Effect of cAMP-elevating drugs on Ca2+ efflux and actin polymerization in peritoneal macrophages stimulated with N-formyl chemotactic peptide

To investigate intracellular cAMP inhibitory mechanisms related to migration of guinea-pig peritoneal macrophages, we examined the effects of cAMP-elevating drugs on the Ca²⁺ efflux and actin polymerization in macrophages stimulated with fMet-Leu-Phe, a chemotactic peptide. The stimulation with 1·10^?8 M fMet-Leu-Phe enhanced the Ca²⁺ efflux, and induced actin polymerization. Dibutyryl cAMP, theophylline and papaverine, which continuously increased the levels of intracellular cAMP, inhibited the enhancement of Ca²⁺ efflux and induction of actin polymerization by fMet-Leu-Phe. On the other hand, isoproterenol, which transiently increased the cAMP level, inhibited only the early phase of Ca²⁺ efflux and not the actin polymerization. As additions of both cAMP and cAMP-dependent protein kinase did not modify the Ca²⁺ uptake of phagocytic vesicles, the inhibition of Ca²⁺ efflux by these drugs may be due to the inhibition of the Ca²⁺ release from the intracellular store site(s). The cAMP-elevating drugs increased the monomeric actin content without change in the total actin content, indicating an induction of the depolymerization of filamentous actin. From these findings, we conclude that the inhibition of macrophage migration induced by cAMP may be due to the inhibition of both the increase of intracellular Ca²⁺ concentration and actin polymerization. Furthermore, the intracellular levels of cAMP probably play a role in regulating actin states in the macrophages.     

Selective binding of Ni2+ and Cu2+ metal ions with naphthazarin esters isolated from Arnebia euchroma

Naphthazarin esters (C1–C4) isolated from the roots of Arnebia euchroma are found as skilled dual chemosensors for Ni²⁺ and Cu²⁺ among Pb²⁺, Na²⁺, K²⁺, Hg²⁺, Mg²⁺, and Ca²⁺ metal ions. C1–C4 esters exhibited a red shift of 54 nm with Ni²⁺ and 30 nm with Cu²⁺ metal ions in absorption. There is a formation of red-shifted bands between 517 and 613 nm in the absorption spectrum of C1–C4 sensors on binding with Ni²⁺ and Cu²⁺ ions. The addition of Ni²⁺ and Cu²⁺ ions to sensors C1–C4 stimulates a remarkable color change from reddish pink to purple and light blue, respectively. These color changes can be identified with the naked eye. The significant downfield shifts of CO and OH peaks in nuclear magnetic resonance (NMR) spectrum confirm the chelation as binding mechanism. With ultraviolet–visble and NMR studies, it is found that C1–C4 esters possessed notable selectivity and sensitivity toward Ni²⁺ and Cu²⁺ over other metal ions.     

Inhibition of Mn2+-induced error-prone DNA synthesis with Cd2+ and Zn2+

Bivalent metal cations are key components in the reaction of DNA synthesis. They are necessary for all DNA polymerases, being involved as cofactors in catalytic mechanisms of nucleotide polymerization. It is also known that in the presence of Mn²⁺ the accuracy of DNA synthesis is considerably decreased. The findings of this work show that Cd²⁺ and Zn²⁺ selectively inhibit the Mn²⁺-induced error-prone DNA polymerase activity in extracts of cells from human and mouse tissues. Moreover, these cations in low concentrations also can efficiently inhibit the activity of homogeneous preparations of DNA polymerase iota (Pol ?), which is mainly responsible for the Mn²⁺-induced error-prone DNA polymerase activity in cell extracts. Using a primary culture of granular cells from postnatal rat cerebellum, we show that low concentrations of Cd²⁺ significantly increase cell survival in the presence of toxic Mn²⁺ doses. Thus, we have shown that in some cases low concentrations of Cd²⁺ can display a positive influence on cells, whereas it is widely acknowledged that this metal is not a necessary microelement and is toxic for organisms.     

