钙离子和镁离子浓度变化对磷脂酰乙醇胺-磷脂酰甘油双分子层膜的影响

Ca²⁺ and Mg²⁺ ions are the main divalent cations in living cells and play vital roles in the structure and function of biological membranes. To date, the differences in the effects of these two ions on the Escherichia coli (E. coli) inner membrane at various concentrations remain unknown. Here, the effects of Ca²⁺ and Mg²⁺ ions on a mixed lipid bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) in a 3 : 1 ratio (mol/mol), which mimics the E. coli inner membrane, were quantitatively differentiated at different concentrations by dynamic light scattering (DLS), zeta potential measurements and all-atom molecular dynamics (AA-MD) simulations. The DLS results demonstrated that the POPE/POPG liposomes were homogeneous and monodisperse in solutions with Ca²⁺ or Mg²⁺ ion concentrations of 0 and 1 mmol∙L^-1. As the Ca²⁺ or Mg²⁺ ion concentration was increased to 5-100 mmol∙L^-1, lipid aggregation or the fusion of unilamellar liposomes occurred in the ion solutions. The zeta potential measurements showed that both the Ca²⁺ and Mg²⁺ ions had overcharging effects on the negatively charged POPE/POPG liposomes. The AA-MD simulation results indicated that the Ca²⁺ ions irreversibly adsorbed on the membranes when the simulation time was longer than 100 ns, while the Mg²⁺ ions were observed to dynamically adsorb on and desorb from the membranes at various concentrations. These results are consistent with the DLS and zeta potential experiments. The average numbers of Ca²⁺ and Mg²⁺ ions in the first coordination shell of the oxygen atoms of the phosphate, carbonyl and hydroxyl groups of POPE and POPG (i.e., the first coordination numbers) in the pure membrane and membranes containing 5 and 100 mmol∙L^-1 ions were calculated from the radial distribution functions. The results indicated that the primary binding site of these two ions on POPE and POPG at the concentrations studied was the negatively charged phosphate group. Thus, these results might explain the overcharging effects of both the Ca²⁺ and Mg²⁺ ions on the POPE/POPG liposomes. Moreover, as the Ca²⁺ concentration increased, the area per lipid of the lipid bilayers decreased, and the membrane thickness increased, while the Mg²⁺ ions had negligible effects on these membrane parameters. In addition, these ions had different effects on the orientation of the lipid head groups. These simulation results may be used to provide the possible explanations for the differences between Ca²⁺ and Mg²⁺ ions in DLS and zeta potential measurements at the atomic level. The experimental results and MD simulations provide insight into various biological processes regulated by divalent cations, such as membrane fusion.     

Molecular dynamics study of the influence of calcium ions on the conformation of gelsolin S2 domain

Gelsolin is an actin-severing protein whose action is promoted by Ca²⁺ ions and inhibited by binding to lipid phosphoinositides incorporated in the inner leaflet of the plasma membrane inner lipid bilayer. In this study, we carried out molecular dynamics (MD) simulations to investigate the influence of calcium cations on the conformation of gelsolin S2 domain. First, gelsolin S2 domain taken from the crystal structure of apo-gelsolin (PDB code: 1D0N) was subjected to three 1100 ps MD simulations in a periodic water box with the 5.0 force field at T=298 K. In the first simulation (S2_Ca²⁺) excess concentration of Ca²⁺ was applied, in the second one (S2_phys) the concentration of Ca²⁺ ions was physiological and in the third one (S2_w) no Ca²⁺ ions were added. The results of MD simulations showed high conformational flexibility of the N-terminal part of the S2 domain. S2_w deviated from the starting structure considerably more that S2_phys and S2_Ca²⁺ suggesting that Ca²⁺ ions stabilize the conformation of the S2 domain of gelsolin.     

