金属对金属全髋关节置换术后体内金属离子对机体的影响

金属对金属全髋假体由于其具有良好的活动度因而被广泛应用全髋关节置换,但是由于金属对金属全髋假体置换术后可以产生大量的钴铬金属离子而使机体内血液尿液中金属离子水平升高,而金属离子水平升高后可能会对机体产生不利影响,本文就金属对金属全髋假体置换术后对机体的影响作一综述。     

金属对金属全髋关节置换术后体内金属离子对机体的影响

金属对金属全髋假体由于其具有良好的活动度因而被广泛应用全髋关节置换,但是由于金属对金属全髋假体置换术后可以产生大量的钴铬金属离子而使机体内血液尿液中金属离子水平升高,而金属离子水平升高后可能会对机体产生不利影响,本文就金属对金属全髋假体置换术后对机体的影响作一综述。     

Probing determinants of the metal ion selectivity in carbonic anhydrase using mutagenesis

Few studies measuring thermodynamic metal ion selectivity of metalloproteins have been performed, and the major determinants of metal ion selectivity in proteins are not yet well understood. Several features of metal ion binding sites and metal coordination have been hypothesized to alter the transition metal selectivity of chelators, including (1) the polarizability of the coordinating atom, (2) the relative sizes of the binding site and the metal ion, and (3) the metal ion binding site geometry. To test these hypotheses, we have measured the metal ion affinity and selectivity of a prototypical zinc enzyme, human carbonic anhydrase II (CAII), and a number of active site variants where one of the coordinating ligands is substituted by another side chain capable of coordinating metal. CAII and almost all of the variants follow the inherent metal ion affinity trend suggested by the Irving-Williams series, demonstrating that this trend operates within proteins as well as within small molecule chelators and may be a dominant factor in metal ion selectivity in biology. Neither the polarizability of the liganding side chains nor the size of the metal ion binding site correlates strongly with metal ion specificity; instead, changes in metal ion specificity in the variants correlate with the preferred coordination number and geometry of the metal ion. This correlation suggests that a primary feature driving deviations from the inherent ligand affinity trend is the positioning of active site groups such that a given metal ion can adopt a preferred coordination number/geometry.     

Modelling Bioaccumulation and Toxicity of Metal Mixtures

Bioaccumulation of metals in mixtures may demonstrate competitive, anticompetitive, or non-competitive inhibition, as well as various combinations of these and/or enhancement of metal uptake. These can be distinguished by plotting (metal in water)/(metal in tissue) against metal in water and comparison to equivalent plots for single-metal exposure. For the special case of pure competitive inhibition where only one site of uptake is involved, inhibition of metal accumulation in any metal mixture can be predicted from bioaccumulation of the metals when present singly. This is consistent with the commonly used Biotic Ligand Model (BLM) but does not explain bioaccumulation of metals in Hyalella azteca. Options for modelling toxicity of metal mixtures include concentration or response addition based on metal concentrations in either water or tissues. If the site of toxic action is on the surface of the organism, if this is the same as the site of metal interaction for bioaccumulation, if there is only one such type of site, and if metal bioaccumulation interactions are purely competitive (as in the BLM), then metal toxicity should be concentration additive and predictable from metal concentrations in either water or tissues. This is the simplest toxicity interaction to model but represents only one of many possibilities. The BLM should, therefore, be used with caution when attempting to model metal interactions, and other possibilities must also be considered.     

Trace metal speciation in a wastewater wetland and its bioaccumulation in tilapia Oreochromis niloticus

Trace metal species in the water column of a canal system forming a wetland filled with wastewater were analyzed to determine their correlation with metal accumulation in the gills of locally fished Oreochromis niloticus. The metal concentrations in the suspended particles and water dissolved were analyzed. The metal species were calculated using Windermere Humic Aqueous Model version VII showing that the high organic matter and major cation contents were important parameters. Also, the free ion metal concentration was expected to correlate with the organic matter aromaticity; however, organic compounds other than humic susbtances seem to be complexing the metals in the system. Additionally, no clear correlation could be found between metal accumulation in gills and any of the dissolved metal species. Nonetheless, certain trends could be seen between the calculated metal species and metal accumulation in the tilapia from the suspended particles.     