A key role for reverse Na+/Ca2+ exchange influenced by the actin cytoskeleton in store-operated Ca2+ entry in human platelets: Evidence against the de novo conformational coupling hypothesis

We have previously demonstrated a role for the reorganization of the actin cytoskeleton in store-operated calcium entry (SOCE) in human platelets and interpreted this as evidence for a de novo conformational coupling step in SOCE activation involving the type II IP₃ receptor and the platelet hTRPC1-containing store-operated channel (SOC). Here, we present evidence challenging this model. The actin polymerization inhibitors cytochalasin D or latrunculin A significantly reduced Ca²⁺ but not Mn²⁺ or Na⁺ entry into thapsigargin (TG)-treated platelets. Jasplakinolide, which induces actin polymerization, also inhibited Ca²⁺ but not Mn²⁺ or Na⁺ entry. However, an anti-hTRPC1 antibody inhibited TG-evoked entry of all three cations, indicating that they all permeate an hTRPC1-containing store-operated channel (SOC). These results indicate that the reorganization of the actin cytoskeleton is not involved in SOC activation. The inhibitors of the Na⁺/Ca²⁺ exchanger (NCX), KB-R7943 or SN-6, caused a dose-dependent inhibition of Ca²⁺ but not Mn²⁺ or Na⁺ entry into TG-treated platelets. The effects of the NCX inhibitors were not additive with those of actin polymerization inhibitors, suggesting a common point of action. These results indicate a role for two Ca²⁺ permeable pathways activated following Ca²⁺ store depletion in human platelets: A Ca²⁺-permeable, hTRPC1-containing SOC and reverse Na⁺/Ca²⁺ exchange, which is activated following Na⁺ entry through the SOC and requires a functional actin cytoskeleton.     

Isolation and characterization of a Ca2+-activated actin-modulating protein from obliquely striated muscle

Summary An actin-modulating protein has been isolated from the obliquely striated body wall muscle of the earthwormLumbricus terrestris. The isolation procedure included extraction in the absence of Ca²⁺ with subsequent ammonium sulfate fractionation followed by ion exchange chromatography and gel filtration. The purified modulator preparation appears on SDS-PAGE as a doublet of bands with molecular weights of 43 and 45 kDa. Both separately isolated components exhibit the same actin-modulating properties and therefore probably represent two isoforms. Substoichiometric amounts of modulator sever actin filaments and effectively promote nucleation of actin polymerization, which results in the formation of short actin filaments. Both effets are completely dependent on the presence of Ca²⁺ and activation of the modulator occurs in a narrow range of free Ca²⁺ concentrations around 10^–6 mmol l^–1. The modulator increases the critical concentration for actin polymerization, indicating that it binds to the fast polymerizing end of the actin filaments. The modulator forms a stoichiometric complex with two actin molecules whereby its ability to sever actin filaments is lost.The properties of the earthworm actin modulator are discussed in comparison with similar actinassociated proteins.Abbreviations BSA bovine serum albumin - DTE dithioerythritol - EWAM earthworm actin modulator - IEF isoelectric focusing - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulfonyl fluoride - SDS sodium dodecyl sulfate Dedicated to Professor Dr. K.-E. Wohlfarth-Bottermann, Bonn, on the occasion of his 65th birthday     

Ca2+ attenuates nucleation activity of leiomodin

A transient increase in Ca²⁺ concentration in sarcomeres is essential for their proper function. Ca²⁺ drives striated muscle contraction via binding to the troponin complex of the thin filament to activate its interaction with the myosin thick filament. In addition to the troponin complex, the myosin essential light chain and myosin‐binding protein C were also found to be Ca²⁺ sensitive. However, the effects of Ca²⁺ on the function of the tropomodulin family proteins involved in regulating thin filament formation have not yet been studied. Leiomodin, a member of the tropomodulin family, is an actin nucleator and thin filament elongator. Using pyrene‐actin polymerization assay and transmission electron microscopy, we show that the actin nucleation activity of leiomodin is attenuated by Ca²⁺. Using circular dichroism and nuclear magnetic resonance spectroscopy, we demonstrate that the mostly disordered, negatively charged region of leiomodin located between its first two actin‐binding sites binds Ca²⁺. We propose that Ca²⁺ binding to leiomodin results in the attenuation of its nucleation activity. Our data provide further evidence regarding the role of Ca²⁺ as an ultimate regulator of the ensemble of sarcomeric proteins essential for muscle function.Summary StatementCa²⁺ fluctuations in striated muscle sarcomeres modulate contractile activity via binding to several distinct families of sarcomeric proteins. The effects of Ca²⁺ on the activity of leiomodin—an actin nucleator and thin filament length regulator—have remained unknown. In this study, we demonstrate that Ca²⁺ binds directly to leiomodin and attenuates its actin nucleating activity. Our data emphasizes the ultimate role of Ca²⁺ in the regulation of the sarcomeric protein interactions.     

