition metal.

Alkylation↗
PubMed1998

Modulation of DNA binding of a tramtrack zinc finger peptide by the metallothionein-thionein conjugate pair.

The ability of metallothionein (MT) to modulate DNA binding by a two-finger peptide of Tramtrack (TTK), a CCHH zinc transcription factor, was investigated using metal-bound and metal-deficient forms of rabbit MT-2 and the TTK peptide. Thionein inhibited DNA binding by zinc-bound TTK, and Zn-MT restored DNA-binding by zinc-deficient apo-TTK. "Free" zinc at low concentrations was as effective as Zn-MT in restoring DNA binding by apopeptide but was inhibitory at concentrations equal to zinc bound to 2 mol eq and higher of Zn-MT. Substitution of cadmium for zinc reduced the affinity of the peptide for its DNA binding site. This effect was reversed by incubation with Zn-MT. The circular dichroic spectra of the TTK peptide indicated that zinc removal resulted in loss of alpha-helical structures, which are sites of DNA contact points. Reconstitution with cadmium resulted in stoichiometric substitution of 2 mol of Cd/mol of peptide but not recovery of alpha-helical structures. Incubation of Cd-TTK with Zn-MT restored the secondary structure expected for zinc-bound TTK. The ability of Zn-MT and thionein to restore or inhibit DNA-binding by TTK was associated with effects on the metallation status of the peptide and related alterations in its secondary structure.

Animals↗
PubMed1979

Cadmium, an effector in the synthesis of thionein.

Cadmium can elicit the synthesis of thionein in liver cells independent of tissue-organ interactions. The metal diffuses across the plasma membrane and is partitioned between subcellular components in a time dependent manner such that thionein synthesis responds to levels of nonspecifically and specifically bound cytoplasmic metal. Cadmium appears to function at the transcriptional level, and the metal may act to increase the pool of specific m-RNA's.

Animals↗
PubMed1982

Cadmium inhibition of in vitro hepatic oxidative drug metabolism in the rat: comparison between ionic cadmium and cadmium-thionein.

The effectiveness of cadmium added in vitro in inhibiting the microsomal oxidative metabolism of ethylmorphine or aniline in rat hepatic microsomes was markedly decreased if the metal was added as cadmium-thionein when compared to ionic cadmium. These data are consistent with the hypothesis that cadmium thionein is less active biologically than ionic cadmium.

Aniline Hydroxylase↗
PubMed1981

Effects of methylmercury on zinc-thionein levels of rat liver.

The induction of metallothionein synthesis by administration of methylmercury chloride as studied. A repetitive sc dose of methylmercury chloride to rats in amounts of 10 mg/kg/day for 3 days produced profound hypozincemia and 3-fold increase in hepatic zinc bound to metallothionein by the initial 24 h. The incorporation of 35S-cysteine into hepatic metallothionein was about 4 times larger for rats treated with methylmercury, which was comparable with it for rats treated with cadmium, than for control rats. These results suggest the induction of de novo synthesis of metallothionein by administration of methylmercury, although methylmercury was found to be unable to bind to produced metallothionein both in vivo and in vitro. A stress produced by methylmercury administration appears to be involved in the induction of hepatic zinc-thionein by methylmercury, through its mechanism is not clear.

Animals↗
PubMed2003

The Cu(I)(7) cluster in yeast copper thionein survives major shortening of the polypeptide backbone as deduced from electronic absorption, circular dichroism, luminescence and( 1)H NMR.

Owing to the frustrating experience of not being able to obtain crystalline yeast Cu(I)(7) -metallothionein, thereby allowing elucidation of the X-ray structure, truncated forms were prepared to facilitate possible crystallization. The mobile remnants at either the N- or C-terminal end of the polypeptide chain were omitted. In parallel with the crystallization efforts, it was of interest to examine the degree to which the shortening of the protein portion might affect the intactness of the Cu(I)(7) -thiolate cluster, thereby hampering their use as structural models for the intact protein. (1)H two-dimensional NMR spectroscopy at 800 MHz was performed on the intact wild-type yeast Cu(7)-thionein and on two truncated forms (peptide(-1-40) and peptide(5-40)). The NMR spectral data reveal, regardless of the length of the polypeptide chain, that the spin patterns were fully preserved with all relevant NOEs. The corresponding calculated structures were virtually identical. All other spectrometric properties, including circular dichroism, luminescence and electronic absorption, allowed the same conclusion. Minor differences were observed in the chiroptic and luminescent measurements. Interestingly, however, the resistance towards oxygen was progressively diminished with decreasing length of the polypeptide backbone. The half-life of the luminescence of the wild-type protein was 48 h while the luminescence of the shortest peptide levelled off within 24 h.

Amino Acid Sequence↗
PubMed1977

Copper thionein in the kidneys of copper-poisoned sheep.

A study has been made of the distribution of copper in the kidneys of copper-poisoned sheep, containing up to 240 microgram copper/g fresh cortex. About 64% of the copper in the cortex was present in the cytosol and 75% of this occurred in a form with molecular weight of approx. 12 000. This was partially purified by gel filtration on Sephadex G-75 and Bio-Gel P.10 and ion exchange chromatography on DEAE Sephadex A-25 to give three sub-fractions, which also contained zinc. The amino acid composition, copper content and chromatographic behaviour of these proteins indicated that they were copper-thioneins. No significant amounts of the proteins were detected in the plasma or erythrocytes of the copper-poisoned sheep when they were undergoing the haemolytic crisis typical of this syndrome. It is concluded that metallothionein constitutes the major copper-binding protein in the kidneys of copper-poisoned sheep. However the rapid accumulation of the protein in the kidney, and the development of kidney damage, are unlikely to have arisen from the release of the intact copper-protein from the liver and its transport via the blood to the kidneys.