Ca2+诱导的淀粉液化芽孢杆菌α-淀粉酶分子的生物活性和结构变化

在研究Ca²⁺对淀粉液化芽孢杆菌α-淀粉酶分子生物活性影响的基础上, 采用荧光光谱法和傅里叶变换红外光谱法研究了Ca²⁺诱导的酶分子结构变化. 结果表明, 当溶液中Ca²⁺浓度低于25.0 mmol/L时, Ca²⁺对酶分子具有激活作用; 而当Ca²⁺浓度高于25.0 mmol/L时, Ca²⁺对酶分子的生物活性具有抑制作用. 在Ca²⁺诱导的淀粉液化芽孢杆菌α-淀粉酶分子结构变化过程中, 酶分子仅发生二级结构的变化, 并不涉及其三级结构. 当Ca²⁺对酶分子具有激活作用时, 酶分子中的无规卷曲结构及β-折叠结构的含量下降, 而α-螺旋结构及β-转角结构的含量上升; 而当Ca²⁺对酶分子生物活性具有抑制作用时, 酶分子中的α-螺旋结构及β-转角结构的含量下降, 而无规卷曲结构及β-折叠结构的含量上升.     

Supported lipid bilayer formation by the giant vesicle fusion induced by vesicle–surface electrostatic attractive interaction

The effect of the electrostatic attractive force between giant unilamellar vesicles (GUVs) and the SiO₂ surface on the formation of a Ca²⁺-free supported lipid bilayer (SLB) was investigated by atomic force microscopy and fluorescence microscopy. When negatively charged GUVs were incubated for 1 h without Ca²⁺, the surface coverage of lipid bilayer was <1% on the SiO₂ surface. In contrast, a high coverage was obtained without addition of Ca²⁺ on the positively charged surface modified by aminopropyldimethylethoxysilane, and the coverage of SLBs decreased with increasing KCl concentrations. The thickness of the water layer under SLB was reduced by modification of APS.     

LIPID PEROXIDATION AND OTHER MEMBRANE DAMAGE PRODUCED IN Escherichia coli K1060 BY NEAR-UV RADIATION AND DEUTERIUM OXIDE

Abstract— With accumulating evidence that the membrane is an important site for near-UV inactivating events, we have investigated the effects of near-UV radiation on the unsaturated fatty acid auxotroph E. coli K1060 following incorporation into the membrane phospholipids of fatty acids with varying degrees of unsaturation. Sensitivity, lipid peroxidation and membrane damage, as determined by ⁸⁶Rb⁺ leakage, have been found to increase with increasing unsaturation in log-phase cells. Similar experiments carried out in D₂O also show an increase in sensitivity, lipid peroxidation and membrane damage, indicating that singlet oxygen may be responsible for such near-UV-radiation-induced damage     

THE ROLE OF SUPEROXIDE AND SINGLET OXYGEN IN LIPID PEROXIDATION

Abstract— An investigation into the mechanism of lipid peroxidation catalyzed by xanthine oxidase showed a dependence upon superoxide, singlet oxygen and adenosine 5'-diphosphate chelated iron (ADP-Fe³⁺). In the absence of ADP-Fe³⁺ or in the presence of superoxide dismutase there is complete inhibition of enzymatic peroxidation. Initiation of peroxidation likely occurs through an ADP-perferryl ion complex formed by ADP-Fe³⁺ and superoxide. Use of the singlet oxygen trapping agent 2,5-diphenylfuran showed that singlet oxygen does not participate in the initiation of peroxidation but rather in the propagation of peroxidation. The mechanisms of NADPH-cytochrome P450 reductase-catalyzed and ADP-Fe²⁺ catalyzed lipid peroxidation parallel that of xanthine oxidase in that initiation occurs through a superoxide dismutase-sensitive reaction and that singlet oxygen is present during propagation of lipid peroxidation.     

钙离子选择性双管复合微电极的研制

本文研制的钙离子选择性双管复合微电极尖端直径小至2.5μm,特别适用于活体组织细胞及临床微量试样中钙离子浓度的测定。用该电极测量了人体微量试样中钙离子浓度,并观察了大白鼠及家免心肌组织受激时钙离子活度的动态变化。     

CYTOPROTECTION AGAINST MEROCYANINE 540-SENSITIZED PHOTOINACTIVATION OF THE Na+,K+-ADENOSINE TRIPHOSPHATASE IN LEUKEMIA CELLS: GLUTATHIONE AND SELENOPEROXIDASE INVOLVEMENT

