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241.
Homeostatic systems for essential and non-essential metals create the cellular environments in which the correct metals are acquired by metalloproteins while the incorrect ones are somehow avoided. Cyanobacteria have metal requirements often absent from other bacteria; copper in thylakoidal plastocyanin, zinc in carboxysomal carbonic anhydrase, cobalt in cobalamin but magnesium in chlorophyll, molybdenum in heterocystous nitrogenase, manganese in thylakoidal water-splitting oxygen-evolving complex. This article reviews: an intracellular trafficking pathway for inward copper supply, the sequestration of surplus zinc by metallothionein (also present in other bacteria) and the detection and export of excess cobalt. We consider the influence of homeostatic proteins on selective metal availability. 相似文献
242.
Dobrovoljc K Falnoga I Bulog B Tusek-Znidaric M Scancar J 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,135(3):285-294
The presence of metallothionein (MT) and the subcellular distribution of copper, zinc and cadmium were investigated in livers of two neotenic salamanders, Proteus anguinus and Necturus maculosus. In P. anguinus, caught in the wild, hepatic MTs were present as a single isoform of (Zn, Cu, Cd)-thioneins, whose molecular weight was estimated to be approximately 12000 by size exclusion chromatography. The percentage of zinc and cadmium was higher in the cytosol and of copper in the pellet. Cytosolic cadmium was almost exclusively associated with MTs (80%), while zinc and copper were also present in the regions of higher-molecular weight proteins. In laboratory bred N. maculosus, MTs were isolated from the liver cytosol and extract of the pellet as (Cu, Zn)- and (Zn, Cu)-thioneins, respectively. According to the low amount of copper extracting from liver pellets of N. maculosus, the presence of water insoluble aggregated forms of Cu-thioneins should be checked in further investigations. 相似文献
243.
Craig S Overnell J 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,134(3):311-317
An adult squid Loligo forbesi had the following metals in its liver/digestive gland: Mn, Fe, Ni, Zn, Cu, As, Cd, Ba and Pb in the range of 1-110 ppm wet wt. Adult mantle muscle, adult eyes, eggs and hatchlings contained a lesser number of these metals at concentrations above 1 ppm. Chromatographic analysis of non-heat-treated cytosols (in the presence of 5 mM 2-mercaptoethanol) gave no evidence for the presence of copper- or zinc-containing fractions with the molecular weights of mollusc metallothioneins in any of the above tissues. Copper and Zn were bound to either the particulate fraction or to very low molecular weight species. 相似文献
244.
Lieb B 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,134(1):131-137
Metallothioneins (MTs) are small soluble proteins ubiquitously expressed in animals and plants. Different isoforms are present in deuterostomes and protostomes. They do not differ greatly in primary structure, but are clearly distinguishable. Here, I present the gene and the complete cDNA of a novel MT from the mollusk Megathura crenulata. This protein is closely related to the Cu-inducible MTs of the vineyard snail Helix pomatia, but has also some minor sequence features typical of Cd-inducible isoforms of H. pomatia and other molluscs. Overall, the deduced primary structure is similar to the known molluscan MTs, but in addition possesses an insertion of 5 amino acids not found in any other molluscan MTs, protostomic or deuterostomic MTs. In addition, a pentapeptide insertion, characteristic of mammalian MT-3 is present but it lacks the functional tetrapeptide CPCP within the beta-region of those MT-3 proteins that are known to suppress neuronal growth processes. The M. crenulata MT is a novel form of MT in comparison to all other known MTs. Possible functional aspects for this new MT are discussed. 相似文献
245.
Enhancement of MT synthesis by leptin in fasted mice 总被引:4,自引:0,他引:4
Kondoh M Tsukahara R Kuronaga M Higashimoto M Takiguchi M Sato M 《Life sciences》2002,71(20):2425-2433
It is known that metallothionein (MT) synthesis occurs in the liver in various stressful situations such as immobilization and fasting. However, the mechanism of MT synthesis in stressful situations is not fully understood. In this study, we examined the involvement of leptin, the obese gene product, in MT synthesis induced by fasting stress. Despite an increase in hepatic MT levels induced by 24-hr fasting in wild-type mice, both wild-type and MT-null mice showed decreases in plasma leptin levels after 24 hr of fasting. Hepatic MT levels increased to levels comparable with that in control mice in ICR, C3H, 129Sv and Balb/c mice fasted for 24 hr, and plasma leptin levels decreased significantly. Repetition of fasting and feeding in turn every 24 hr caused a gradual decrease in hepatic MT levels after the fasting period. In contrast, the reduced plasma leptin levels increased after the fasting period with repetition of fasting-feeding cycles. The findings indicate that there is an adaptation to starvation. On the other hand, subcutaneous leptin infusion in fasted mice via an osmotic pump resulted in increases in hepatic MT levels compared to the levels in vehicle-treated mice after 24 hr of fasting. Only leptin infusion had no effect on hepatic MT levels. These results suggest that MT synthesis in fasting stress is not correlated with decrease in plasma leptin levels but that leptin itself is a potent inducer of MT in a fasting situation. 相似文献
246.
Ceratto N Dondero F van de Loo JW Burlando B Viarengo A 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2002,131(3):217-222
Metallothionein (MT) is a ubiquitous, metal-inducible protein with an important role in the homeostasis and in the detoxification of heavy metals. This work reports the cloning and sequencing of a MT gene encoding a MT isoform (MT20-IIIa) in the mussel Mytilus galloprovincialis Lam, a lamellibranch mollusc known to accumulate and to detoxify large amounts of metal. The MT gene, lacking the 5' promoter region, is 1865 bp long and has a tripartite structure consisting of three exons and two introns. The putative open reading frame (ORF) encodes a polypeptide of 72 amino acids, which corresponds to the MT-I class, type 2 family (http://www.unizh.ch/~mtpage/classif.html). The structure of the gene and the putative MT20-III protein have been compared with those of other species. The putative biological significance of the differences at the amino acid level among the different MTs is discussed. 相似文献
247.
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
248.
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
249.
250.
Although the analysis of metallothionein (MT) by radioimmunoassay (RIA) is not a common technique, its use is preferred over
other methods since it offers the advantages of sensitivity and specificity. In this paper we present data on the basal levels
of MT in rat tissues and physiological fluids of female Sprague-Dawley rats. The mean basal MT concentrations of the following
organs and fluids were determined by RIA to be: liver (9.8 μg/g), kidney (68 μ/g), brain (0.8 μg/g), spleen (1.0 μg/g), heart
(5.4 μg/g), plasma (11 ng/ml), and urine (200–300 μg/g creatinine). Following subcutaneous exposure to inorganic mercury (0.2
μmol/kg/d, 5 d a week for up to 4 wk), the metal accumulated primarily in the kidney. There was also a simultaneous accumulation
of zinc in the liver and of zinc and copper in the kidney. Induction of MT did take place in liver, kidney, brain, and spleen.
No increases in the MT contents of blood and urine were noted. The excess zinc and copper in the kidney of exposed animals
were found to be associated predominantly with MT. No overt signs of mercury toxicity were noted in these animals and the
incidence of proteinurea was nil. The data are discussed with reference to methods of MT determination in animal tissues and
in relation to mercury metabolism and toxicity. 相似文献