Purification and characteristics of Ca2+,Mg2+- and Ca2+,Mn2+-dependent and acid DNases from spermatozoa of the sea urchin Strongylocentrotus intermedius

Ca²⁺,Mg²⁺- and Ca²⁺,Mn²⁺-dependent and acid DNases were isolated from spermatozoa of the sea urchin Strongylocentrotus intermedius. The enzymes have been purified by successive chromatography on DEAE-cellulose, phenyl-Sepharose, Source 15Q, and by gel filtration, and the principal physicochemical and enzymatic properties of the purified enzymes were determined. Ca²⁺,Mg²⁺-dependent DNase (Ca,Mg-DNase) is a nuclear protein with molecular mass of 63 kD as the native form and its activity optimum is at pH 7.5. The enzyme activity in the presence of bivalent metal ions decreases in the series (Ca²⁺ + Mg²⁺) > Mn²⁺ = (Ca²⁺ + Mn²⁺) > (Mg²⁺ + EGTA) > Ca²⁺. Ca,Mg-DNase retains its maximal activity in sea water and is not inhibited by G-actin and N-ethylmaleimide, whereas Zn²⁺ inhibits the enzyme. The endogenous Ca,Mg-DNase is responsible for the internucleosomal cleavage of chromosomal DNA of spermatozoa. Ca²⁺,Mn²⁺-dependent DNase (Ca,Mn-DNase) has molecular mass of 25 kD as the native form and the activity optimum at pH 8.5. The enzyme activity in the presence of bivalent metal ions decreases in the series (Ca²⁺ + Mn²⁺) > (Ca²⁺ + Mg²⁺) > Mn²⁺ > (Mg²⁺ + EGTA). In seawater the enzyme is inactive. Zinc ions inhibit Ca,Mn-DNase. Acid DNase of spermatozoa (A-DNase) is not a nuclear protein, it has molecular mass of 37 kD as a native form and the activity optimum at pH 5.5, it is not activated by bivalent metal ions, and it is inhibited by N-ethylmaleimide and iodoacetic acid. Mechanisms of the endonuclease cleavage of double-stranded DNA have been established for the three enzymes. The possible involvement of DNases from sea urchin spermatozoa in programmed cell death is discussed.     

