Articles de revues : « Bivalent metal cations »

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Yeung, I. Y. L., E. Phillips, D. A. Mann et C. H. Barton. « Oxidant regulation of the bivalent cation transporter Nramp1 ». Biochemical Society Transactions 32, n^o 6 (26 octobre 2004) : 1008–10. http://dx.doi.org/10.1042/bst0321008.

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Nramp1 (murine natural resistance-associated macrophage protein 1 gene)/Slc11a1 (solute carrier family 11 member a1 gene) encodes a bivalent-metal/iron transporter that is expressed within late endosomes/lysosomes of macrophages. A functionally null Nramp1 allele that exhibits impaired bivalent cation transport enables excessive growth of intracellular pathogens. Iron is important for many cellular activities, including defence against pathogens; however, redox-active/free iron can participate in Fenton chemistry that generates reactive oxygen species. Using Raw264.7 cells, non-functional for Nramp1, and stable Nramp1 transfectants, we have examined the effects of impaired bivalent cation transport on macrophage function using glutathione depletion as OS (oxidant stress). Our results demonstrate that OS itself is a signal for increasing Nramp1 transcription and that Nramp1 expression protects against OS. We suggest that OS-mediated protection by Nramp1 function may arise from direct removal of redox-active bivalent cations from a cytosolic pool. We show that OS transcriptional responses are probably mediated by the Sp1 transcription factor.

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Rowatt, E., et R. J. P. Williams. « The interaction of cations with the dye arsenazo III ». Biochemical Journal 259, n^o 1 (1 avril 1989) : 295–98. http://dx.doi.org/10.1042/bj2590295.

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1. The dye arsenazo III combines with a selection of cations to give an altered absorption spectrum. 2. Large metal cations such as Ca2+, La3+ and quadrivalent cations give a 1:1 complex with two new absorption peaks at about 610 nm and 655 nm and a KD of about 10(-6) M. 3. Aliphatic polyamines and complex cobalt ions give a 1:1 complex, with one absorption peak at about 610 nm and a KD from 10(-6) to 10(-3) M. 4. Small metal cations finally form a 2:1 complex and also have one absorption peak at about 610 nm, but with a KD of 10(-5)-10(-4) M. 5. The absorption peak at 610 nm is similar to that formed at high pH in the absence of bivalent cations and is due to ionization of phenolic groups with the dye molecule in an extended form. 6. The peak at 655 nm with 1:1 complex can be explained as a change in orientation of the diazo bonds caused by a conformational change of the molecule when it wraps around the single atom of Ca2+ or other large cation.

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GOSWAMI, Tapasree, Arin BHATTACHARJEE, Paul BABAL, Susan SEARLE, Elizabeth MOORE, Ming LI et Jenefer M. BLACKWELL. « Natural-resistance-associated macrophage protein 1 is an H+/bivalent cation antiporter ». Biochemical Journal 354, n^o 3 (8 mars 2001) : 511–19. http://dx.doi.org/10.1042/bj3540511.

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In mammals, natural-resistance-associated macrophage protein 1 (Nramp1) regulates macrophage activation and is associated with infectious and autoimmune diseases. Nramp2 is associated with anaemia. Both belong to a highly conserved eukaryote/prokaryote protein family. We used Xenopus oocytes to demonstrate that, like Nramp2, Nramp1 is a bivalent cation (Fe2+, Zn2+ and Mn2+) transporter. Strikingly, however, where Nramp2 is a symporter of H+ and metal ions, Nramp1 is a highly pH-dependent antiporter that fluxes metal ions in either direction against a proton gradient. At pH9.0, oocytes injected with cRNA from wild-type murine Nramp1 with a glycine residue at position 169 (Nramp1G169; P = 3.22×10-6) and human NRAMP1 (P = 3.87×10-5) showed significantly enhanced uptake of radiolabelled Zn2+ compared with water-injected controls. At pH5.5, Nramp1G169 (P = 1.34×10-13) and NRAMP1 (P = 1.09×10-6) oocytes showed significant efflux of Zn2+. Zn2+ transport was abolished when the proton gradient was dissipated using carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Using pre-acidified oocytes, currents of 130±57 nA were evoked by 100µM Zn2+ at pH7.5, and 139±47 nA by 100µM Fe2+ at pH7.0, in Nramp1G169 oocytes; currents of 254±49 nA and 242±26 nA were evoked, respectively, in NRAMP1 oocytes. Steady-state currents evoked by increasing concentrations of Zn2+ were saturable, with apparent affinity constants of approx. 614nM for Nramp1G169 and approx. 562nM for NRAMP1 oocytes, and a curvilinear voltage dependence of transporter activity (i.e. the data points approximate to a curve that approaches a linear asymptote). In the present study we propose a new model for metal ion homoeostasis in macrophages. Under normal physiological conditions, Nramp2, localized to early endosomal membranes, delivers extracellularly acquired bivalent cations into the cytosol. Nramp1, localized to late endosomal/lysosomal membranes, delivers bivalent cations from the cytosol into this acidic compartment where they may directly affect antimicrobial activity.

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AGRANOFF, Daniel, Lauren COLLINS, David KEHRES, Tom HARRISON, Michael MAGUIRE et Sanjeev KRISHNA. « The Nramp orthologue of Cryptococcus neoformans is a pH-dependent transporter of manganese, iron, cobalt and nickel ». Biochemical Journal 385, n^o 1 (14 décembre 2004) : 225–32. http://dx.doi.org/10.1042/bj20040836.

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Cryptococcus neoformans is an important human opportunistic pathogen and a facultative intracellular parasite, particularly in HIV-infected individuals. Little is known about metal ion transport in this organism. C. neoformans encodes a single member of the Nramp (natural resistance-associated macrophage protein) family of bivalent cation transporters, known as Cramp, which we have cloned and expressed in Xenopus laevis oocytes and Spodoptera frugiperda Sf 21 insect cells. Cramp induces saturable transport of a broad range of bivalent transition series cations, including Mn2+, Fe2+, Co2+ and Ni2+. Maximal cation transport occurs at pH 5.5–6.0, consistent with the proton gradient-based energetics of other Nramp orthologues. Mn2+ transport is diminished in the presence of 140 mM Na+, compatible with a Na+ slippage mechanism proposed for the Saccharomyces cerevisiae Nramp orthologue Smf1p. Cramp resembles Smf1p with respect to predicted membrane topology, substrate specificity and pH dependence, but differs in terms of its apparent affinity for Mn2+ and negligible inhibition by Zn2+. Cramp is the first Nramp orthologue from a fungal pathogen to be functionally characterized. Insights afforded by these findings will allow the formulation of new hypotheses regarding the role of metal ions in the pathophysiology of cryptococcosis.

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Lasia, Andrzej. « Study of the CEE mechanism by voltammetry and chronoamperometry ». Canadian Journal of Chemistry 64, n^o 12 (1 décembre 1986) : 2319–23. http://dx.doi.org/10.1139/v86-381.

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The electroreduction of bivalent metal cations may proceed by a CEE mechanism with a heterogenous chemical reaction on the electrode surface. The applications of the convolutive linear sweep voltammetry and chronoamperometry to study that mechanism are presented. The behaviour of the electrochemical reactions was simulated using an implicit finite difference technique for different values of kinetic parameters. The simulated curves were analysed and an agreement between the introduced and obtained data was found.

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Field, A. M., E. Rowatt et R. J. P. Williams. « The interaction of cations with lipopolysaccharide from Escherichia coli C as shown by measurement of binding constants and aggregation reactions ». Biochemical Journal 263, n^o 3 (1 novembre 1989) : 695–702. http://dx.doi.org/10.1042/bj2630695.

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Lipopolysaccharide from Escherichia coli C interacts with polyvalent cations at low ionic strength at more than one site. The first site has high affinity with a KD value of 10(-8) M for Ca2+ and even stronger binding for [(NH3)5CoNH2Co(NH3)5]5+ and La3+. The high-affinity site for the latter cations is beyond the sensitivity of the assay method. The second, low-affinity, site for bivalent cations has a Km of 10(-3) M, whereas, for tervalent and quinquevalent metal cations and spermine and hexacyclen (1,4,7,10,13,16-hexa-azacyclo-octadecane), this constant has a value of 10(-5) M. Binding of cations to the high-affinity site does not alter the aggregation state of the lipopolysaccharide, but combination with the low-affinity site gives particles twice the size of those of the sodium salt. Very high Ca2+ concentrations (30 mM) give particles eight times the size of those of the sodium salt.

