Influence of multiple metal ions on beta-amyloid aggregation and dissociation on a solid surface

Recently discovered evidences suggest that precipitation of Alzheimer's beta-amyloid (Abeta) peptide and the toxicity in Alzheimer's disease (AD) are caused by abnormal interactions with neocortical metal ions, especially Zn2+, Cu2+, and Fe3+. While many studies had focused on the role of a "single" metal ion and its interaction with Abeta peptides, such studies involving "multiple" metal ions have hardly been explored. Here, to explore the nature of codeposition of different metals, two or more metal ions along with Abeta were incubated over a solid template prepared by immobilizing Abeta42 oligomers. The influence of Zn2+,Cu2+, and Fe3+ on Abeta aggregation was investigated by two approaches: co-incubation and sequential addition. Our results using ex situ AFM, ThT-induced fluorescence, and FTIR spectroscopy indicated that the co-incubation of Cu2+, Zn2+, and Fe3+ significantly altered the morphology of aggregates. A concentration dependence study with mixed metal ions suggested that Zn2+ was required at much lower concentrations than Cu2+ to yield nonfibrillar amorphous Abeta deposits. In addition, sequential addition of Zn2+ or Cu2+ on fibrillar aggregates formed by Fe3+ demonstrated that Zn2+ and Cu2+ could possibly change the conformation of the aggregates induced by Fe3+. Our findings elucidate the coexistence of multiple metal ions through their interactions with Abeta peptides or its aggregates.     

Accumulation and removal of heavy metal ions by insolubilized-DNA and its interaction.

DNA was immobilized onto a porous glass bead by a treatment with UV irradiation. The immobilized DNA was insoluble in water and used for accumulation of heavy metal ion. When DNA-immobilized glass bead was added into aqueous solution containing heavy metal ions, such as Hg2+, Cd2+, Pb2+, Zn2+, Cu2+ and Fe3+, the concentration of these metal ions in the solution was decreased. However, the concentration of Mg2+ in the solution was not affected by the addition of the DNA-immobilized glass bead. These results suggested that UV-irradiated DNA selectively accumulated heavy metal ions.     

Heparin-binding properties of lactoferrin and lysozyme.

1. Binding of biotin-heparin to immobilized lactoferrin and lysozyme was optimum at pH 6.0, 100 mM NaCl. Complex interactions between NaCl and CaCl2 concentrations were observed for heparin binding to both proteins. 2. The metal ions Cu2+, Zn2+, Fe2+ and Fe3+ inhibited heparin binding, with half-maximal inhibition of binding to lactoferrin occurring between 600 microM and 1 mM and for lysozyme between 500 and 800 microM. 3. Binding of biotin-heparin to both proteins was inhibited to varying degrees by heparin, heparan sulfate, chondroitin sulfate A, dextran sulfate and DNA.     

金属离子对蜡蚧菌几丁质酶活力的影响

以蜡蚧菌(Ll)发酵液为材料,经分离纯化获得Ll几丁质酶(EC3.2.1.14)制剂.研究了金属离子对Ll几丁质酶活力的影响.结果表明,K+、Mg2+、Zn2+、Ca2+和Fe3+对几丁质酶活性有明显的促进作用,而Na+和Cu2+完全抑制几丁质酶的活性;Mn2+在低浓度时对酶有激活作用,随着浓度的升高表现出抑制作用;Fe2+和Ba2+的浓度低于0.5 mmol/L时对酶起抑制作用,而高于该浓度时则对酶有激活作用.     

Characteristics of the ionic composition and ultrastructure of Bordetella pertussis in controlled regulation of the mineral element content in a growth medium

The content of trace elements necessary for the normal growth of bacteria was found to have no effect on the intracellular concentration of Ca2+ and Al3+. The content of Cu2+, Fe3+, Mn2+, Mg2+ was considerably reduced. The addition of Mg2+ at different concentrations to this culture medium stimulated the capacity of cells for accumulating not only Mg2+, but also some other ions. Their maximum intracellular concentration was observed when the concentration of Mg2+ in the culture medium was 41 mM. The growth of microbial cells in the standard culture medium containing Mg2+ at a concentration of 4 mM was accompanied by the increased consumption of elements actively participating in redox reactions (Cu2+, Fe3+, Mn2+). Shifts in the ionic composition of microbial cells were manifested by the morphological features of B. pertussis, linked with the increased synthesis of crystalloid structures. The influence of Mn2+, Al3+, Zn2+ at different concentrations on the ionic composition and morphology of B. pertussis was studied.     

Differences in the protein fluorecence of the two iron(III)-binding sites of ovotransferrin.