Actin assembly by cadmium ions

Cadmium is a highly toxic metal entering cells by a variety of mechanisms. Its toxic action is far from being completely understood, although specific interaction with the cellular calcium metabolism has been indicated. Metal ions that influence intracellular Ca²⁺ concentrations or compete with Ca²⁺ for protein binding sites may exert an effect on actin filaments, whose assembly and disassembly are both regulated by a number of calcium-dependent factors. Cadmium is such a metal. Much evidence demonstrates that cadmium interferes with the dynamics of actin filaments in various types of cells. Here we show that, at high (0.8–1.0 mM) concentrations, CdCl₂ causes actin denaturation. At such Cd²⁺ concentrations, actin precipitates (really actin, as shown by SDS-PAGE, see Fig. 1B) in the form of irregular, disordered clots, clearly appreciable by electron microscopy. Denaturation seems to be reversible since, after Cd²⁺ removal by dialysis, the polymerizability of sedimented actin is restored almost completely. On the other hand, at concentrations ranging from 0.25 to 0.6 mM, CdCl₂ is more effective as an actin polymerizing agent than both MgCl₂ and CaCl₂. The Cd-related increase in the actin assembly rate is ascribable to an enhanced nucleation rather than to an increased monomer addition to filament growing ends. The latter, in contrast, appears quite slow. Critical concentration measurements revealed that the extent of polymerization of both Mg- and Cd-assembled actin are very close (C_c ranges from 0.25 to 0.5 μM), while Ca-polymerized actin shows a polymerization extent markedly lower (C_c=4.0 μM). By both the fluorescent Ca²⁺ chelator Quin-2 assay and limited proteolysis of actin by trypsin and α-chymotrypsin, the real substitution of G-actin-bound Ca²⁺ by Cd²⁺ has been appreciated. The increase in Quin-2 fluorescence after addition of excess CdCl₂ indicates that, in our experimental conditions, Ca²⁺ tightly-bound to actin is partially (60–70%) replaced by Cd²⁺, forming Cd-actin. Electrophoretic patterns after limited proteolysis reveal that the trypsin cleavage sites in the segment 61–69 of the actin polypeptide chain are less accessible in Cd-actin than in Ca-actin, although the cation-dependent effect is less pronounced in Cd-actin than in Mg-actin. Our results are consistent with some of the consequences on microfilament organization observed in Cd²⁺-treated cells; however, considering the positive effect of Cd²⁺ on actin polymerization in solution we have noticed that this was never observed in vivo. A different indirect effect of Cd²⁺ on some cellular event(s) influencing cytoplasmic actin polymerization appears to be reasonable. © 1997 Elsevier Science B.V. All rights reserved.     

Studies of biosorption of Pb2+, Cd2+ and Cu2+ from aqueous solutions using Adansonia digitata root powders

The potentials of Adansonia digitata root powders (ADRP) for adsorption of Pb²⁺, Cd²⁺ and Cu²⁺ from aqueous solutions was investigated. Physico-chemical analysis of the adsorbent (ADRP) shows that hydroxyl, carbonyl and amino groups were predominant on the surface of the adsorbent. Scanning Electron Microscope (SEM) image revealed its high porosity and irregular pores in the adsorbent while the Energy Dispersive X-ray Spectrum showed the major element with 53.0% Nitrogen, 23.8% carbon, 9.1% calcium, 7.5% potassium and 6.6% magnesium present. The found optimal conditions were: initial concentration of the metal ions = 0.5 mg/L, pH = 5, contact time = 90 min, adsorbent dose = 0.4 g and particle size = 32 µm. Freundlich isotherm showed good fit for the adsorption of Pb²⁺, Cd²⁺ and Cu²⁺. Dubinin-Radushkevich isotherm revealed that the adsorption processes were physisorption Cd(II) and Cu(II) but chemisorption with respect to Pb(II) ions. The kinetics and thermodynamic studies showed that Pseudo-second order and chemisorptions provided the best fit to the experimental data of Pb (II) ions only. Batch desorption result show that desorption in the acidic media for the metal ions were more rapid and over 90% of the metal ions were recovered from the biomass.     

Co2+ and Mn2+ uptake by crab nerve fibers in resting state and potassium depolarization

Transition metal ions, Mn²⁺ and Co²⁺, are incorporated into nerve fibers when they are applied externally. For nerve fibers in the resting state, however, extracellular and intracellular water may be distinguished by applying transition metal ions externally. NMR spectra of water protons from nerve fibers in high potassium media, which contain transition metal ions, consist of three or more components, reflecting a complex distribution of these ions around the nerve membranes. In the case of Co²⁺, three components may be identified.     

Adsorption of Ni2+ and Cu2+ using Bio-Mineral: Adsorption Isotherms and Mechanisms

Heavy metal pollution has become one of the most serious environmental pollution problems. This study aimed to determine the adsorption and desorption characteristics of Ni²⁺ and Cu²⁺ by bio-mineral which was induced by Bacillus subtilis, and to explore the effect of pH on adsorption characteristics. The results showed that the Langmuir model gave a better fit to the experimental data than the Freundlich model, which demonstrated the adsorption was of a single-molecule layer form. The maximum adsorption capacities of the bio-mineral for Ni²⁺ and Cu²⁺ were determined as 67.114 mg/g and 69.930 mg/g, respectively. The desorption rates of Ni²⁺ and Cu²⁺ were very low, especially for Ni²⁺ which was almost 0. Besides, the bio-mineral maintained high adsorption capability for metals ions within a wide pH range (pH ≥ 3). It did not show any new phases after adsorption of Ni²⁺ and Cu²⁺ tested by FTIR, indicating that the bio-mineral and heavy metal ions might mainly physically be adsorbed. The bio-mineral has a larger internal and external specific surface area, pore volume and colloidal properties which are beneficial for the adsorption of metals ions, but shows limits in desorption. This study provides a theoretical basis for the utilization of bio-mineral and opens a new perspective for the remediation of heavy metals pollution.     