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Bie?kowski, Tomasz, Agnieszka Brodzik-Bie?kowska et Witold Danikiewicz. « Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds ». Journal of Mass Spectrometry 37, n^o 6 (2002) : 617–22. http://dx.doi.org/10.1002/jms.322.

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Kar, L., P. Matsumura et M. E. Johnson. « Bivalent-metal binding to CheY protein. Effect on protein conformation ». Biochemical Journal 287, n^o 2 (15 octobre 1992) : 521–31. http://dx.doi.org/10.1042/bj2870521.

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CheY is a 14 kDa cytoplasmic protein that is activated by the transfer of a phosphoryl moiety to Asp-57 from phosphoCheA during signal transduction in bacterial chemotaxis. It has been established that metal ions are necessary for the autophosphorylation of CheA, the transfer of phosphate from phosphoCheA to CheY and the autodephosphorylation of phosphoCheY. In this work, paramagnetic relaxation enhancement has been used in conjunction with one- and two-dimensional n.m.r. to study the interaction of CheY with bivalent metal ions. These studies have led to the discovery of two conformations of the protein in water, corresponding to the metal-free and the metal-bound states. Binding of bivalent cations like Mg2+, Ca2+, Sr2+, Zn2+ and Mn2+ results in a conformational change from the metal-free to the metal-bound state. Preliminary assignments of the aromatic proton resonances are reported. Comparison of phase-sensitive double-quantum-filtered COSY, homonuclear Hartmann-Hahn coherence transfer and nuclear Overhauser enhancement spectra from the metal-bound and metal-free protein indicates that Trp-58, Thr-87 and Tyr-106 are particularly affected by the conformational change involved, and that this change is limited to a small number of residues. In addition, homonuclear Hartmann-Hahn coherence transfer experiments with paramagnetic Mn2+ show significant suppression of cross-peaks associated with Trp-58 and several neighbouring residues. Comparison of the distances estimated using n.m.r. with the CheY crystal structure indicates that the n.m.r. results are consistent with bivalent metal binding at the cluster of aspartic acid residues that includes Asp-13 and Asp-57. These studies also demonstrate the utility of paramagnetic metal-induced relaxation in conjunction with two-dimensional n.m.r. measurements for exploring ligand-binding sites.

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Veiga, Nicolás, Julia Torres, Carla Bazzicalupi, Antonio Bianchi et Carlos Kremer. « The copper(ii)–phytate–terpyridine ternary system : the first crystal structures showing the interaction of phytate with bivalent metal and ammonium cations ». Chem. Commun. 50, n^o 95 (2014) : 14971–74. http://dx.doi.org/10.1039/c4cc07226j.

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This work reports the solution and crystallographic study of the Cu(ii)–phytate–terpyridine systems, showing for the first time the phytate binding mode toward a bivalent cation and protonated polyamine groups.

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Plazinski, Wojciech, et Mateusz Drach. « Binding of bivalent metal cations by α-l-guluronate : insights from the DFT-MD simulations ». New Journal of Chemistry 39, n^o 5 (2015) : 3987–94. http://dx.doi.org/10.1039/c4nj02206h.

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Dmitrieva, E. S., E. E. Pankratova, Tatiana S. Anokhina, V. V. Vinokurov et Alexey V. Volkov. « Crosslinked Sodium Alginate as a Material for Nanolfiltration Protonic and Aprotonic Solvents ». Key Engineering Materials 899 (8 septembre 2021) : 745–51. http://dx.doi.org/10.4028/www.scientific.net/kem.899.745.

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In this work, for the first time, salts of bivalent and trivalent metals were used as crosslinking agents for nanofiltration membranes based on sodium alginate. The developed membranes were investigated for chemical stability in protic and aprotic solvents, the dependence of the permeability of these solvents on their sorption into the membrane material was obtained. The separating properties of membranes based on sodium alginate crosslinked with metal cations were investigated. The retention coefficient of the model substance with a molecular weight of 626 g/mol, dissolved in ethanol, was 97%.

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Gun’ko, Vladimir, Lyudmyla Andriyko, Vladimir Zarko, Andrij Marynin, Valentyn Olishevskyi et Wladyslaw Janusz. « Effects of dissolved metal chlorides on the behavior of silica nanoparticles in aqueous media ». Open Chemistry 12, n^o 4 (1 avril 2014) : 480–91. http://dx.doi.org/10.2478/s11532-013-0386-1.

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AbstractEffects of chlorides of univalent (LiCl, NaCl, KCl), bivalent (MgCl2, BaCl2) and trivalent (AlCl3) metals at different concentration (0.001–0.1 M) on the behavior of nanosilica A-200 (0.5–5 wt.%) in aqueous media are analyzed using photon correlation spectroscopy (particle size distribution, PSD), electrophoresis (zeta potential ζ), potentiometric titration (surface charge density), and estimation of screening length of primary particles and their aggregates. The zeta potential and the PSD are affected by silica content, pH, and concentration and type of dissolved salts. Smaller but more strongly hydrated Li+ cations caused stronger nonlinear dependences of the zeta potential on pH and salt content than Na+ or K+. This nonlinearity is much stronger at a lower content of silica (0.5–1 wt.%) than at C A-200 = 2.5 or 5 wt.%. At a high concentration of nanosilica (5 wt.%) the effect of K+ ions causes stronger diminution of the negative value of the zeta potential due to better adsorption of larger cations. Therefore, the influence of K+ on increasing screening length is stronger than that of Na+ for both primary nanoparticles and their aggregates. A similar difference in the ζ values is observed for different in size cations Ba2+ and Mg2+.

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Oueslati, W., M. Meftah, H. Ben Rhaiem et A. Ben Haj Amara. « Selectivity of Na-Montmorillonite versus Concentration of Two Competitive Bivalent Cations (, ) : Quantitative XRD Investigation ». Advances in Materials Science and Engineering 2009 (2009) : 1–4. http://dx.doi.org/10.1155/2009/385673.

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The goal of this paper is to examine, by quantitative XRD analysis, the effect of heavy metal cation concentrations (, ) on the selectivity phenomenon in the case of dioctahedral smectite (i.e., Na-montmorillonite). The quantitative XRD analysis is achieved using an indirect method based on the comparison of experimental XRD profiles to those calculated using structural models. The obtained results show that for strong metals concentrations (i.e., N), the host material presents heterogeneous structure characterized by interstratified hydration states between 1 W and 2 W (i.e., respectively, one and two water layer hydration state) attributed to cation. For low concentration, the values investigation indicates that montmorillonite remains saturated with characterized by homogeneous 1 W hydration state.

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Maeda, Hiroshi, Tsuyoshi Hiramatsu et Shoichi Ikeda. « Effects of Bivalent Metal Cations on the Conformation and Aggregation of Poly(L-glutamic acid) ». Bulletin of the Chemical Society of Japan 59, n^o 2 (février 1986) : 587–91. http://dx.doi.org/10.1246/bcsj.59.587.

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Ammar, Marwa, Walid Oueslati, Hafsia Ben Rhaiem et Abdesslem Ben Haj Amara. « XRD profile modeling approach tools to investigate the effect of charge location on hydration behavior in the case of metal exchanged smectite ». Powder Diffraction 28, S2 (septembre 2013) : S284—S300. http://dx.doi.org/10.1017/s0885715613000973.