1. Changes in the tryptophan fluorescence and the visible absorption spectrum resulting from the combination of apo-ovotransferrin with Fe3+, F,E2+, Cu2+, Zn2+, Mn2+, and Cd2+were measured. 2. As expected for a radiationless transfer of electronic excitation energy, only the ions Fe3+, Fe2+and Cu2+, which gave complexes with large extinctions between 300 and 370nm, resulted in large decreases in trytophan fluorescence. 3. The decrease in protein fluorescence was non-linear with increasing occupancy of the Fe3+ -and Cu2+ - binding sites. The decrease in fluorescence on binding of Fe3+ was biphasic and showed that the two metal-binding sites were being occupied sequentially at pH7.4-8.4. The first site reacted with Fe3+ instantaneously, the second was occupied over a minute. 5. The nonidentity of the two sites was also demonstrated by the preparation of a stable hybrid containing both Cu2+ and Zn2+.h Cu2+ and Zn2+     

Differential effects of monovalent, divalent and trivalent metal ions on rat brain hexokinase

The effects of monovalent (Li+, Cs+) divalent (Cu2+, Ca2+, Sr2+, Ba2+, Zn2+, Cd2+, Hg2+, Pb2+, Mn2+, Fe2+, Co2+, Ni2+) and trivalent (Cr3+, Fe3+, Al3+) metals ions on hexokinase activity in rat brain cytosol were compared at 500 microM. The rank order of their potency as inhibitors of brain hexokinase was: Cr3+ (IC50 = 1.3 microM) greater than Hg2+ = Al3+ greater than Cu2+ greater than Pb2+ (IC50 = 80 microM) greater than Fe3+ (IC50 = 250 microM) greater than Cd2+ (IC50 = 540 microM) greater than Zn2+ (IC50 = 560 microM). However, at 500 microM Co2+ slightly stimulated brain hexokinase whereas the other metal ions were without effect. That inhibition of brain glucose metabolism may be an important mechanism in the neurotoxicity of metals is suggested.     

Interaction of DNA with divalent metal ions

The interaction between the native DNA macromolecules and Ca2+, Mn2+, Cu2+ ions in solutions of low ionic strength (10(-3) M Na+) is studied using the methods of differential UV spectroscopy and CD spectroscopy. It is shown that the transition metal ions Mn2+ exercise binding to the nitrogen bases of DNA at concentrations approximately 5 x 10(-6) M and form chelates with guanine of N7-Me(2+)-O6 type. Only at high concentrations in solution (5 x 10(-3) M) do Ca2+ ions interact with the nitrogen bases of native DNA. In the process of binding to Ca2+ and Mn2+ the DNA conformation experiences some changes under which the secondary structure of the biopolymer is within the B-form family. The DNA transition to the new conformation is revealed by its binding to Cu2+ ions.     

Oxidoreductase activities of polyclonal IgGs from the sera of Wistar rats are better activated by combinations of different metal ions

It was shown that IgGs purified from the sera of healthy Wistar rats contain several different bound Me2+ ions and oxidize 3,3'-diaminobenzidine through a H2O2-dependent peroxidase and H2O2-independent oxidoreductase activity. IgGs have lost these activities after removing the internal metal ions by dialysis against EDTA. External Cu2+ or Fe2+ activated significantly both activities of non-dialysed IgGs containing different internal metals (Fe > or = Pb > or = Zn > or = Cu > or = Al > or = Ca > or = Ni > or = Mn > Co > or = Mg) showing pronounced biphasic dependencies corresponding to approximately 0.1-2 and approximately 2-5 mM of Me2+, while the curves for Mn2+ were nearly linear. Cu2+ alone significantly stimulated both the peroxidase and oxidoreductase activities of dialysed IgGs only at high concentration (> or = 2 mM), while Mn2+ weakly activated peroxidase activity at concentration >3 mM but was active in the oxidoreductase oxidation at a low concentration (<1 mM). Fe2+-dependent peroxidase activity of dialysed IgGs was observed at 0.1-5 mM, but Fe2+ was completely inactive in the oxidoreductase reaction. Mg2+, Ca2+, Zn2+, Al2+ and especially Co2+ and Ni2+ were not able to activate dialysed IgGs, but slightly activated non-dialysed IgGs. The use of the combinations of Cu2+ + Mn2+, Cu2+ + Zn2+, Fe2+ + Mn2+, Fe2+ + Zn2+ led to a conversion of the biphasic curves to hyperbolic ones and in parallel to a significant increase in the activity as compared with Cu2+, Fe2+ or Mn2+ ions taken separately; the rates of the oxidation reactions, catalysed by non-dialysed and dialysed IgGs, became comparable. Mg2+, Co2+ and Ni2+ markedly activated the Cu2+-dependent oxidation reactions catalysed by dialysed IgGs, while Ca2+ inhibited these reactions. A possible role of the second metal in the oxidation reactions is discussed.     