Interaction of Aplysia brasiliana Myoglobin with Mn2+ and Cu2+ ions

Myoglobin of Aplysia brasiliana (MbApB) has been recently purified and characterized and it was shown that the amino acid content is quite different from other myoglobins. A large number of aromatic residues was observed together with the existence of a unique histidine at the proximal heme position. Because of the numerous differences in the amino acid sequence between MbApB and whale myoglobin, it was interesting to investigate the interaction of metal ions like Cu²⁺ and Mn²⁺ with MbApB. In the present work Cu²⁺ complexes with Met-MbApB were studied and show a pH transition between different forms of coordination as revealed by EPR measurements. At high pH the EPR spectrum shows the coordination of the metal to at least four nitrogens from ϵ-NH₃ lysine residues. At lower pH in the range 6.0–9.0 the copper binding site shows a pK change of some of the residues involved in metal coordination. Addition of one equivalent Cu²⁺ per protein does not alter the iron EPR signal. The manganese ion has one binding site in MbApB and a binding constant K_a = ( 11.5 ± 0.8) 10³M⁻¹. The binding of Cu²⁺ to MbApB is stronger than Mn²⁺, K_a^Cu2+ >K_a^Mn2+.     

R.KpnI, an HNH superfamily REase, exhibits differential discrimination at non-canonical sequences in the presence of Ca2+ and Mg2+

KpnI REase recognizes palindromic sequence, GGTAC↓C, and forms complex in the absence of divalent metal ions, but requires the ions for DNA cleavage. Unlike most other REases, R.KpnI shows promiscuous DNA cleavage in the presence of Mg²⁺. Surprisingly, Ca²⁺ suppresses the Mg²⁺-mediated promiscuous activity and induces high fidelity cleavage. To further analyze these unique features of the enzyme, we have carried out DNA binding and kinetic analysis. The metal ions which exhibit disparate pattern of DNA cleavage have no role in DNA recognition. The enzyme binds to both canonical and non-canonical DNA with comparable affinity irrespective of the metal ions used. Further, Ca²⁺-imparted exquisite specificity of the enzyme is at the level of DNA cleavage and not at the binding step. With the canonical oligonucleotides, the cleavage rate of the enzyme was comparable for both Mg²⁺- and Mn²⁺-mediated reactions and was about three times slower with Ca²⁺. The enzyme discriminates non-canonical sequences poorly from the canonical sequence in Mg²⁺-mediated reactions unlike any other Type II REases, accounting for the promiscuous behavior. R.KpnI, thus displays properties akin to that of typical Type II REases and also endonucleases with degenerate specificity in its DNA recognition and cleavage properties.     

Overexpression of AtMHX in tobacco causes increased sensitivity to Mg<Superscript>2+</Superscript>, Zn<Superscript>2+</Superscript>, and Cd<Superscript>2+</Superscript> ions,induction of V-ATPase expression,and a reduction in plant size