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This work aims to investigate the hydration behavior and structural properties of two dioctahedral smectites with contrasting location charge (beidellite SbId-1 and montmorillonite SWy-2) according to the nature of the bivalent compensator heavy metal cations (i.e. Hg (II), Ni (II), Ba (II) and Mg (II)). This study is achieved using XRD profile modeling approach based on the simulation of the 00l reflection which allowed us to determine structural characteristics along the c* axis related to the nature, abundance, size, position and organization of exchangeable cation and water molecule in the interlamellar space along the c* axis. The obtained results show that a heterogeneous hydration behavior is systematically observed in all studied samples and the structural models, used to fit samples with tetrahedral charge, are more heterogeneous than smectite with an octahedral sheets substitution. In the case of exchanged beidellite specimen, the proposed models are described by a mixed layer structure with variable abundance containing respectively, dehydrated (0W), mono-hydrated (1W) and bihydrated (2W) layers. Whereas, in the case of the montmorillonite, the absence of 0W hydration state is noted.

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Dashkhuu Khasbaatar, A., Young Gun Ko et Ung Su Choi. « Adsorption and equilibrium adsorption modeling of bivalent metal cations on viscose rayon succinate at different pHs ». Reactive and Functional Polymers 67, n^o 4 (avril 2007) : 312–21. http://dx.doi.org/10.1016/j.reactfunctpolym.2007.01.003.

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Coolbear, T., J. M. Whittaker et R. M. Daniel. « The effect of metal ions on the activity and thermostability of the extracellular proteinase from a thermophilic Bacillus, strain EA.1 ». Biochemical Journal 287, n^o 2 (15 octobre 1992) : 367–74. http://dx.doi.org/10.1042/bj2870367.

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The proteinase from the extremely thermophilic Bacillus strain EA.1 exhibits maximum stability at a pH of approx. 6.5. In the presence of calcium ions the half-life at 95 degrees C of the enzyme at this pH was 17 min, and loss of activity followed first-order decay kinetics. The role of metal ions in the activity and stability of the enzyme was studied using the holoenzyme, the metal-depleted apoenzyme, and a zinc-enriched apoenzyme preparation. Zinc and calcium ions were the preferred bivalent cations for the active site and stabilization site(s) respectively. Stabilization by metal ions was not in itself a highly stringent process, but ions other than calcium which stabilized the enzyme generally had a concomitant inhibitory effect on activity. Inhibition and stabilization of the enzyme by cations were concentration-dependent effects and certain ions activated the apoenzyme but not the holoenzyme. Manganese(II) ions conferred some stability and also activated the enzyme, but in the latter case were not as effective as zinc ions. The results are discussed with reference to the ionic radii, co-ordination number and preferred ligand donors of the ions. Mercury(II) ions severely compromised enzyme activity and stability, and the effects of thiol-reactive agents suggest that thiol groups also have a role in enzyme integrity.

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SHIOKAWA, Daisuke, Harumi OHYAMA, Takeshi YAMADA et Sei-ichi TANUMA. « Purification and properties of DNase γ from apoptotic rat thymocytes ». Biochemical Journal 326, n^o 3 (15 septembre 1997) : 675–81. http://dx.doi.org/10.1042/bj3260675.

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We previously identified three distinct DNA endonucleases, DNases α, β and γ, present in rat thymocyte nuclei. On the basis of their enzymic and biochemical properties, γ-type DNase was regarded as a candidate for the apoptotic endonuclease. Here we purified DNase γ to apparent homogeneity from apoptotic rat thymocyte nuclei induced by X-irradiation and characterized its properties in detail. The purified DNase γ exhibited one predominant protein band on SDS/PAGE and an endonuclease activity in a zymography with an estimated molecular mass of 33 kDa. The molecular mass of the native form determined by G2000SW gel-filtration HPLC was 30 kDa. Amino acid analysis showed that the amino acid composition of DNase γ was similar to that of rat DNase I (molecular mass 32 kDa) but different with regard to alanine and lysine residues. The N-terminal amino acid sequence of DNase γ was revealed to be not identical with that of rat DNase I. In accordance with previous studies, homogeneously purified DNase γ requires both Ca2+ and Mg2+ for activity. This requirement could be partially supplied by Mn2+. Of the bivalent metal ions tested, Co2+, Ni2+, Cu2+ and Zn2+ inhibited DNase γ activity. These bivalent cations also suppressed apoptotic DNA fragmentation in rat thymocytes irradiated by X-rays. The same order of inhibitory ability was observed for these bivalent metal ions in vivo(in intact cells) and in vitro, suggesting that the suppression of apoptotic DNA fragmentation at the cellular level is due to the inhibition of DNase γ. DNase γ activity was found to exist at high levels in spleen, lymph node, thymus, liver and kidney, but little was present in brain, heart or pancreas. On the basis of these findings, together with previous data, we conclude that DNase γ is a novel DNase I-like endonuclease responsible for internucleosomal cleavage of chromatin during thymic apoptosis.

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Frutos, Alejandro A., Luis F. Sala, Graciela M. Escandar, Juan Manuel Salas Peregrin et Manuel Gonzalez Sierra. « Complex formation between D-lactobionate and bivalent metal ions. Studies in solution and in the solid state ». Canadian Journal of Chemistry 75, n^o 4 (1 avril 1997) : 405–13. http://dx.doi.org/10.1139/v97-046.

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The equilibrium reactions between deprotonated D-lactobionic acid (4-O-β-D-galactopyranosyl-D-gluconic acid) and cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and mercury(II) have been studied by potentiometric and spectrophotometric methods in aqueous solution. All measurements have been carried out at a temperature of 20.0 ± 0.1 °C and at an ionic strength of 0.100 M (NaNO3) with the corresponding stability constants calculated by applying computational methods. The interactions between the proposed cations with deprotonated D-lactobionic acid were compared with those corresponding to D-gluconic acid. Compounds of type: Co(C12H21O12)2•2H2O•C2H5OH, Ni(C12H21O12)2•2H2O•C2H5OH, Cu(C12H21O12)2•2H2O•C2H5OH, Zn(C12H21O12)2•2H2O•C2H5OH, and Cd(C12H21O12)2•2H2O•0.5C2H5OH have been isolated. These metal–sugar salts were characterized by elemental, thermogravimetric, and susceptibility analyses and FT-IR, UV–visible absorption, diffuse reflectance, and 13C NMR spectroscopies. Keywords: D-lactobionate, metal complexes, equilibrium constants, potentiometry, solid state studies.

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De Tommaso, Gaetano, Maria Michela Salvatore, Rosario Nicoletti, Marina DellaGreca, Francesco Vinale, Assunta Bottiglieri, Alessia Staropoli et al. « Bivalent Metal-Chelating Properties of Harzianic Acid Produced by Trichoderma pleuroticola Associated to the Gastropod Melarhaphe neritoides ». Molecules 25, n^o 9 (4 mai 2020) : 2147. http://dx.doi.org/10.3390/molecules25092147.

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Harzianic acid is a secondary metabolite of Trichoderma, structurally belonging to the dienyltetramic acid subgroup of the tetramic acids. Biological activities of harzianic acid are of great interest for its antimicrobial and plant growth-promoting activities, which might be related to its chelating properties. In the present work harzianic acid, isolated from cultures of a strain of Trichoderma pleuroticola associated to the gastropod Melarhaphe neritoides, was studied as a complexant agent of a number of biologically relevant transition metals (i.e., Zn2+, Fe2+, Cu2+, and Mn2+), using UV-VIS, potentiometry, MS and NMR techniques. Our findings show the coordination capacity of harzianic acid toward the above cations through the formation of neutral or charged complexes in a variable ratio depending on the metal and pH conditions.

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SUGA, Takayuki, Shunsuke IZUMI et Yoshikazu HIRAGA. « Biosynthesis of cyclic monoterpenoids - The role of bivalent metal cations in the cyclization of acyclic allylic diphosphates. » NIPPON KAGAKU KAISHI, n^o 4 (1988) : 629–34. http://dx.doi.org/10.1246/nikkashi.1988.629.

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Bruni, P., M. Pisani, A. Amici, C. Marchini, M. Montani et O. Francescangeli. « Self-assembled ternary complexes of neutral liposomes, deoxyribonucleic acid, and bivalent metal cations. Promising vectors for gene transfer ? » Applied Physics Letters 88, n^o 7 (13 février 2006) : 073901. http://dx.doi.org/10.1063/1.2173717.

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Soulière, Marie F., Jean-Pierre Perreault et Martin Bisaillon. « Characterization of the vaccinia virus D10 decapping enzyme provides evidence for a two-metal-ion mechanism ». Biochemical Journal 420, n^o 1 (28 avril 2009) : 27–35. http://dx.doi.org/10.1042/bj20082296.