Role of the capsule produced by Bacillus megaterium ATCC 19213 in the accumulation of metallic cations

A study was undertaken to determine if the capsule produced by Bacillus megaterium ATCC 19213 was capable of binding metallic ions. For non-toxic metallic ions, this was accomplished by determining the relative concentrations of Fe2+, Ca2+, Zn2+, Mg2+, and Mn2+ removed from a chemically defined medium by the normally capsulated parent strain and two mutants with much smaller capsules. For toxic metals, the rates of respiration of the parent strain and a small capsule mutant in the presence of Cu2+, Hg2+, and Ag1+ were compared. It was found that the parent strain accumulated more Ca2+, Mg2+, and Mn2+. Accumulation of Fe2+ and Zn2+ was similar for the parent strain and the small capsule mutants. Respiration of the parent strain was less inhibited by Cu2+, Hg2+, and Ag1+, indicating that these metals are also bound to the capsule.     

金属离子对嗜热菌BF80生长及苯酚降解的影响研究

探测了17种金属离子对嗜热菌BF80菌生长和降解苯酚的影响.结果表明:与对照相比,0.01%的Cu2 、Zn2 、CO2 、Ba2 、Hg2 、Ni2 、Al 0和Al3 对嗜热菌BF80有强抑制作用;Cr2 对嗜热菌BF80的苯酚降解特性有强抑制作用,而其生长量只受到一定的抑制作用;Sn2 、Fe2 、Fe3 和Pn2 对嗜热菌BF80的生长和苯酚降解有一定抑制作用,该作用随金属粒子浓度的增加而增大;低浓度Mn2 和Mo2 可以使其生长量增大且促进苯酚降解,但超过0.1%的浓度则抑制其生长;Ca2 和Mg2 可以加速嗜热菌BF80的生长和降解苯酚的速率,但对苯酚的最大降解率却几乎没有影响;Mo2 和Mn2 的复合作用使嗜热菌BF80的生长量更大,但是苯酚降解率却比分别单独添加Mo2 和Mn2 时低.     

Reduction of Mo6+ with elemental sulfur by Thiobacillus ferrooxidans.

In the presence of phosphate ions, molybdic ions (Mo6+) were reduced enzymatically with elemental sulfur by washed intact cells of Thiobacillus ferrooxidans to give molybdenum blue. The whole-cell activity that reduced Mo6+ was totally due to cellular sulfur:ferric ion oxidoreductase (SFORase) (T. Sugio, W. Mizunashi, K. Inagaki, and T. Tano, J. Bacteriol. 169:4916-4922, 1987). The activity of M06+ reduction with elemental sulfur was competitively inhibited by Fe3+, Cu2+, and Co2+. The Michaelis constant of SFORase for Mo6+ was 7.6 mM, and the inhibition constants for Fe3+, Cu2+, and Co2+ were 0.084, 0.015, and 0.17 mM, respectively, suggesting that SFORase can reduce not only Fe3+ and Mo6+ but also Cu2+ and Co2+ with elemental sulfur.     

金属离子对嗜热菌BF80生长及苯酚降解的影响研究

探测了17种金属离子对嗜热菌BF80菌生长和降解苯酚的影响。结果表明：与对照相比, 0.01%的Cu2+、Zn2+、Co2+、Ba2+、Hg2+、Ni2+、Ag+ 和Al3+对嗜热菌BF80有强抑制作用; Cr2+对嗜热菌BF80的苯酚降解特性有强抑制作用, 而其生长量只受到一定的抑制作用; Sn2+、Fe2+、Fe3+和Pn2+ 对嗜热菌BF80的生长和苯酚降解有一定抑制作用, 该作用随金属粒子浓度的增加而增大; 低浓度Mn2+ 和Mo2+可以使其生长量增大且促进苯酚降解, 但超过0.1%的浓度则抑制其生长; Ca2+ 和Mg2+可以加速嗜热菌BF80的生长和降解苯酚的速率, 但对苯酚的最大降解率却几乎没有影响; Mo2+ 和Mn2+的复合作用使嗜热菌BF80的生长量更大, 但是苯酚降解率却比分别单独添加Mo2+ 和Mn2+时低。     

Ferric and cupric reductase activities by iron-limited cells of the green alga Chlorella kessleri: quantification via oxygen electrode