Metal ion resistance in fungi: molecular mechanisms and their regulated expression

One stress response in cells is the ability to survive in an environment containing excessive concentrations of metal ions. This paper reviews current knowledge about cellular and molecular mechanisms involved in the response and adaptation of various fungal species to metal stress. Most cells contain a repertoire of mechanisms to maintain metal homeostasis and prevent metal toxicity. Roles played by glutathione, related (gamma-EC)nG peptides, metallothionein-like polypeptides, and sulfide ions are discussed. In response to cellular metal stress, the biosynthesis of some of these molecules are metalloregulated via intracellular metal sensors. The identify of the metal sensors and the role of metal ions in the regulation of biosynthesis of metallothionein and (gamma-EC)nG peptides are subjects of much current attention and are discussed herein.     

高等植物重金属耐性与超积累特性及其分子机理研究

由于重金属污染日益严重, 重金属在土壤_植物系统中的行为引起了人们的高度重视。高等植物对重金 属的耐性与积累性, 已经成为污染生态学研究的热点。近年来, 由于分子生态学等学科的发展, 有关植物对重金属的解毒和耐性机理、重金属离子富集机制的研究取得了较大进展。高等植物对重金属的耐性和积累在种间和基因型之间存在很大差异。根系是重金 属等土壤污染物进入植物的门户。根系分泌物改变重金属的生物有效性和毒性, 并在植物吸收重金属的过程中发挥重要作用。土壤中的大部分重金属离子都是通过金属转运蛋白进入根细胞, 并在植物体内进一步转运至液泡贮存。在重金属胁迫条件下植物螯合肽 (PC) 的合成是植物对胁迫的一种适应性反应。耐性基因型合成较多的PC, 谷胱甘肽 (GSH) 是合成PC的前体, 重金属与PC螯合并转移至液泡中贮存, 从而达到解毒效果。金属硫蛋白 (MTs) 与PC一样, 可以与重金属离子螯合, 从而降低重金属离子的毒性。该文从分子水平上论述了根系分泌物、金属转运蛋白、MTs、PC、GSH在重金属耐性及超积累性中的作用, 评述了近 10年来这方面的研究进展, 并在此基础上提出存在的问题和今后研究的重点。     

Use ofCladophora glomerata to monitor heavy metals in rivers

Methods were developed for the use ofCladophora glomerata to monitor heavy metal concentrations in flowing waters. At least under conditions without marked fluctuations in ambient metal concentration, there was no detectable difference in the metal concentrations of young plants between terminal 2-cm lengths of filament and whole plants. In order to establish the relationship between metal concentration in plant and that in water, 60 algal and water samples were analyzed from sites in northern England for Fe, Cu, Zn, Cd and Pb. Other environmental variables were measured at the time in order to assess their influence on metal accumulation. There were highly significant correlations for each of the five metals between concentrations in alga and water. The regression equations relating metal in alga to metal in water permit an unknown environmental metal concentration to be estimated from the algal concentration. Multiple stepwise regression analyses were used to indicate environmental factors which may influence metal accumulation; for instance, Fe appears to have a positive influence on Cu accumulation. In generalCladophora accumulates much less metal than bryophytes, but the slope relating metal in alga to metal in water is steeper, particularly for Pb. This means thatCladophora is especially useful where there is a need for a sensitive indicator of differences between sites or sampling occasions.     