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Decapping enzymes are required for the removal of the 5′-end cap of mRNAs. These enzymes exhibit a specific hydrolase activity, resulting in cleavage between the α- and β-phosphates of the m7GpppN cap to generate both m7GDP and monophosphorylated RNA products. Decapping enzymes have been found in humans, plants and yeasts, and have been discovered more recently in vaccinia virus (D10 protein). Although experimental evidences are lacking, three-metal- and two-metal-ion mechanisms have been proposed so far for the decapping enzymes. In the present study, we performed a biochemical characterization of the interaction of bivalent cations with the vaccinia virus D10 protein. Synergistic activation of the enzyme was observed in the presence of Mg2+ and Mn2+ ions, suggesting the existence of two metal-ion-binding sites on the D10 protein. Moreover, dual-ligand titration experiments using fluorescence spectroscopy demonstrated the presence of two metal-ion-binding sites on the enzyme. A three-dimensional structural model of the active site of the enzyme was generated which highlighted the importance of three glutamate residues involved in the co-ordination of two metal ions and a water molecule. Mutational analyses confirmed the role of two glutamate residues for the binding of metal ions. We demonstrate that one metal ion is co-ordinated by Glu132, while the second metal ion is co-ordinated by Glu145. Taken together, these results support the proposed two-metal-ion mechanistic model for the D10 decapping enzyme.

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Cigala, Rosalia Maria, Francesco Crea, Concetta De Stefano, Anna Irto et Silvio Sammartano. « Nature as Resource. Thermodynamic characterization of natural and synthetic polymers and their sequestering ability towards some bivalent metal cations ». Journal of Chemical Thermodynamics 150 (novembre 2020) : 106205. http://dx.doi.org/10.1016/j.jct.2020.106205.

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FENG, LIN, Yan Dan Dan, Chen Ya Wen, Fletcher Emmanuella E, Shi Hai Feng, Han Bang Xing et Zhou Yang. « Cloning, purification and enzymatic characterization of recombinant human Superoxide dismutase 1 expressed in Escherichia coli ». Acta Biochimica Polonica 65, n^o 2 (8 juillet 2018) : 235–40. http://dx.doi.org/10.18388/abp.2017_2350.

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Superoxide dismutase 1 (SOD1) is a metalloenzyme that catalyzes disproportion-action superoxide into molecular oxygen and hydrogen peroxide. In this study, the human SOD1 (hSOD1) gene was cloned, expressed, and purified. The hSOD1 gene was amplified from a pool of Bxpc3 cell cDNAs by PCR and cloned into expression vector pET-28a (+). The recombinant soluble hSOD1 was expressed in E.coli BL21 (DE3) at 37°C and purified by Nickel column affinity chromatography. The soluble hSOD1 was produced with a yield of 5.9 ug/mL medium. Considering that metal ions have a certain influence on the structure and activity of protein, we researched the influences of different concentrations of Cu2+ and Zn2+ on hSOD1 activity at induction and the time of activity detection. The results implied Cu2+ and Zn2+ can’t enhance SOD1 expression, however can improve the catalytic activity at induction. Furthermore, most of bivalent cations have an improve effect on enzyme activity at the time of detection.

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Kubrak, Olha I., Janet M. Storey, Kenneth B. Storey et Volodymyr I. Lushchak. « Production and properties of α-amylase fromBacillussp. BKL20 ». Canadian Journal of Microbiology 56, n^o 4 (avril 2010) : 279–88. http://dx.doi.org/10.1139/w10-014.

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As a result of screening Bacillus sp. strains isolated from different natural substrates, strain BKL20 was identified as a producer of a thermostable alkaline α-amylase. Maximum production of this α-amylase was achieved by optimizing culture conditions. Production of α-amylase seemed to be independent of the presence of starch in the culture medium and was stimulated by the presence of peptone (0.3%, m/v) and yeast extract (0.2%, m/v). The enzyme was thermostable and retained amylolytic activity after 30 min of incubation at 60 and 70 °C. High activity was maintained over a broad pH range, from 6.0 to 11.0, and the enzyme remained active after alkaline incubation for 24 h. Bacillus sp. BKL20 α-amylase was not stimulated by Ca2+or other bivalent metal cations and was not inhibited by EGTA or EDTA at 1–10 mmol/L, suggesting that this α-amylase is a Ca2+-independent enzyme. It also showed good resistance to both oxidizing (H2O2) and denaturating (urea) agents.

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Manavalan, Tamilvendan, Arulmani Manavalan, Shiyamsundar Ramachandran et Klaus Heese. « Identification of a Novel Thermostable Alkaline Protease from Bacillus megaterium-TK1 for the Detergent and Leather Industry ». Biology 9, n^o 12 (16 décembre 2020) : 472. http://dx.doi.org/10.3390/biology9120472.

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An increased need by the green industry for enzymes that can be exploited for eco-friendly industrial applications led us to isolate and identify a unique protease obtained from a proteolytic Bacillus megaterium-TK1 strain from a seawater source. The extracellular thermostable serine protease was processed by multiple chromatography steps. The isolated protease displayed a relative molecular weight (MW) of 33 kDa (confirmed by zymography), optimal enzyme performance at pH 8.0, and maximum enzyme performance at 70 °C with 100% substrate specificity towards casein. The proteolytic action was blocked by phenylmethylsulfonyl fluoride (PMSF), a serine hydrolase inactivator. Protease performance was augmented by several bivalent metal cations. The protease tolerance was studied under stringent conditions with different industrial dispersants and found to be stable with Surf Excel, Tide, or Rin detergents. Moreover, this protease could clean blood-stained fabrics and showed dehairing activity for cow skin with significantly reduced pollution loads. Our results suggest that this serine protease is a promising additive for various eco-friendly usages in both the detergent and leather industries.

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Xiao, Haiwen, Shengli Zhang, Jun Zhai, Qiang He, Adriaan Mels, Kejia Ning et Jie Liu. « Retention and distribution of Cu, Pb, Cr, and Zn in a full-scale hybrid constructed wetland receiving municipal sewage ». Water Science and Technology 67, n^o 10 (1 mai 2013) : 2257–64. http://dx.doi.org/10.2166/wst.2013.121.

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This study was conducted to investigate the retention and distribution of Cu, Pb, Cr, and Zn in a hybrid constructed wetland (CW) that consists of both vertical baffled flow wetlands (VBFWs) and horizontal subsurface flow wetlands (HSSFs) with unique flow regimes and oxygen distribution. The heavy metal concentrations in water, sediments, and plant tissues in the hybrid CW were analysed. The removal of heavy metals from the water stream in the monitoring period was not statistically significant. Metal concentrations in the sediments generally decreased along the wastewater treatment process. The reductive anaerobic condition in the VBFW may promote the sulphate reduction and form highly insoluble Cu, Pb, and Zn sulphides, resulting in the higher concentration of the bivalent cations in the VBFW sediments than the corresponding values in the HSSF; however, the aerobic and anoxic environments in the HSSF enhanced the removal of Cr with the co-precipitation of iron and manganese oxides, and their hydroxides. Metal concentrations in plant tissues were not significantly influenced by the concentrations in sediments, while roots contained statistically higher metal concentrations than stems and leaves. The sediments stored 94.01, 86.31, 95.85, and 89.51% of the total Cu, Pb, Cr, and Zn retained in the hybrid CW system, respectively, while only small fractions (<10%) were accumulated in the harvestable macrophyte tissues. It is important to clean not only the accessible sediments in free water surface tank and ponds but also the embedded sediments in vegetated beds for the sustainable removal of heavy metals.

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Pisani, Michela, Giovanna Mobbili, Milvia Marini, Oriano Francescangeli, Valerio Mori et Paolo Bruni. « An X-ray diffraction study of complexes of DNA and lactosyl-functionalised liposomes induced by bivalent metal cations : coexistence of different symmetries ». Liquid Crystals 40, n^o 2 (16 octobre 2012) : 137–48. http://dx.doi.org/10.1080/02678292.2012.735704.

