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261.
Takeshi Minami Hideki Matsubara Masayuki O-higashi Noriko Otaki Masami Kimura Kanenobu Kubo Nobuo Okabe Yuko Okazaki 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,685(2):369
Metallothionein (MT) isoforms from various liver tissues were separated with capillary zone electrophoresis (CZE) using a polyacrylamide-coated tube at neutral pH. The electrophoresis was performed on MT-1 and MT-2 purified from mouse, rat, rabbit and human livers. The retention times of mouse and rat MT-1 coincided, while the retention times of rabbit and human MT-1 were longer. The retention times of MT-2 purified from the four sources were the same. MT-1 and MT-2 separated more definitely with N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES)-Tris buffer (25 mM, pH 7.4) than with N-tris(hydroxymethyl)methyl-3-aminopropane sulfonic acid (TAPS)-Tris buffer (25 mM, pH 7.7) or with N-(2-acetamido)iminodiacetic acid (ADA)-Tris buffer (25 mM, pH 7.4). In addition, liver MT isoforms prepared from Zn- or Cd-administered mice could be separated. 相似文献
262.
263.
Sodium selenite was administered to rats before, after, and simultaneously with mercuric chloride. In all animal groups, mercury
was administered intravenously in doses of 0.5 mg/kg every other day for two weeks. Selenium was given intragastrically either
in a single dose of 7.0 mg Se/kg or in repeated doses of 0.1 mg Se/kg every day for weeks. It was demonstrated that, depending
on the administration schedule, selenium induced significant changes in the binding of mercury by soluble fraction proteins
both in the kidneys and in the liver. In every exposure, the mercury content decreased mainly in the low-molecular weight
proteins, and the level of metallothionein-like proteins was diminished in the both organs. In the kidneys, the mercury content
showed a correlation with the level of metallothionein (r=0.78). Amounts of mercury below 10 μg/g kidney do not stimulate metallothionein biosynthesis in this organ. A distinct interaction
effect was observed in the case of a simultaneous administration of equimolar amounts of both the metals in question. 相似文献
264.
265.
制备一定量的Cd、Zn兔肝金属硫蛋白(metalothionein,MT),然后脱掉其中的金属,获得不含金属的硫蛋白(apoMT).用一价金属CuCl或AgNO3以5.81的金属蛋白摩尔比与apoMT结合,将其β结构域用金属饱和,在37℃,pH7.0下用枯草杆菌蛋白酶水解掉未结合金属的α结构域,获得Cu(Ⅰ)、Ag(Ⅰ)结合的兔肝MT-I、MT-Ⅱ的β结构域.通过HPLC、羧甲基化后的SDS-PAGE、氨基酸组成分析、金属定量、N末端分析和紫外扫描等鉴定,证明确实得到了N末端为Met,分子量3000左右,金属蛋白摩尔比为5~5.51的MTβ结构域,其氨基酸组成与理论值基本相符 相似文献
266.
单细胞蓝藻(Synechococussp.PCC7942)以50μmol/LZn2+诱导8d后收集,破碎取上清液经凝胶过滤、离子交换层析及反相HPLC纯化得到类金属硫蛋白,产率为每升培养液收集1.5g鲜藻,得2.5mg纯品.其单体分子量为8750,N未端测定为缬氨酸,氨基酸组成分析得每分子(56个氨基酸)含10个半胱氨酸,疏水氨酸较多,且含有芳香族氨基酸,原子吸收光谱测得每分子蛋白结合4个二价金属.以上表明,该种类金属硫蛋白与哺乳动物金属硫蛋白结构差异很大,可能只是一种进化上的趋同. 相似文献
267.
Metallothionein Induction in Neonatal Rat Primary Astrocyte Cultures Protects Against Methylmercury Cytotoxicity 总被引:2,自引:0,他引:2
Abstract: Metallothionein (MT) protein and mRNA levels were monitored following exposure of rat neonatal primary astrocyte cultures to methylmercury (MeHg). MT-I and MT-II mRNAs were probed on northern blots with an [α-32 P]dCTP-labeled synthetic cDNA probe specific for rat MT mRNA. MT-I and MT-II mRNAs were detected in untreated cells, suggesting constitutive MT expression in these cells. The probes hybridize to a single mRNA with a size appropriate for MT, ∼550 and 350 bp for MT-I and MT-II, respectively. Expression of MT-I and MT-II mRNA in astrocyte monolayers exposed to 2 × 10−6 M MeHg for 6 h was increased over MT-I and MT-II mRNA levels in controls. Western blot analysis revealed a time-dependent increase in MT protein synthesis through 96 h of exposure to MeHg. Consistent with the constitutive expression of MTs at both the mRNA level and the protein level, we have also demonstrated a time-dependent increase in MT immunoreactivity in astrocytes exposed to MeHg. The cytotoxic effects of MeHg were measured by the rate of astrocytic d -[3 H]aspartate uptake. Preexposure of astrocytes to CdCl2 , a potent inducer of MTs, completely reversed the inhibitory effect of MeHg on d -[3 H]aspartate uptake that occurs in MeHg-treated astrocytes with constitutive MT levels. Associated with CdCl2 treatment was a time-dependent increase in astrocytic MT levels. In summary, astrocytes constitutively express MTs; treatment with MeHg increases astrocytic MT expression, and increased MT levels (by means of CdCl2 pretreatment) attenuate MeHg-induced toxicity. Increased MT expression may represent a generalized response to heavy metal exposure, thus protecting astrocytes and perhaps also, indirectly, juxtaposed neurons from the neurotoxic effects of heavy metals. 相似文献
268.
