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Divalent Metal Cations (divalent + metal_cation)
Selected AbstractsBiotic ligand model of the acute toxicity of metals.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2001Abstract The biotic ligand model (BLM) of acute metal toxicity to aquatic organisms is based on the idea that mortality occurs when the metal,biotic ligand complex reaches a critical concentration. For fish, the biotic ligand is either known or suspected to be the sodium or calcium channel proteins in the gill surface that regulate the ionic composition of the blood. For other organisms, it is hypothesized that a biotic ligand exists and that mortality can be modeled in a similar way. The biotic ligand interacts with the metal cations in solution. The amount of metal that binds is determined by a competition for metal ions between the biotic ligand and the other aqueous ligands, particularly dissolved organic matter (DOM), and the competition for the biotic ligand between the toxic metal ion and the other metal cations in solution, for example, calcium. The model is a generalization of the free ion activity model that relates toxicity to the concentration of the divalent metal cation. The difference is the presence of competitive binding at the biotic ligand, which models the protective effects of other metal cations, and the direct influence of pH. The model is implemented using the Windermere humic aqueous model (WHAM) model of metal,DOM complexation. It is applied to copper and silver using gill complexation constants reported by R. Playle and coworkers. Initial application is made to the fathead minnow data set reported by R. Erickson and a water effects ratio data set by J. Diamond. The use of the BLM for determining total maximum daily loadings (TMDLs) and for regional risk assessments is discussed within a probabilistic framework. At first glance, it appears that a large amount of data are required for a successful application. However, the use of lognormal probability distributions reduces the required data to a manageable amount. [source] Lipid,nucleic acids interactions as base for organization and expression of cellular genomeINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2010V. V. Kuvichkin Abstract Although lipid,nucleic acid interactions have been studied, with certain or little progress, for more than 30 years, it is only in recent years that the problem has received particular attention. It should, however, be noted that most studies deal with DNA-cationic surfactants interactions, whereas DNA-zwitterionic interactions, which are more complex and close to nature, are poorly investigated. The long-standing studies of the triple complexes: DNA,phosphatidylcholine liposomes,divalent metal cations allow us to confirm that these complexes are responsible for the formation of not only the structures existing in DNA,cationic liposome complexes but also some other cellular structures. The author proposed hypothesis about the involvement of direct DNA,lipid interactions in the nuclear pore assembly. Only taking into account interactions between DNA and lipids of cellular membrane, one can explain the origin of such structures as nucleoid, nuclear pore, and nuclear matrix. The formation of triple complexes was accompanied by the aggregation and partial fusion of liposomes as was shown by cryo-TEM technique. The author has presented new data on the structure of triple complexes, which were obtained by phase contrast cryo-TEM. Biophysical data on the liposomes fusion during triple complex formation and perspective of their computer simulation are also presented. DNA acts as a fusogen in this process and it unwinds in the region of liposomes fusion. The nuclear envelope and pore complexes assembly is provided by membrane vesicles fusion. Author has proposed that the DNA-induced fusion of zwitterionic liposomes in vitro may suggest the involvement of direct lipids,DNA interaction in nuclear envelope assembly. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Conformation-dependent intermolecular interaction energies of the triphosphate anion with divalent metal cations.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2004Application to the ATP-binding site of a binuclear bacterial enzyme. Abstract We have explored the conformation-dependent interaction energy of the triphosphate moiety, a key constituent of ATP and GTP, with a closed-shell divalent cation, Zn2+, used as a probe. This was done using the SIBFA polarizable molecular mechanics procedure. We have resorted to a previously developed approach in which triphosphate is built out from its elementary constitutive fragments, and the intramolecular, interfragment, interaction energies are computed simultaneously with their intermolecular interactions with the divalent cation. This approach has enabled reproduction of the values of the intermolecular interaction energies from ab initio quantum-chemistry with relative errors <3%. It was extended to the complex of a nonhydrolyzable analog of ATP with the active site of a bacterial enzyme having two Mg2+ cations as cofactors. We obtained following energy-minimization a very close overlap of the ATP analog over its position from X-ray crystallography. For models of the ATP analog,enzyme complex encompassing up to 169 atoms, the values of the SIBFA interaction energies were found to match their DFT counterparts with relative errors of <2%. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 160,168, 2004 [source] Effect of metal cations on the conformation and inactivation of recombinant human factor VIIIJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2004Tiffany S. Derrick Abstract Heavy metals have been implicated in the aggregation of proteins and the pathophysiology of several neurodegenerative diseases. Herein, we describe the interaction of recombinant human factor VIII (rhFVIII) with Al+3, Tb+3, Co+2, and Fe+3 using a combination of intrinsic fluorescence, circular dichroism, and high-resolution fourth-derivative absorbance analysis. rhFVIII in solution was titrated with the metal cations and the properties of the resulting complexes were examined. rhFVIII has a tendency to aggregate and inactivate slowly over time under physiological conditions, but this aggregation process is greatly accelerated in the presence of metals with Al+3 being the most efficient. This leads to a complete loss of activity of the protein. Al+3 -induced conformational changes in the protein were small but detectable with limited changes seen in secondary and tertiary structure. Because rhFVIII is a multidomain protein with subunits linked through divalent metal cations, the small intramolecular changes seen may be attributed to rearrangements of the subunits to an aggregation-competent conformer that is very similar to that of the native form. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2549,2557, 2004 [source] A new ferrous iron-uptake transporter, EfeU (YcdN), from Escherichia coliMOLECULAR MICROBIOLOGY, Issue 1 2006Cornelia Große Summary Escherichia coli possesses multiple routes for iron uptake. Here we present EfeU (YcdN), a novel iron acquisition system of E. coli strain Nissle 1917. Laboratory strains of E. coli such as K12 lack a functional (efeU) ycdN gene caused by a frameshift mutation. EfeU, a member of the oxidase-dependent iron transporters (OFeT), is a homologue of the iron permease Ftr1p from yeast. The ycdN gene is part of the ycdNOB tricistronic operon which is expressed in response to iron deprivation in a Fur-dependent manner. Expression of efeU resulted in improved growth of an E. coli mutant lacking all known iron-uptake systems and mediated increased iron uptake into cells. Furthermore, the presence of other divalent metal cations did not impair growth of strains expressing efeU. The EfeU protein functioned as ferrous iron permease in proteoliposomes in vitro. Topology analysis indicated that EfeU is an integral cytoplasmic membrane protein exhibiting seven transmembrane helices. Two REXXE motifs within transmembrane helices of OFeT family members are implicated in iron translocation. Site-directed mutagenesis of each REGLE motif of EfeU diminished iron uptake in vivo and growth yield. In vitro the EfeU variant protein with an altered first REGLE motif was impaired in iron permeation, whereas activity of the EfeU variant with a mutation in the second motif was similar to the wild-type protein. [source] | |||||||||||||