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Schlattl, Maria, Marzell Buffler et Wilhelm Windisch. « Clay Minerals Affect the Solubility of Zn and Other Bivalent Cations in the Digestive Tract of Ruminants In Vitro ». Animals 11, n^o 3 (19 mars 2021) : 877. http://dx.doi.org/10.3390/ani11030877.

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Ruminants ingest large quantities of clay minerals along with inorganic soil constituents in roughages. The layered structure of clay minerals, however, may adsorb cations and may, thus, interfere with the ruminants’ supply of essential trace metals, such as Zn, Mn, Cu, and Fe. As quantitative knowledge about interactions between clay ingestion and essential trace metal metabolism are largely lacking, this in vitro study focussed on the effect of clay on the solubility of dietary Zn and other bivalent trace metals in the digestive tract of ruminants. Therefore, buffered rumen fluid was used for the simulation of ruminal conditions (RC), acidified rumen fluid (pH 2) was used for abomasal conditions (AC), and duodenal chyme was used for duodenal conditions (DC). These media were added with gradient levels of zinc and incubated at 39 °C for 24 h in the absence or presence of clay minerals. Soluble Zn, Cu, Mn, and Fe were derived by centrifugation (10,000× g) of incubated media, and the supernatants were analysed. Clay depressed the solubility of added Zn in ruminal (65.3% vs. 16.5%), abomasal (97.7% vs. 33.7%), and duodenal conditions (41.3% vs. 21.1%), the results of which were statistically significant (p < 0.001). Moreover, clay reduced dissolved Cu (µg/mL) (RC: 0.13 vs. 0.10; AC: 0.16 vs. 0.13; DC: 0.10 vs. 0.08) and Mn (µg/mL) (RC: 3.00 vs. 1.80; AC: 5.53 vs. 4.80; DC: 3.18 vs. 1.77) (p < 0.05 in all cases). The presence of clay minerals increased the concentrations of solubilised Fe (µg/mL) in abomasal (1.80 vs. 2.86, p < 0.05) and duodenal conditions (1.76 vs. 2.67; p < 0.05). In total, the present in vitro study demonstrates the potential of clay minerals ingested with ruminant feeds for depressing the solubility of dietary Zn, as well as the depression of dietary Cu and Mn along the passage of the digesta from the rumen until the duodenum. Additionally, clay minerals may release Fe into the digesta.

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Blume, Astrid, Jesus Angulo, Thorsten Biet, Hannelore Peters, Andrew J. Benie, Monica Palcic et Thomas Peters. « Fragment-based Screening of the Donor Substrate Specificity of Human Blood Group B Galactosyltransferase Using Saturation Transfer Difference NMR ». Journal of Biological Chemistry 281, n^o 43 (21 août 2006) : 32728–40. http://dx.doi.org/10.1074/jbc.m600424200.

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Saturation transfer difference NMR experiments on human blood group B α-(1,3)-galactosyltransferase (GTB) for the first time provide a comprehensive set of binding epitopes of donor substrate analogs in relation to the natural donor UDP-Gal. This study revealed that the enzyme binds several UDP-activated sugars, including UDP-Glc, UDP-GlcNAc, and UDP-GalNAc. In all cases, UDP is the dominant binding epitope. To identify the minimum requirements for specific binding, a detailed analysis utilizing a fragment-based approach was employed. The binding of donor substrate to GTB is essentially controlled by the base as a “molecular anchor.” Uracil represents the smallest fragment that is recognized, whereas CDP, AMP, and GDP do not exhibit any significant binding affinity for the enzyme. The ribose and β-phosphate moieties increase the affinity of the ligands, whereas the pyranose sugar apparently weakens the binding, although this part of the molecule controls the specificity of the enzyme. Accordingly, UDP represents the best binder. The binding affinities of UDP-Gal, UDP-Glc, and UMP are about the same, but lower than that of UDP. Furthermore, we observed that β-d-galactose and α-d-galactose bind weakly to GTB. Whereas β-d-galactose binds to the acceptor and donor sites, it is suggested that α-d-galactose occupies a third hitherto unknown binding pocket. Finally, our experiments revealed that modulation of enzymatic activity by metal ions critically depends on the total enzyme concentration, raising the question as to which of the bivalent metal cations Mg2+ and Mn2+ is more relevant under physiological conditions.

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Chavagnat, Frederic, Michael G. Casey et Jacques Meyer. « Purification, Characterization, Gene Cloning, Sequencing, and Overexpression of Aminopeptidase N from Streptococcus thermophilus A ». Applied and Environmental Microbiology 65, n^o 7 (1 juillet 1999) : 3001–7. http://dx.doi.org/10.1128/aem.65.7.3001-3007.1999.

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ABSTRACT The general aminopeptidase PepN from Streptococcus thermophilus A was purified to protein homogeneity by hydroxyapatite, anion-exchange, and gel filtration chromatographies. The PepN enzyme was estimated to be a monomer of 95 kDa, with maximal activity on N-Lys–7-amino-4-methylcoumarin at pH 7 and 37°C. It was strongly inhibited by metal chelating agents, suggesting that it is a metallopeptidase. The activity was greatly restored by the bivalent cations Co2+, Zn2+, and Mn2+. Except for proline, glycine, and acidic amino acid residues, PepN has a broad specificity on the N-terminal amino acid of small peptides, but no significant endopeptidase activity has been detected. The N-terminal and short internal amino acid sequences of purified PepN were determined. By using synthetic primers and a battery of PCR techniques, the pepN gene was amplified, subcloned, and further sequenced, revealing an open reading frame of 2,541 nucleotides encoding a protein of 847 amino acids with a molecular weight of 96,252. Amino acid sequence analysis of thepepN gene translation product shows high homology with other PepN enzymes from lactic acid bacteria and exhibits the signature sequence of the zinc metallopeptidase family. The pepN gene was cloned in a T7 promoter-based expression plasmid and the 452-fold overproduced PepN enzyme was purified to homogeneity from the periplasmic extract of the host Escherichia coli strain. The overproduced enzyme showed the same catalytic characteristics as the wild-type enzyme.

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Yakubu, Abdulmojeed, Daniels Alade et Ndubuisi Dim. « Molecular analysis of solute carrier family 11 member a1 (Slc11a1) gene in ruminants and non-ruminants using computational method ». Genetika 46, n^o 3 (2014) : 925–34. http://dx.doi.org/10.2298/gensr1403925y.

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Solute carrier family 11 member a1 gene (Slc11a1) previously known as natural resistance-associated macrophage protein 1 (Nramp1) is a gene of member of family of metal ion-transport protein. The cellular expression is restricted to phagocytic cells. Slc11a1 delivers bivalent metal cations from the cytosol into acidic endosomal and lysosomal compartments where Fenon and Haber-Weiss reaction generates toxic antimicrobial radicals for direct antimicrobial activity against harmful microorganisms. The present study was undertaken with the objective of analyzing Slc11a1 gene to gain insight into the evolutionary proximity and divergence as well as the polymorphism of this gene in ruminants and non-ruminants including the attendant effects of the genetic variants on the function of the Slc11a1 protein. Thirty Slc11a1 gene sequences of 6 mammalian species classified as ruminant (goat, sheep, cattle, Bubalus bubalis and Bubalus carabanensis) and non-ruminant (swine and horse) animals were investigated. The length of the Slc11a1 gene varied from 448-2,357. There was substantial genetic variation and polymorphism in the aligned sequences of Slc11a1 gene within and across species. Functional analysis of non-synonymous mutations in cattle revealed that twenty five of the amino acid substitutions at the peptide binding region could be beneficial, (E36G), (T52A), (N161S) and (V248I) were likely to be beneficial while only (Q312K) was harmful. In horse, two of the amino acid mutations were harmful, two were likely to be harmful, one was undecided, four were likely beneficial and the rest twenty were beneficial. The phylogenetic trees showed some form of proximity and differentiation in Slc11a1 sequences within and across species. The present information on the polymorphism of Slc11a1 gene might be exploited in the search for association with disease resistance in Nigerian livestock species.