The colorimetric Fe2+ indicators bathophenanthroline disulfonic acid (BPDS) and 3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine (FZ) are routinely used to assay for plasma membrane ferric reductase activity in iron-limited algal cells and also in roots from iron-limited plants. Ferric reductase assays using these colorimetric indicators must take into account the fact that Fe3+ chelators (e.g. ethylenediaminetetraacetic acid) can also in general bind Fe2+ and may therefore compete with the colorimetric Fe2+ indicators, leading to the potential for underestimation of the ferric reduction rate. Conversely, the presence of BPDS or FZ may also facilitate the reduction of Fe3+ chelates, potentially leading to overestimation of ferric reduction rates. Last, both BPDS and FZ have non-negligible affinities for Fe3+ in addition to their well-known affinities for Fe2+; this leads to potential difficulties in ascertaining whether free and/or chelated Fe3+ are potential substrates for the ferric reductase. Similar issues arise when assaying for cupric reductase activity using the colorimetric Cu+ indicator bathocuproinedisulfonic acid (BCDS). In this paper, we describe an oxygen-electrode-based assay (conducted in darkness) for both ferric and cupric reductase activities that does not use colorimetric indicators. Using this assay system, we show that the plasma membrane metal reductase activity of iron-limited cells of the green alga Chlorella kessleri reduced complexed Fe3+ (i.e. Fe3+ chelates) but did not reduce free (non-chelated) Fe3+, and also reduced free Cu2+ to Cu+, but did not reduce Cu2+ that was part of Cu2+ chelates. We suggest that the potential for reduction of free Fe3+ cannot be adequately assayed using colorimetric assays. As well, the BPDS-based assay system consistently yielded similar estimates of ferric reductase activity compared with the O2-electrode-based assays at relatively low Fe3+ concentration, but higher estimates at higher Fe3+ concentrations with chelators other than desferrioxamine mesylate. With respect to cupric reductase activity, the O2 electrode consistently provided much higher estimates; we suggest that this was as a result of Cu2+ chelation by BCDS leading to a large underestimation of the true cupric reduction rate. These results suggest that an O2-electrode-based metal reductase assay system has some specific advantages compared with the traditional colorimetric assay system, including especially the ability to discriminate between the reduction of free metal ions and chelated metal ions.     

A study of the molecular mechanism of DNA interaction with divalent metal ions

The interaction of DNA with divalent metal ions: Ba2+, Mg2+, Mn2+, Ni2+, Cu2+ in solutions at different ionic strengths mu was investigated. The combination of following methods: flow birefringence, viscometry, UV-spectroscopy and circular dichroism made possible to follow the state of the secondary and tertiary structure of the DNA molecule during its interaction with ions. The presence of divalent ions in solution affects the hydrodynamic properties of DNA only at low mu. At high mu the difference in the action of mono- and divalent ions disappears. The persistence length of DNA does not change during the experiment. It is shown that the Mg2+ and Ba2+ ions interact only with phosphate groups of DNA but Mn2+, Ni2+, Cu2+ ions interact also with the nitrogen bases of the macromolecule.     

Complexes of DNA with trivalent metal ions in presence of manganese ions

The interaction of DNA with Fe3+, Al3+, Co(NH3)6(3+) in a solution containing MnCl2 was studied. It was shown that there exists a competition for the binding sites between Mn2+ and Al3+, while the binding of Mn2+ to DNA does not depend on the presence of Fe3+ and Co(NH3)6(3+) in solution. We proposed that Fe3+ and Co(NH3)6(3+) ions prefer to bind to phosphates, and Al3+ ions are capable to bind to the nitrogen bases of DNA.     

金属离子对粪产碱杆菌C16的脱氮和亚硝酸盐积累的影响

【目的】研究不同金属离子对异养氨氧化细菌C16的生长和脱氮性能影响,探讨适于C16生长和脱氮的金属离子及其浓度。【方法】实验选用Mg2+、Mn2+、Fe2+、Cu2+、Zn2+5种金属离子,对C16的生长﹑脱氮性能﹑亚硝酸盐氮积累以及相关酶活性进行研究。【结果】Mg2+明显促进C16的生长和NH4+-N氧化速率;较高浓度Mn2+使得C16无法生长;原培养基中缺少Fe2+会抑制C16的生长和NH4+-N氧化速率;在原培养基中加入0.1 mmol/L的Cu2+对C16的生长和脱氮具有一定的促进作用,Cu2+使得培养基中基本无NO2--N和NH2OH的积累;不同浓度的Zn2+对C16的生长和氨氮去除有抑制作用。酶活实验结果显示,0.1 mmol/L Mg2+促进了羟胺氧化还原酶(HAO)的活性;0.1 mmol/L Cu2+促进了硝酸盐还原酶(Nar)和亚硝酸盐还原酶(Nir)的活性。【结论】Mg2+是C16生长和脱氮过程中的一种重要金属离子;加入Cu2+可避免过量亚硝酸盐积累。     