Use of Algae for Removing Heavy Metal Ions From Wastewater: Progress and Prospects

ABSTRACT

Many algae have immense capability to sorb metals, and there is considerable potential for using them to treat wastewaters. Metal sorption involves binding on the cell surface and to intracellular ligands. The adsorbed metal is several times greater than intracellular metal. Carboxyl group is most important for metal binding. Concentration of metal and biomass in solution, pH, temperature, cations, anions and metabolic stage of the organism affect metal sorption. Algae can effectively remove metals from multi-metal solutions. Dead cells sorb more metal than live cells. Various pretreatments enhance metal sorption capacity of algae. CaCl₂ pretreatment is the most suitable and economic method for activation of algal biomass. Algal periphyton has great potential for removing metals from wastewaters. An immobilized or granulated biomass-filled column can be used for several sorption/desorption cycles with unaltered or slightly decreased metal removal. Langmuir and Freundlich models, commonly used for fitting sorption data, cannot precisely describe metal sorption since they ignore the effect of pH, biomass concentration, etc. For commercial application of algal technology for metal removal from wastewaters, emphasis should be given to: (i) selection of strains with high metal sorption capacity, (ii) adequate understanding of sorption mechanisms, (iii) development of low-cost methods for cell immobilization, (iv) development of better models for predicting metal sorption, (v) genetic manipulation of algae for increased number of surface groups or over expression of metal binding proteins, and (vi) economic feasibility.     

Chloroplastic and mitochondrial metal homeostasis

Transition metal deficiency has a strong impact on the growth and survival of an organism. Indeed, transition metals, such as iron, copper, manganese and zinc, constitute essential cofactors for many key cellular functions. Both photosynthesis and respiration rely on metal cofactor-mediated electron transport chains. Chloroplasts and mitochondria are, therefore, organelles with high metal ion demand and represent essential components of the metal homeostasis network in photosynthetic cells. In this review, we describe the metal requirements of chloroplasts and mitochondria, the acclimation of their functions to metal deficiency and recent advances in our understanding of their contributions to cellular metal homeostasis, the control of the cellular redox status and the synthesis of metal cofactors.     

THE INFLUENCE OF SIZE ON THE ACCUMULATED AMOUNTS OF METALS (Cu, Pb, Cd, Zn AND Ca) IN SIX SPECIES OF SLUG SAMPLED FROM A CONTAMINATED WOODLAND SITE

Heavy metal concentrations in 6 terrestrial slug species (Derocerasreticulatum, D. caruanae, Arionater, A. hortensis, A. subfuscusand Milax budapestensis) inhabiting a disused Pb/Zn mine sitewere measured by atomic absorption spectrophotometry. Relationshipsbetween dry weight: metal content and dry weight: metal concentration,respectively, were investigated by regression analysis beforeand after log transformation. Interspecies, as well as inter-metal differences in metal accumulationwere more effectively demonstrated by comparing metal content:dry body weight relationships, as opposed to metal concentration:dry body weight relationships. Regression analysis revealed differences in metal accumulationbetween the non-essential trace metals Pb/Cd and the metabolicallyessential trace metals Zn/Cu. Species differences in metal accumulation were more pronouncedwhen their coefficients of functional regression were compared,the greatest differences being observed for species belongingto different genera. However, the presence of a high level ofintrinsic variability in metal levels reduces the effectivenessand significance of the metal content: dry body weight expressions,and also detracts from the immediate prospect of using terrestrialslugs as biomonitors of environmental metal pollution. (Received 10 March 1989; accepted 25 November 1989)     

Photothermal Enhancement in Core-Shell Structured Plasmonic Nanoparticles

Plasmonic nanoparticles (NPs) with photothermal effects can be exploited as efficient heat sources in various applications. Here, the photothermal properties in core-shell structured plasmonic NPs, including metal/silica NP, silica/metal NP, and metal/silica/metal NP, are investigated. Compared with bare metal NPs, the core-shell plasmonic NPs not only exhibit extremely agile tunability in the surface plasmon resonances but also show considerably enhanced photothermal effects in terms of the maximum temperature rise. For metal/silica NPs and metal/silica/metal NPs, the SiO₂ shells function as effective thermal-protective layers for enhanced photothermal effect. For silica/metal NPs, the SiO₂ core and the metal shell show uniform temperature rise. These findings are essential for applying the core-shell structured plasmonic NPs on photothermal imaging, nanofluidics, etc.     