Amino Acids↗
PubMed1977

Isolation of a non-thionein copper-binding protein from liver of copper-injected rats.

1. The characterization of a low molecular weight, non-thionein, Cu-binding protein isolated from rat liver is reported. The protein was isolated following chronic administration of Cu(NO3)2 using a combination of Sephadex G75 and Sephadex DEAE A-25 chromatography. The protein did not bind to fully equilibrated Sephadex DEAE which formed the basis of the isolation procedure. 2. The final protein pereparation was found to be homogenous by a variety of electrophoretic techniques and was distinguished from metallothionein on the basis of its behaviour on ion exhcange and electrophoretic systems, spectral properties, and amino acid composition and metal content. It contains 6.8% cysteine and was found to bind Cu in a ration of 1.5:1 based on a molecular weight of 11 000. 3. These results confirm the necessity to use techniques other than gel filtration alone to obtain adequate separation of low molecular weight metal-binding protein fractions.

Amino Acids↗
PubMed1984

Distribution of cadmium after oral administration of cadmium-thionein to mice.

Distribution of Cd was compared after oral administration of either Cd ions or Cd-thionein (Cd-TH). Mice received 0.5 mg Cd/kg, po as CdCl2 in saline, CdCl2 in control rat liver homogenate, Cd-TH in saline, Cd-TH in liver homogenate, or liver homogenate from Cd-treated rats. In all cases, 85-90% of the Cd dose was present in feces within 24 hr. However, in groups receiving CdCl2, more Cd was found in feces on Days 2 and 3 in comparison to those receiving Cd-TH. All treatments resulted in lower levels of Cd in liver than in kidney. In addition, tissue levels indicate that less Cd was absorbed when rats received Cd-TH in saline than CdCl2 in saline. Cd-TH added to liver homogenate or liver homogenate containing Cd-TH increased the absorption of Cd resulting in renal Cd levels similar to those in mice receiving CdCl2 in saline. The kidney/liver Cd concentration ratio (9) was the same for Cd-TH in all three media. Although Cd-TH gave much higher kidney/liver Cd ratios than CdCl2 (9 vs 2), renal Cd concentrations were the same or lower than after CdCl2 treatments. Results indicate that the high kidney/liver Cd ratio after Cd-TH treatment versus CdCl2 is due to lower concentrations of Cd in liver rather than marked increases in renal Cd levels. Heating of Cd-TH did not result in lower amounts of Cd in kidney. While the chemical form of Cd administered affects the absorption and distribution of Cd, the amount of Cd reaching the kidney after Cd-TH administration is similar to that after CdCl2 administration.

Administration, Oral↗
PubMed1980

Induction of zinc-thionein in rat liver and kidneys by zinc loading as studied at isometallothionein levels.

Zinc acetate was injected i.p. into female rats to try to clarify the detailed induction and degradation pathways of zinc-thionein (Zn-th) at isometallothionein levels in liver and kidneys. Injected zinc in serum decreased with the induction of Zn-th in the liver and kidneys, and the amounts of Zn-th in both tissues attained maxima 24 h after injection. The relative ratios of isometallothioneins changed with time in both tissues. The changes are compared with those of cadmium (Cd) loading.

Animals↗
PubMed1986

Comparative induction of hepatic zinc-thionein and increase in tissue calcium by bacterial endotoxin in endotoxin-sensitive (C3H/HeN) and endotoxin-resistant (C3H/HeJ) mice.

Induction of zinc-thionein (Zn-Th) by endotoxin was studied in mice using an endotoxin-sensitive C3H/HeN strain and an endotoxin-resistant C3H/HeJ strain to find a relation between the sensitivity of these strains to endotoxin and the inducibility of hepatic Zn-Th by the endotoxin. Both strains of female mice were injected with endotoxin at two doses and the increase in hepatic Zn-Th levels was examined after 24 h. At the lower dose (0.25 mg/kg body weight), C3H/HeJ mice induced Zn-Th at a markedly lower level than C3H/HeN mice. However, both strains exhibited a comparable amount of Zn-Th when a higher dose (10 mg/kg body weight) of endotoxin was used. A parallel increase in hepatic calcium concentration was observed with the induction of hepatic Zn-Th in both strains. The injection of a spleen supernatant fraction from C3H/HeJ mice into C3H/HeN mice did not reduce the Zn-Th induction by endotoxin in C3H/HeN mice.

Animals↗
PubMed1987

Chemical form-dependent induction of hepatic zinc-thionein by arsenic administration and effect of co-administered selenium in mice.

Four arsenic compounds (m-arsenite, arsenate, methylarsonate (MMA), and dimethylarsinate (DMA) were administered to mice, either orally or by intraperitoneal injection, and the amounts of induced hepatic zinc-thionein (Zn-Th) were determined to investigate the chemical form dependency in metallothionein induction by arsenic. Several mice died within 24 h following intraperitoneal injection. The toxicity estimated from the lethality was in the order of m-arsenite greater than arsenate much greater than DMA approximately equal to MMA. Although all 4 arsenic compounds more or less induced Zn-Th following intraperitoneal injection, the dose of inorganic arsenic compounds observed to cause induction was one order lower than that of organic arsenic compounds. The induction of hepatic Zn-Th was also observed following oral administration, and inorganic arsenic compounds were again found to be more effective inducers via this route. To study the interactions of m-arsenite and selenite with regard to the amounts of Zn-Th induced, the two compounds were co-administered intraperitoneally. The amount of hepatic Zn-Th induced by the co-administration was one-fifth of that observed after selenite administration, and was almost the same as that after m-arsenite injection. Namely, when co-administered m-arsenite had the effect of lowering the level of Zn-Th induced following selenite administration, but the converse phenomenon was not observed.

Animals↗