When irradiated with broad-band visible light in the presence of merocyanine 540 (MC540), murine leukemia L1210 cells grown under selenium-deficient conditions (Se(-) cells) accumulated lipid hydroperoxides and lost viability more rapidly than selenium-satisfied controls (Se(+) cells). These findings suggest that cytoprotection against photoperoxidation and photokilling is mediated at least in part by selenoperoxidase (SePX) action. Similar protection against photoinactivation of an intrinsic membrane enzyme, the Na⁺,K⁺-ATPase, has been observed. Thus, irradiation of MC540-sensitized Se(-) cells resulted in an immediate and progressive inactivation of ouabain-sensitive Na⁺, K⁺-ATPase; by contrast, activity loss in Se(+) cells was preceded by a prominent lag. Enzyme photoinactivation in Se(-) cells was inhibited by ebselen, an SePX mimetic, confirming that SePX(s) is (are) involved in natural protection. Desferrioxamine treatment (iron sequestration/inactivation) resulted in higher hydroperoxide levels and slower Na⁺,K⁺-ATPase inactivation during MC540/light exposure, whereas ferric-8-hydroxyquinoline treatment (iron supplementation) had the opposite effect. Thus, iron appears to play an important role in both of these processes. In contrast, photoinactivation of another intrinsic enzyme in L1210 cells, acetylcholinesterase (AChE), was unaffected by selenium or iron manipulation. On the basis of these findings, we propose that lipid peroxidation plays an important role in the photoinactivation of Na⁺,K⁺-ATPase, but not AChE. This is consistent with the fact that Na⁺, K⁺-ATPase's active site lies within the membrane bilayer, whereas AChE's active site lies outside the bilayer.     

Surface properties of plasma membrane vesicles isolated from melon (Cucumus melo L.) root cells differing in salinity tolerance

The hypotheses that genotypic differences in salinity tolerance may result from (i) differences in global surface charge density or (ii) from differences in global Ca²⁺ binding were tested. An attempt was made to correlate the differing salinity tolerance of four melon cultivars with surface properties of vesicles extracted from the plasma membrane (PM) of their root cells. Surface characterization involved measurements of electrophoretic mobility and sorption of ⁴⁵Ca²⁺ to the vesicles in the presence of varying concentrations of Ca²⁺, Na⁺ and Mg²⁺. Irrespective of salinity tolerance, vesicles from the four cultivars yielded similar ζ potentials under similar conditions, indicating similar global surface charge densities. Sorption studies with vesicles from two cultivars differing in salinity tolerance predicted independently this result of equal surface charge density. The estimated global binding affinities of Ca²⁺, Na⁺ and Mg²⁺ to the PM of both cultivars were the same with binding coefficients of 50, 0.8 and 9 M⁻¹, respectively. Consequently, the hypotheses enumerated above to interpret genotypic differences in salinity toxicity are rejected. However, vesicles from the salt-resistant strain sorbed 19% more Ca²⁺ per given amount of protein in the membrane, indicating the existence of a larger number of negatively charged surface sites per given amount of protein and a smaller amount of protein per given area of membrane. Genotypic differences in site-specific Ca²⁺-binding affinity (e.g. at ion channels) remain a viable hypothesis for genotypic differences in salinity tolerance.     

Calcium Ion Coordinated Polyamide Nanofiltration Membrane for Ultrahigh Perm-selectivity Desalination

Improving the permeate flux but retaining the rejection of thin-film composite(TFC) polyamide nanofiltration(NF) membrane is a high requirement for desalination. In this work, a calcium ion(Ca²⁺) coordinated polyamide(PA) NF membrane was prepared by directly adding CaCl₂ to the piperazine(PIP) aqueous solution during the interfacial polymerization process. Due to the coordination interaction between Ca²⁺ and the amide bond in PA active layer, the number of hydrogen bonds in the PA active layer was reduced, causing in turn the decrease of physical cross-linking degree. As a consequence, the pore of the PA active layer was enlarged, prominently enhancing the water permeance of NF membrane. With the increase of CaCl₂ concentration, the pure water flux of TFC NF increased significantly while the rejection of Na₂SO₄ decreased sightly. Compared with TFC NF membrane prepared without CaCl₂, the permeate flux of the Ca²⁺ coordinated polyamide NF membrane prepared under optimal conditions was increased by 3-4 folds with Na₂SO₄ rejection of 95.26%. Meanwhile, such a Ca²⁺ coordinated PA NF membrane showed a better SO₄^2-/Cl^- selectivity.     