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Drews, Janina, Rudi Ruben Maça, Liping Wang, Johannes Wiedemann, J. Alberto Blázquez, Zhirong Zhao-Karger, Maximilian Fichtner, Timo Danner et Arnulf Latz. « Continuum Modelling As Tool for Optimizing the Cell Design of Magnesium Batteries ». ECS Meeting Abstracts MA2022-02, n^o 4 (9 octobre 2022) : 461. http://dx.doi.org/10.1149/ma2022-024461mtgabs.

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Magnesium-based next-generation batteries are of great interest since magnesium is not only very abundant, which allows economic and sustainable applications, but also less prone to dendrite formation than many other metals. Together with the bivalency of the magnesium cations the resulting possibility to safely use a metal anode enables batteries with high specific capacities. However, for a successful commercialization of magnesium batteries there are still some challenges to overcome. The high charge density of the bivalent cation causes strong coulomb interactions with anions and solvent molecules. Therefore, magnesium salts are prone to form ion pairs and bigger clusters – especially at high concentrations, which may adversely affect the transport in the electrolyte and the electrochemical reaction at the electrode.[1] Moreover, energetic barriers for desolvation and solid-state diffusion of the double-charged magnesium ion are usually very high, which can have a crucial impact on the battery performance. Former can significantly hinder the electron-transfer reaction,[2] whereas latter makes the choice of suitable cathode materials very challenging. Consequently, a good understanding of the limiting processes in rechargeable magnesium batteries is key to develop novel high-capacity / high-voltage cathode materials. For instance, it is well-known that the morphology of an intercalation material can strongly influence the battery performance and smaller particles as well as thinner electrodes are common strategies for avoiding adverse effects of transport limitations. However, high mass loadings as well as suitable separators are still essential bottlenecks for commercialization of magnesium-ion batteries. Up to date Chevrel phase (CP) Mo6S8 is considered as benchmark intercalation cathode and Mg[B(hfip)4]2 / DME is seen as most promising chloride-free magnesium electrolyte.[3,4] In our contribution we carefully study this model system of a magnesium-ion battery to get a better understanding of how to overcome undesired limitations. Therefore, we present a newly-developed continuum model, which is able to describe the complex intercalation process of magnesium cations into a CP cathode. The model considers not only the different thermodynamics and kinetics of the two intercalation sites of Mo6S8 and their interplay but also the impact of the desolvation on the electrochemical reactions and possible ion agglomeration. The parameterization and validation of the model is based on DFT calculations and experimental data. Different kind of (transport) limitations and their impact on the battery performance are studied in detail. All in all, the combination of different modelling techniques with experimental measurements provides important insights into the operation of magnesium ion batteries and enables an optimization of the cell design. Acknowledgements This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 824066 (E-MAGIC). Furthermore, this work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm-Karlsruhe) and was funded by the German Research Foundation (DFG) under Project ID 390874152 (POLiS Cluster of Excellence). The simulations were carried out at JUSTUS 2 cluster supported by the state of Baden-Württemberg through bwHPC and the German Research Foundation (DFG) through grant No INST 40/575-1 FUGG. References Drews, T. Danner, P. Jankowski et al., ChemSusChem, 3 (2020), 3599-3604. Drews, P. Jankowski, J. Häcker et al., ChemSusChem, 14 (2021), 4820-4835. Aurbach, Z. Lu, A. Schlechter et al., Nature, 407 (2000), 724-727. Zhao-Karger, R. Liu, W. Dai et al., ACS Energy Lett. 3 (2018), 2005-2013.

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Kurochkina, Anna S., et Alla A. Krasnoshtanova. « Study of the sorption capacity of soluble forms of yeast beta-glucan ». Butlerov Communications 63, n^o 9 (30 septembre 2020) : 43–50. http://dx.doi.org/10.37952/roi-jbc-01/20-63-9-43.

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Beta-glucans are polysaccharides that consist of D-glucose residues linked together in the main and side chains by glycosidic bonds. They are obtained from plant and microbial raw materials. Beta-glucans obtained from various sources differ in molecular weight, backbone length, branching of additional chains and their number. Beta-(1,3,1,6)-glucan from the yeast Saccharomyces cerevisiae has the highest physiological activity. The soluble fraction of beta-glucan has a higher physiological activity than its insoluble fraction. As a rule, soluble beta-glucans appear to be more potent immunostimulants than insoluble ones. In this regard, obtaining soluble forms of beta-glucan from yeast is relevant. The purpose of this work was to study the effect of the content of the soluble fraction in yeast beta-glucan on the ability to adsorb heavy metal ions, mycotoxins and cholesterol. Evaluation of the effectiveness of ultrasonic treatment for obtaining soluble forms of yeast beta-glucan was carried out. It was found that the maximum content of the soluble fraction, equal to 95%, at a frequency of ultrasonic treatment of 85 kHz for a laboratory sample of beta-glucan, is achieved with a treatment time of 20 min, and for a commercial one – in 30 min. The sorption properties of soluble forms of yeast beta-glucan with different content of the soluble fraction in relation to cholesterol, aflatoxin and bivalent copper cations were studied. The sorption capacity of samples of laboratory and commercial preparations of beta-glucan was determined for the above compounds. It was found that an increase in the content of the soluble fraction to more than 50% does not lead to a noticeable increase in the sorption capacity. It was shown that purified samples of beta-glucan have higher sorption characteristics.

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Singare, Pravin U., Akmal L. Khan Mohammed et N. N. Dixit. « Study on Preferential Selectivity of Nuclear Grade Resin Indion-223 towards some Bivalent Ions ». International Letters of Chemistry, Physics and Astronomy 34 (30 mai 2014) : 11–21. http://dx.doi.org/10.56431/p-4b9z2i.

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In the present paper attempts are made to understand the selectivity of nuclear grade cation exchange resin Indion-223 in H+ form towards Ca2+ and Mg2+ bivalent ions in the solution based on thermodynamic concept. It was observed that with rise in temperature the equilibrium constant K values for H+/Ca2+ uni-bivalet ion exchange reactions increases from 0.000397 to 0.000639. Similarly for H+/Mg2+ uni-bivalet ion exchange reactions the equilibrium constant K values increases from 0.000177 to 0.000333. The increase in equilibrium constant values with rise in temperature indicate endothermic ion exchange reactions having the enthalpy change values of 38.92 and 51.46 kJ/ mol respectively. The difference in K values and enthalpy values were used to predict the selectivity behaviour of the resin towards the Ca2+ and Mg2+ bivalent ions in the solution. The thermodynamic concept of the present study can be applied to understand the selectivity behaviour of different nuclear as well as non-nuclear grade resins towards wide range of ionic species present in the exchanging liquid medium.

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Burda, Jaroslav V., Jiří Šponer et Pavel Hobza. « Ab Initio Study of the Interaction of Guanine and Adenine with Various Mono- and Bivalent Metal Cations (Li+, Na+, K+, Rb+, Cs+ ; Cu+, Ag+, Au+ ; Mg2+, Ca2+, Sr2+, Ba2+ ; Zn2+, Cd2+, and Hg2+) ». Journal of Physical Chemistry 100, n^o 17 (janvier 1996) : 7250–55. http://dx.doi.org/10.1021/jp952941h.

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Renger, G., H. M. Gleiter, E. Haag et F. Reifarth. « Photosystem II : Thermodynamics and Kinetics of Electron Transport from QA- to QB(QB- ) and Deleterious Effects of Copper(II) ». Zeitschrift für Naturforschung C 48, n^o 3-4 (1 avril 1993) : 234–40. http://dx.doi.org/10.1515/znc-1993-3-419.