Eva Freisinger 《Inorganica chimica acta》2007,360(1):369-380
Metallothioneins (MTs) are ubiquitous low molecular mass, cysteine-rich proteins with the ability to bind d10 metal ions in the form of metal-thiolate clusters. In contrast to the vertebrate forms, knowledge about the properties of members of the plant metallothionein family is still scarce. The amino acid sequences of plant MTs are distinctively different to the sequences of other MT species. The protein under investigation, Musa acuminata (banana) MT3, belongs to the plant MT fruit-specific p3 subfamily. With a total of 10 cysteine residues, MT3 features a cysteine content and percentage that is more comparable to fungal and prokaryotic MTs than to the well characterized mammalian iso-forms. The gene sequence encoding MT3 was cloned into a suitable vector and the protein was recombinantly overexpressed in Escherichia coli. MT3 is able to coordinate a maximum of four divalent d10 metal ions under the formation of metal-thiolate clusters. The hitherto unknown spectroscopic behavior of MT3 in combination with the metal ions Zn2+, Cd2+, Pb2+, and Hg2+ will be presented and gives rise to the existence of a weaker metal ion coordination site. The pH stability of the investigated zinc and cadmium clusters is comparable to the values found for other plant metallothioneins though significantly lower than for the mammalian iso-forms. Possible metal-thiolate cluster structures will additionally be discussed. 相似文献
269.
Metallothioneins are ubiquitous low molecular mass, cysteine-rich proteins with an extraordinary high metal ion content. In
contrast to the situation for the vertebrate forms, information regarding the properties of members of the plant metallothionein
family is still scarce. We present the first spectroscopic investigation aiming to elucidate the metal ion binding properties
and metal thiolate cluster formation of the Tricium aestivum (common wheat) early cysteine-labeled plant metallothionein (Ec-1). For this, the protein was overexpressed recombinantly in Escherichia coli. Recombinant Ec-1 is able to bind a total of six divalent d
10 metal ions in a metal thiolate cluster arrangement. The pH stability of the zinc and cadmium clusters investigated is comparable
to stabilities found for mammalian metallothioneins. Using cobalt(II) as a paramagnetic probe, we were able to show the onset
of cluster formation taking place with the addition of a fourth metal ion equivalent to the apo protein. Limited proteolytic
digestion experiments complemented with mass spectrometry and amino acid analysis provide clear evidence for the presence
of two separate metal thiolate clusters. One cluster consists of four metal ions and is made up by a part of the protein containing
11 cysteine residues, comparable to the situation found in the mammalian counterparts. The second cluster features two metal
ions coordinated by six cysteine residues. The occurrence of the latter cluster is unprecedented in the metallothionein superfamily
so far.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This article is dedicated to Prof. Bernhard Lippert on the occasion of his 60th birthday. 相似文献
270.
Studies have shown that metallothionein (MT) may play an important role in modulating the activity of certain Zn-regulated enzymes under various oxidoreductive conditions by either donating or removing Zn. To better determine the role of MT in interprotein metal transfer, we describe a procedure that uses stable isotopically enriched (67)Zn(7) metallothionein 2 ((67)Zn(7)-MT-2) to quantitatively determine the stoichiometry of transfer of Zn from the protein to a recipient apo-metalloenzyme, apo-carbonic anhydrase (apo-CA) by directly coupled ion exchange high-performance liquid chromatography inductively coupled plasma mass spectrometry. Quantitatively, the transfer of (67)Zn was consistent with the enzymatic activation of the apo-enzyme as judged by its esterase activity and ability to cleave p-nitrophenyl acetate. Maximum enzyme activation occurred at an MT-2:apo-CA molar ratio of 1, implying the release of a single atom of Zn from MT-2. Preincubation of (67)Zn(7)-MT-2 with an excess of oxidized glutathione (GSSG) increased metal donation fourfold, whereas reduced glutathione (GSH) inhibited donation by approximately 50%. By using multiple recipient and donor proteins having different stable isotopic signatures, the technique has the potential for quantitatively studying the kinetic and thermodynamic aspects of Zn transfer between numerous competing ligands in vitro, an important first step toward understanding the regulatory role of this metal in protein functioning and cellular metabolism in vivo. 相似文献