AtMHX is a vacuolar transporter encoded by a single gene in Arabidopsis. Electrophysiological analysis showed that it exchanges protons with Mg²⁺, Zn²⁺, and Fe²⁺ ions. The physiological impact of AtMHX was examined so far only in tissue-culture grown seedlings of tobacco plants overexpressing this transporter. Here we investigated the impact of AtMHX on growth, response to different metals, and metal accumulation of mature tobacco plants, as well as Arabidopsis plants in which we overexpressed this transporter. The analyses were carried out in hydroponic growth-systems, in which the mineral composition could be effectively controlled, and the metal content of roots could be examined. Transformed tobacco plants showed necrotic lesions and apical burnings upon growth with increased levels of Mg²⁺, Zn²⁺, and Cd²⁺ ions. This suggested that AtMHX can carry in planta not only Mg²⁺ and Zn²⁺ ions, as previously deduced based on observations in tissue-culture, but also Cd²⁺ ions. Transformed plants of both tobacco and Arabidopsis showed a reduction in plant size. However, the overall response of Arabidopsis to AtMHX overexpression was minor. No change was detected in the mineral content of any organ of the transgenic tobacco or Arabidopsis plants. The necrotic lesions in tobacco resembled those seen in plants with perturbed proton balancing, raising the assumption that AtMHX can affect the proton homeostasis of cells. In agreement with this assumption, the transformed tobacco plants had increased expression and activity of the vacuolar H⁺-ATPase. The relative significance of AtMHX for metal and proton homeostasis still has to be elucidated.     

Spectroscopic Analysis of the Cu<Superscript>2+</Superscript>-Induced Fluorescence Quenching of Fluorescent Proteins AmCyan and mOrange2

Fluorescent proteins show fluorescence quenching by specific metal ions, which can be applied towards metal biosensing applications. In order to develop metal-biosensor, we performed spectroscopic analysis of the fluorescence quenching of fluorescent protein AmCyan and mOrange2 by various metal ions. The fluorescence intensity of AmCyan was reduced to 48.54% by Co²⁺ and 67.77% by Zn²⁺; Cu²⁺ reduced the fluorescence emission of AmCyan to 19.30% of its maximum. The fluorescence intensity of mOrange2 was quenched by only Cu²⁺, to 11.48% of its maximum. When analyzed by Langmuir equation, dissociation constants for AmCyan and mOrange2 were 56.10 and 21.46 µM, respectively. The Cu²⁺ quenching of AmCyan and mOrange2 were reversible upon treatment with the metal chelator EDTA, indicating that the metal ions were located on the protein surface. Their model structures suggest that AmCyan and mOrange2 have novel metal-binding sites.     

Genetic engineering of bacteria and their potential for Hg2+ bioremediation

Ion exchange or biosorptive processes for metalremoval generally lack specificity in metal bindingand are sensitive to ambient conditions, e.g. pH,ionic strength and the presence of metal chelators. Inthis study, cells of a genetically engineered Escherichia coli strain, JM109, which expressesmetallothionein and a Hg²⁺ transport system afterinduction were evaluated for their selectivity forHg²⁺ accumulation in the presence of sodium,magnesium, or cadmium ions and their sensitivity to pHor the presence of metal chelators during Hg²⁺bioaccumulation. The genetically engineered E.coli cells in suspension accumulated Hg²⁺effectively at low concentrations (0-20 µM) overa broad range of pH (3 to 11). The presence of 400 mMsodium chloride, 200 mM magnesium chloride, or100 µM cadmium ions did not have a significanteffect on the bioaccumulation of 5 µm Hg²⁺,indicating that this process is not sensitive to highionic strength and is highly selective against sodium,magnesium, or cadmium ions. Metal chelators usuallyinterfere with ion exchange or biosorptive processes.However, two common metal chelators, EDTA and citrate,had no significant effect on Hg²⁺ bioaccumulationby the genetically engineered strain. These resultssuggest that this E. coli strain could be usedfor selective removal of Hg²⁺ from waste water orfrom contaminated solutions which are resistant tocommon treatments. A second potential applicationwould be to remove Hg²⁺ from Hg²⁺-contaminated soil, sediment, or particulates bywashing them with a Hg²⁺ chelator andregenerating the chelator by passing the solutionthrough a reactor containing the strain.     