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Studies on thermodynamics and kinetics of electron transfer from QA- to QB(QB-) were performed by monitoring laser flash induced changes of the relative fluorescence emission as a function of temperature (220 K < T < 310 K) in isolated thylakoids and PS II membrane fragments.In addition, effects of bivalent metal ions on PS II were investigated by measuring conventional fluorescence induction curves, oxygen evolution, manganese content and atrazine binding mostly in PS II membrane fragments. It was found: a) the normalized level of the fluorescence remaining 10 s after the actinic flash (Ft/F0) steeply increases at temperatures below -10 to - 20 °C, b) the fast phase of the transient fluorescence change becomes markedly retarded with decreasing temperatures, c) among different cations (Cu2+, Zn2+, Cd2+, Ni2+, Co2+) only Cu2+ exhibits marked effects in the concentration range below 100 μᴍ and d) Cu2+ decreases the normalized variable fluorescence, inhibits oxygen evolution and diminishes the affinity to atrazine binding without affecting the number of binding sites. The content of about four manganeses per functionally competent oxygen evolving complex is not changed by [Cu2+] < 70 μᴍ.Based on these findings it is concluded: i) a temperature dependent equilibrium between an inactive (I) and active (A) state of QA- reoxidation by QB(QB- ) is characterized by standard enthalpies ΔH° of 95 kJ mol-1 and 60 kJ mol-1 and standard entropies ΔS° of 370 kJ K-1 mol-1 and 240 kJ K-1 mol-1 in isolated thylakoids and PS II membrane fragments, respectively, ii) the activation energies of QA- reoxidation by plastoquinone bound to the QB site are about 30 kJ mol-1 (thylakoids) and 40 kJ mol-1 (PS II membrane fragments) in 220 K < T < 300 K, and iii) Cu2+ causes at least a two-fold effect on PS II by modifying the atrazine binding affinity at lower concentrations ( ~ 5 μᴍ) and interference with the redox active tyrosine Yz at slightly higher concentration ( ~ 10 μᴍ) leading to blockage of oxygen evolution.

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WHEELER, Kerry A., Heather K. LAMB et Alastair R. HAWKINS. « Control of metabolic flux through the quinate pathway in Aspergillus nidulans ». Biochemical Journal 315, n^o 1 (1 avril 1996) : 195–205. http://dx.doi.org/10.1042/bj3150195.

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The quinic acid utilization (qut) pathway in Aspergillus nidulans is a dispensable carbon utilization pathway that catabolizes quinate to protocatechuate via dehydroquinate and dehydroshikimate (DHS). At the usual in vitro growth pH of 6.5, quinate enters the mycelium by means of a specific permease and is converted into PCA by the sequential action of the enzymes quinate dehydrogenase, 3-dehydroquinase and DHS dehydratase. The extent of control on metabolic flux exerted by the permease and the three pathway enzymes was investigated by applying the techniques of Metabolic Control Analysis. The flux control coefficients for each of the three quinate pathway enzymes were determined empirically, and the flux control coefficient of the quinate permease was inferred by use of the summation theorem. These measurements implied that, under the standard growth conditions used, the values for the flux control coefficients of the components of the quinate pathway were: quinate permease, 0.43; quinate dehydrogenase, 0.36; dehydroquinase, 0.18; DHS dehydratase, < 0.03. Attempts to partially decouple quinate permease from the control over flux by measuring flux at pH 3.5 (when a significant percentage of the soluble quinate is protonated and able to enter the mycelium without the aid of a permease) led to an increase of approx. 50% in the flux control coefficient for dehydroquinase. Taken together with the fact that A. nidulans has a very efficient pH homoeostasis mechanism, these experiments are consistent with the view that quinate permease exerts a high degree of control over pathway flux under the standard laboratory growth conditions at pH 6.5. The enzymes quinate dehydrogenase and 3-dehydroquinase have previously been overproduced in Escherichia coli, and protocols for their purification published. The remaining qut pathway enzyme DHS dehydratase was overproduced in E. coli and a purification protocol established. The purified DHS dehydratase was shown to have a Km of 530 μM for its substrate DHS and a requirement for bivalent metal cations that could be fulfilled by Mg2+, Mn2+ or Zn2+. All three qut pathway enzymes were purified in bulk and their elasticity coefficients with respect to the three quinate pathway intermediates were derived over a range of concentrations in a core tricine/NaOH buffer, augmented with necessary cofactors and bivalent cations as appropriate. Using these empirically determined relative values, in conjunction with the connectivity theorem, the relative ratios of the flux control coefficients for the various quinate pathway enzymes, and how this control shifts between them, was determined over a range of possible metabolite concentrations. These calculations, although clearly subject to caveats about the relationship between kinetic measurements in vitro and the situation in vivo, were able to successfully predict the hierarchy of control observed under the standard laboratory growth conditions. The calculations imply that the hierarchy of control exerted by the quinate pathway enzymes is stable and relatively insensitive to changing metabolite concentrations in the ranges most likely to correspond to those found in vivo. The effects of substituting the type I 3-dehydroquinases from Salmonella typhi and the A. nidulans AROM protein (a pentadomain protein catalysing the conversion of 3-deoxy-D-arabinoheptulosonic acid 7-phosphate into 5-enolpyruvylshikimate 3-phosphate), and the Mycobacterium tuberculosis type II 3-dehydroquinase, in the quinate pathway were investigated and found to have an effect. In the case of S. typhi and A. nidulans, overproduction of heterologous dehydroquinase led to a diminution of pathway flux caused by a lowering of in vivo quinate dehydrogenase levels. With M. tuberculosis, however, quinate dehydrogenase levels increased above those of the wild type. We speculate that these changes in quinate pathway enzyme activities may be due to changes in the pool sizes of quinate and dehydroquinate.

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Bye, R. « Interferences from bivalent cations in the determination of selenium by hydride-generation and atomic-absorption spectrometry A discussion of the claim that the metal ions are reduced to the metallic state by sodium borohydride ». Talanta 33, n^o 8 (août 1986) : 705–6. http://dx.doi.org/10.1016/0039-9140(86)80165-5.

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Gao, Xiaokang, Yunzhe Li, Yu Qin, Enhui Chen, Qian Li, Xinfeng Zhao, Liujiao Bian et al. « Reversible and oriented immobilization of histidine-tagged protein on silica gel characterized by frontal analysis ». RSC Advances 5, n^o 31 (2015) : 24449–54. http://dx.doi.org/10.1039/c5ra01012h.

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Utilizing N,N′-bis(carboxymethyl)-L-lysine (ANTA) combined with bivalent metal cation Ni²⁺, which leaving free sites for the reversible binding of gene recombinant histidine-tagged β₂-adrenoceptor onto silica gel.

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Fournier, Françoise, et Michel Fournier. « Transferts d'électrons assistés par les métaux de transition:influence de la nature du cation métallique sur la réduction de composés carbonylés en milieu aprotique ». Canadian Journal of Chemistry 64, n^o 5 (1 mai 1986) : 881–90. http://dx.doi.org/10.1139/v86-146.

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The pinacolisation of ketones is enhanced when a bivalent transition metal cation is present. This phenomenon is general and occurs with Cr2+, Mn2+, Fe2+, Co2+, Zn2+ but not with Ni2+. The cathodic reduction leads to α-glycols with a good yield, without any resin production, and at a less negative potential than that of the ketone itself. The distribution of all isolated compounds is dependent on the Lewis character-acidity and complexing power of the metallic cation. Thus, for the dimerization, the greatest specificity is generally observed when Fe2+ is present. For the chalcone, the better stereoselectivity is obtained with Zn2+. No evidence of initial carbonyl complex of the metal ion was shown.

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Sherys, A. Y., A. N. Gurov et V. B. Tolstoguzov. « Water-insoluble triple complexes : Bovine serum albumin-bivalent metal cation-alginate ». Carbohydrate Polymers 10, n^o 2 (janvier 1989) : 87–102. http://dx.doi.org/10.1016/0144-8617(89)90059-3.

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Anbarasi, C. Mary, et Susai Rajendran. « Surface Protection of Carbon Steel by Hexanesulphonic Acid-Zinc Ion System ». ISRN Corrosion 2014 (19 mars 2014) : 1–8. http://dx.doi.org/10.1155/2014/628604.

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Inhibition of corrosion of carbon steel in dam water by hexanesulphonic acid as its sodium salt C6H13SO3Na (SHXS) in the absence and presence of a bivalent cation zinc ion (Zn2þ) has been investigated using weight loss method. Results of weight loss method indicate that inhibition efficiency (IE) increased with increase of inhibitor concentration. Polarization study reveals that SHXS-Zn2+ system controls the cathodic reaction predominantly. AC impedance spectra reveal that a protective film is formed on the metal surface. The nature of the metal surface has been analysed by Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM).