Inhibition of DNA-ethidium bromide intercalation due to free radical attack upon DNA

The fluorescent intercalation complex of ethidium bromide with DNA was used as a probe to demonstrate damage in the base-pair region of DNA, due to the action of superoxide radicals. The O.2- radical itself, generated by gamma-radiolysis of oxygenated aqueous Na-formate solutions, is rather ineffective with respect to impairment of DNA. Copper(II) ions, known to interact with DNA by coordinate binding at purines, enhance the damaging effect of O.2-. Addition of H2O2 to the DNA/Cu(II) system gives rise to further enhancement, so that DNA impairment by O.2- becomes comparable to that initiated by .OH radicals. These results suggest that the modified, Cu(II)-catalysed, Haber-Weiss process transforms O.2- into .OH radicals directly at the target molecule, DNA-Cu2+ + O.2-----DNA-Cu+ + O2 DNA-Cu+ + H2O2----DNA...OH + Cu2+ + OH- in a "site-specific" mechanism as proposed for other systems (Samuni et al. 1981; Aronovitch et al. 1984). Slow DNA decomposition also occurs without gamma-irradiation by autocatalysis of DNA/Cu(II)/H2O2 systems. In this context we observed that Cu(II) in the DNA-Cu2+ complex (unlike free Cu2+) is capable of oxidizing Fe(II) to Fe(III), thus the redox potential of the Cu2+/Cu+ couple appears to be higher than that of the Fe3+/Fe2+ couple when the ions are complexed with DNA. Metal-catalysed DNA damage by O.2- also occurs with Fe(III), but not with Ag(I) or Cd(II) ions. It was also observed that Cu(II) ions (but neither Ag(I) nor Cd(II] efficiently quench the fluorescence of the intercalation complex of ethidium bromide with DNA.     

Structural role of zinc ions bound to postsynaptic densities

Postsynaptic densities (PSDs) isolated from porcine cerebral cortices are large aggregates consisting of more than 30 different proteins. Inductively coupled plasma-mass spectrometric analyses revealed that isolated PSDs contained zinc at a concentration of 4.1 nmol per mg protein. Treatment with 8 m urea lead to dissociation of the PSDs into small components and, concomitantly, depletion of most of their bound zinc. After removal of the urea by dialysis, urea-dissociated PSD proteins did not reassemble into aggregates by themselves. Adding ZnCl2 to urea-treated PSD samples resulted in the assembly of urea-dissociated proteins into large aggregates with morphology and protein composition closely resembling those of the original PSDs. Mg2+, Ca2+, Co2+, Cd2+, Cu2+, Mn2+, Fe3+, K+ and Na+ ions at higher concentrations also induced the aggregation of urea-dissociated PSD protein. The structures of the K+-, Na+-, Mg2+- and Ca2+-induced aggregates were distinct from that of the original PSDs. Our results indicate that the structure of the PSD could be disassembled and reassembled under in vitro conditions. They further suggest that Zn2+ ions, by binding to certain zinc-binding proteins, play an important role in the formation and maintenance of the structure of the PSD.     

DNA structural transitions induced by divalent metal ions in aqueous solutions

Using methods of IR spectroscopy, light scattering, gel-electrophoresis DNA structural transitions are studied under the action of Cu2+, Zn2+, Mn2+, Ca2+ and Mg2+ ions in aqueous solution. Cu2+, Zn2+, Mn2+ and Ca2+ ions bind both to DNA phosphate groups and bases while Mg2+ ions-only to phosphate groups of DNA. Upon interaction with divalent metal ions studied (except for Mg2+ ions) DNA undergoes structural transition into a compact form. DNA compaction is characterized by a drastic decrease in the volume occupied by DNA molecules with reversible formation of DNA dense particles of well-defined finite size and ordered morphology. The DNA secondary structure in condensed particles corresponds to the B-form family. The mechanism of DNA compaction under Mt2+ ion action is not dominated by electrostatics. The effectiveness of the divalent metal ions studied to induce DNA compaction correlates with the affinity of these ions for DNA nucleic bases: Cu2+>Zn2+>Mn2+>Ca2+>Mg2+. Mt2+ ion interaction with DNA bases (or Mt2+ chelation with a base and an oxygen of a phosphate group) may be responsible for DNA compaction. Mt2+ ion interaction with DNA bases can destabilize DNA causing bends and reducing its persistent length that will facilitate DNA compaction.