Chromium and cadmium removal from wastewater using duckweed - Lemna gibba L. and ultrastructural deformation due to metal toxicity

Phytoremediation potential of Lemna gibba was evaluated for chromium (Cr) and cadmium (Cd) under laboratory conditions for variable metal load of 1?mg/l, 3?mg/l, 5mgl, 7?mg/l and 9?mg/l, respectively, for 7 and 15?days of treatment period. Effects of both metals on structural attributes of L. gibba were also analyzed by Scanning Electron Microscopic (SEM) study. The metal removal percentage by L. gibba for Cr metal was found in the range of 37.3% to 98.6% and for cadmium it was found within the range of 81.6% to 94.6%. Bio concentration factor (BCF) of L .gibba was observed within the range of 37 to 295 for Cr metal and for Cd metal it ranged from 237 to 1144, which shows that the plant is a hyper accumulator for Cd metal and moderate accumulator for Cr metal. Statistical analysis (Two-way ANOVA) was performed on experimental results to confirm the individual effect of metal concentration and treatment period as well as cumulative effect of both factors together on percentage metal removal and on BCF. Research studies indicated that with the progress of treatment period metal removal percentage increases but increasing metal load during experiment negatively co-relates the metal removal percentage and BCF.     

Uncoupling metallonuclease metal ion binding sites via nudge mutagenesis

The hydrolysis of phosphodiester bonds by nucleases is critical to nucleic acid processing. Many nucleases utilize metal ion cofactors, and for a number of these enzymes two active-site metal ions have been detected. Testing proposed mechanistic roles for individual bound metal ions has been hampered by the similarity between the sites and cooperative behavior. In the homodimeric PvuII restriction endonuclease, the metal ion dependence of DNA binding is sigmoidal and consistent with two classes of coupled metal ion binding sites. We reasoned that a conservative active-site mutation would perturb the ligand field sufficiently to observe the titration of individual metal ion binding sites without significantly disturbing enzyme function. Indeed, mutation of a Tyr residue 5.5 A from both metal ions in the enzyme-substrate crystal structure (Y94F) renders the metal ion dependence of DNA binding biphasic: two classes of metal ion binding sites become distinct in the presence of DNA. The perturbation in metal ion coordination is supported by 1H-15N heteronuclear single quantum coherence spectra of enzyme-Ca(II) and enzyme-Ca(II)-DNA complexes. Metal ion binding by free Y94F is basically unperturbed: through multiple experiments with different metal ions, the data are consistent with two alkaline earth metal ion binding sites per subunit of low millimolar affinity, behavior which is very similar to that of the wild type. The results presented here indicate a role for the hydroxyl group of Tyr94 in the coupling of metal ion binding sites in the presence of DNA. Its removal causes the affinities for the two metal ion binding sites to be resolved in the presence of substrate. Such tuning of metal ion affinities will be invaluable to efforts to ascertain the contributions of individual bound metal ions to metallonuclease function.     

Molecular design of the microbial cell surface toward the recovery of metal ions

The genetic engineering of microorganisms to adsorb metal ions is an attractive method to facilitate the environmental cleanup of metal pollution and to enrich the recovery of metal ions such as rare metal ions. For the recovery of metal ions by microorganisms, cell surface design is an effective strategy for the molecular breeding of bioadsorbents as an alternative to intracellular accumulation. The cell surface display of known metal-binding proteins/peptides and the molecular design of novel metal-binding proteins/peptides have been performed using a cell surface engineering approach. The adsorption of specific metal ions is the important challenge for the practical recovery of metal ions. In this paper, we discuss the recent progress in surface-engineered bioadsorbents for the recovery of metal ions.