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Khasbaatar, D., et Ung Su Choi. « Fourier Transform Infrared Spectroscopy Study on Cation adsorption on Viscose Rayon Succinate ». Mongolian Journal of Chemistry 12 (24 septembre 2014) : 136–41. http://dx.doi.org/10.5564/mjc.v12i0.189.

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Ion-exchange materials have been considered as suitable material for the recovery of heavy metals in water. A viscose rayon succinate, synthesized from viscose rayon and succinic anhydride in presence of DMSO, to remove trace bivalent metal ions such as Ag+, Cu2+, Ni2+, Pb2+, Zn2+ and Cr3+, was studied using FT-IR for the behavior of metal adsorption. Both esterification and carboxyl bonding of viscose rayon succinate were assigned essentially at 1729 and 1693cm-1, respectively. And the essential band of bonding between metal and the material was determined at 1625cm-1. The available adsorption capacity of this fiber was 6.2 mequiv/g. The adsorption of metal ions on the viscose rayon succinate follows the order of Cu2+>Cr3+>Ni2+>Pb2+>Zn2+>Ag+ with maximum adsorptions capacities 4.2, 1.42, 0.91, 0.83, 0.69 and 0.35 mmol/g, respectively.DOI: http://dx.doi.org/10.5564/mjc.v12i0.189 Mongolian Journal of Chemistry Vol.12 2011: 136-141

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Pisani, Michela, Giovanna Mobbili, Immacolata F. Placentino, Arianna Smorlesi et Paolo Bruni. « Biophysical Characterization of Complexes of DNA with Mixtures of the Neutral Lipids 1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine-N-hexanoylamine or 1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine-N-dodecanoylamine and 1,2-Dioleoyl-sn-glycero-3-phosphocholine in the Presence of Bivalent Metal Cations for DNA Transfection ». Journal of Physical Chemistry B 115, n^o 34 (septembre 2011) : 10198–206. http://dx.doi.org/10.1021/jp202577u.

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Navaratnam, N., S. S. Virk, S. Ward et N. J. Kuhn. « Cationic activation of galactosyltransferase from rat mammary Golgi membranes by polyamines and by basic peptides and proteins ». Biochemical Journal 239, n^o 2 (15 octobre 1986) : 423–33. http://dx.doi.org/10.1042/bj2390423.

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Galactosyltransferase (EC 2.4.1.22) requires bivalent metal ions for its activity. However, preparations of this enzyme solubilized from Golgi membranes of lactating rat mammary gland were shown to be activated not only by Mn2+, Ca2+ and Mg2+, but also by spermine, spermidine, lysyl-lysine, ethylenediamine and other diaminoalkanes, and by a range of basic proteins and peptides, including clupeine, histone, polylysine, ribonuclease, pancreatic trypsin inhibitor, cytochrome c, melittin, avidin and myelin basic protein. Both N-acetyl-lactosamine synthetase and lactose synthetase activities were enhanced. A basic protein fraction was isolated from bovine milk and shown to activate galactosyltransferase at low concentrations. The polyanions ATP, casein, chondroitin sulphate and heparin reversed the activation of galactosyltransferase by several of the above substances. Galactosyltransferase, assayed as a lactose synthetase, showed a 10-fold greater affinity for glucose when Mn2+ ions were replaced by clupeine or by ribonuclease as cationic activator. Evidence was obtained for the presence of an endogenous cationic activator in solubilized Golgi membrane preparations which evoked a similar low apparent Km, glucose. The findings are discussed in the light of cationic activations of glycosyltransferases generally, of the porous nature of the Golgi membrane, and of the unlikelihood of bivalent metal ions being the physiological activators of galactosyltransferase. It is suggested that the natural cationic activator of lactose synthetase may be a secretory protein acting in a manner analogous to the enzyme's activation by alpha-lactalbumin. A scheme is proposed for the two-stage synthesis of lactose and phosphorylation of casein within the cell, to accommodate the apparent incompatibility of these two processes.

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Kraskouskaya, Dziyana, Joel A. Drewry, Eugenia Duodu, Steven Burger, James Eaton, G. Andrés Cisneros et Patrick T. Gunning. « Exploring the structural determinants of selective phosphopeptide recognition using bivalent metal-coordination complexes ». MedChemComm 4, n^o 1 (2013) : 289–92. http://dx.doi.org/10.1039/c2md20342a.

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We demonstrate that Lewis acidic coordination complexes equipped with cationic binding groups might be best utilized as selective receptors for binding phosphopeptides with anionic side chain residues proximal to the phosphorylated residue.

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Жильцов, И. В. « Natural Factors That Affect the Level of Beta-Lactamase Activity of Human Serum ». Лабораторная диагностика. Восточная Европа, n^o 1-2 (21 avril 2020) : 60–67. http://dx.doi.org/10.34883/pi.2020.9.1.028.

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Введение. Как было установлено нами ранее, человеческий сывороточный альбумин обладает собственной бета-лактамазной активностью и способен гидролизовать бета-лактамную связь в молекулах многих антибиотиков из одноименной группы. Цель. Установить, насколько естественные факторы, такие как рН крови, температура, время суток и др., влияют на уровень бета-лактамазной активности сыворотки крови человека. Материалы и методы. Для количественного определения бета-лактамазной активности сыворотки крови использовали спектрофотометрический метод, основанный на регистрации распада бета-лактамной связи нитроцефина (в том числе при изменении рН раствора хромогена, внесении в реакционную среду раствора ЭДТА, изменении температуры инкубируемой среды). Использованы сыворотки крови практически здоровых людей (доноров), а также пациентов реанимационного отделения Витебской областной инфекционной больницы. Результаты и обсуждение. Установлено, что бета-лактамазная активность сыворотки крови характеризуется оптимумом рН в районе 9,0, а при изменении рН с 7,0 до 8,0 меняется с минимальных до субмаксимальных значений. При повышении температуры инкубации с 36 С до 42 С бета-лактамазная активность сыворотки крови возрастает на 45. Присутствие двухвалентных катионов металлов практически не оказывает влияния на уровень бета-лактамазной активности сыворотки крови. Уровень бета-лактамазной активности сыворотки крови постепенно снижается с возрастом. По крайней мере у некоторых пациентов возможны значительные (до 20) суточные колебания бета-лактамазной активности сыворотки крови. Выводы. Бета-лактамазная активность сыворотки крови является сложным интегральным параметром, зависящим от многих эндогенных факторов, что затрудняет клиническую интерпретацию получаемых результатов. Introduction. As we previously discovered, human serum albumin has its own beta-lactamase activity and can hydrolyze the beta-lactam bond in the molecules of many antibiotics from this group. Purpose. To determine how natural factors, such as blood pH, temperature, time of the day, etc., affect the level of beta-lactamase activity of human blood serum. Materials and methods. To quantitatively determine the serum beta-lactamase activity, a spectrophotometric method was used on the base of detection of hydrolysis of the nitrocephin beta-lactam bond (the pH of the chromogen solution was variated, the EDTA solution was added to the reaction medium, and the incubation temperature was changed if necessary). For our experiments, we used the blood serum of healthy donors, as well as patients of the intensive care unit of the Vitebsk regional infectious diseases hospital. Results and discussion. It was found that the serum beta-lactamase activity is characterized by pH optimum near 9.0 when the pH changes from 7.0 to 8.0, the beta-lactamase activity level changes from minimum to submaximal values. If the temperature of incubation increases from 36 C to 42 C, the beta-lactamase activity of blood serum increases by 45. The presence of bivalent metal cations produces practically no effect on the level of beta-lactamase activity of blood serum. The level of beta-lactamase activity of blood serum gradually decreases with aging. In at least some patients, significant (up to 20) diurnal fluctuations of the serum beta-lactamase activity are possible. Conclusions. Serum beta-lactamase activity is a complex integral parameter, which depends on many endogenous factors that complicate the clinical interpretation of its levels.

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Dubey, S. K., et L. C. Rai. « Toxicity of chromium and tin toAnabaena doliolum Interaction with bivalent cations ». Biology of Metals 3, n^o 1 (1990) : 8–13. http://dx.doi.org/10.1007/bf01141170.

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