The binding of Mn2+ and ADP to myosin

The metal ion requirement of myosin-ADP binding was investigated by use of Mn²⁺. Mn²⁺ binds to two sets of noninteracting sites on myosin which are characterized by affinity constants of 10⁶ and 10³, M⁻¹ at 0.016 M KCl concentration. The maximum number of sites is 2 for the high affinity and 20–25 for the low affinity set. Binding of Mn²⁺ to the high affinity sites increases the affinity of ADP binding to myosin. F-actin inhibits ADP binding (Kiely, B., and Martonosi, A., Biochim. Biophys. Acta 172: 158–170 [1969]), but even at F-actin concentrations much higher than that required to saturate the actin binding sites of myosin or its proteolytic fragments, significant ADP binding remained. The actin insensitive portion of ADP binding was inhibited by 10⁻⁴ M inorganic pyrophosphate or ATP. The results are discussed on the basis of a model in which actin and ADP bind to myosin at distinct but interacting sites.     

Cr3+和Cd2+对普通小球藻生长及抗氧化酶活性的影响

[目的] 为探究重金属对淡水绿藻生长的影响。[方法] 选取对水质检测具有明显指示作用的普通小球藻（Chlorella vulgaris）为实验材料,CdCl₂·2H₂O和CrCl₃·7H₂O提供重金属离子,探究不同浓度Cr³⁺和Cd²⁺在单一和复合胁迫下对藻细胞浓度、叶绿素a及相关抗氧化酶活性的影响。[结果] 随着Cr³⁺和Cd²⁺浓度不断增加,藻细胞浓度呈先增长后下降趋势;叶绿素a含量呈现先下降后升高再下降的现象,浓度为1 mg/L的单一和复合胁迫下有最大值,且毒性作用表现为Cr³⁺ < Cd²⁺ < Cr³⁺+Cd²⁺;与藻细胞膜相关的丙二醛（MDA）和过氧化氢（H₂O₂）含量随着重金属离子浓度的增大而增长;重金属离子浓度低于10 mg/L时对藻细胞内抗氧化酶系统中的超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和过氧化物酶（POD）表现为促进作用,而大于10 mg/L时具有抑制作用。[结论] 结果表明在单一或复合重金属胁迫下,普通小球藻会充分调动与抗逆性相关的酶来维持自身的正常生长。     

Ni2+-uptake inPseudomonas putida strain S4: a possible role of Mg2+-uptake pump

Essential metal ion homeostasis is based on regulated uptake of metal ions, both during its scarcity and abundance.Pseudomonas putida strain S4, a multimetal resistant bacterium, was employed to investigate Ni²⁺ entry into cells. It was observed that Mg²⁺ regulates the entry of Ni²⁺ and by this plays a protective role to minimize Ni²⁺ toxicity in this strain. This protection was evident in both growth as well as viability. Intracellular accumulation of Ni²⁺ varied in accordance with Mg²⁺ concentrations in the medium. It was hypothesized that Ni²⁺ enters the cell using a broad Mg²⁺ pump, i.e. the CorA system, as the CorA inhibitor, i.e. Co(III) Hex, also inhibits Ni²⁺ uptake. This led to the inference that Mg²⁺-based protection was basically due to competitive inhibition of Ni²⁺ uptake. We also show that Zn²⁺ can further regulate the entry of Ni²⁺     

Resistance and bioaccumulation of Cd2+, Cu2+, Co2+ and Mn2+ by thermophilic bacteria, Geobacillus thermantarcticus and Anoxybacillus amylolyticus

In this study, bioaccumulation and heavy metal resistance of Cd²⁺, Cu²⁺, Co²⁺ and Mn²⁺ ions by thermophilic Geobacillus thermantarcticus and Anoxybacillus amylolyticus was investigated. The bacteria, in an order with respect to metal resistance from the most resistant to the most sensitive, was found to be Mn²⁺ > Co²⁺ > Cu²⁺ > Cd²⁺ for both G. thermantarcticus and A. amylolyticus. It was determined that the highest metal bioaccumulation was performed by A. amylolyticus in Mn²⁺ (28,566 μg/g dry weight), and the lowest metal bioaccumulation was performed by A. amylolyticus in Co²⁺ (327.3 μg/g dry weight). The highest Cd²⁺ capacities of dried cell membrane was found to be 36.07 and 39.55 mg/g membrane for G. thermantarticus and A. amylolyticus, respectively, and the highest Cd²⁺ capacities of wet cell membrane was found to be 14.36 and 12.39 mg/g membrane for G. thermantarcticus and A. amylolyticus, respectively.