分子动力学模拟电解质对阴非离子表面活性剂界面行为的影响

通过分子动力学(MD)方法研究了不同类型电解质对阴非离子表面活性剂C₁₂EO₃C油水界面性能的影响。运用z轴质量密度分布、径向分布函数、分子间相互作用配位数、空间分布函数及均方根位移五种模拟参数来分析电解质与阴非离子表面活性剂的相互作用情况。研究表明,三种离子的加入均对水分子与表面活性剂亲水基形成的水化层结构产生影响,且从微观层面验证三种离子对表面活性剂亲水基相互作用强度大小顺序为Na⁺ < Ca²⁺ < Mg²⁺。通过扩散模拟结果可以较好地解释离子加入对界面张力平衡时间的影响情况。这对指导实验方向、制订最佳复配方案具有重要意义。     

Studies of Permeabilities of Metallic Ions Through Crosslinked Chitosan Membranes

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DEVELOPMENT OF DOUBLE-BARRELED CALCIUM ION-SELECTIVE MICROELECTRODE

A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients for K+,Na and Mg2+are adequate for in-tracellular measurements of Ca activities.The inner wall of the selective channel was made to be hydrophobic by treatment withalkyl-alcohols.By means of this microelectrode some physiologicalphenomena related to Ca2+activities have been studied,and Caconcentrations in clinical microsamples have also been determined.     

Competitive adsorption of Ca and local anesthetics on lipid membrane surfaces

Adsorption fo tertriary amine local anesthetics and Ca²⁺ onto lipid membranes having various negative surface charge densities was studied by measuring lipid vesicle electrophoretic mobility.

As the surface charge density of the membrane was reduced, the adsorption of the local anesthetics dominated that of the divalent cation. For a relatively high negatively charged membrane, the adsorption of both local anesthetic and Ca²⁺ became comparable and competitive.

It is deduced that the major factor for the adsorption of local anesthetic onto lipid membranes is due to simple physical partitioning between aqueous and membrane phases, and not due to ionic type of binding as seen for divalent cations with membranes. However, the adsorption of anesthetics is influenced by the surface potential of membranes which is in turn related to the surface concentration of local anesthetics near the membrane.

The amounts of competitive adsorption of divalent cations and local anesthetics are analyzed with respect to their bulk concentrations and various surface charge densities of the membranes. With the results of the above studies, a possible interpretation for the interaction site as well as the mode of adsorption of local anesthetics onto axon membranes is made in relation to divalent cation concentrations in the bulk phases.     

PROOXIDANT and ANTIOXIDANT EFFECTS OF ASCORBATE ON PHOTOSENSITIZED PEROXIDATION OF LIPIDS IN ERYTHROCYTE MEMBRANES

Abstract— Continuous blue light irradiation of resealed erythrocyte ghosts at 37°C in the presence of uroporphyrin or protoporphyrin results in ¹O₂-mediated (azide inhibitable) lipid peroxidation and membrane lysis. Lipid peroxidation was assessed by thiobarbituric acid reactivity and by quantitation of total hydroperoxides, while lysis was measured in terms of trappedglucose–6-P release. Low concentrations of ascorbate, AH^- (e.g. 0.5 m M ). present at the start of irradiation, significantly enhanced the rates of lysis and peroxidation, whereas relatively high concentrations of AH^- (e.g. 15 m M ) inhibited both processes. By way of contrast. AH^- produced only a dose-dependent inhibition of the photoinactivation of lysozyme, added as an extramembranous target. No significant AH^-induced lipid peroxidation was observed in dark or light controls, plus porphyrin or minus porphyrin, respectively. Stimulation of peroxidation and lysis by low levels of AH^- was enhanced by added Fe(III), abolished by EDTA. but unaffected by catalase or superoxide dismutase. A plausible explanation for these results is as follows. At low concentrations of AH^- prooxidant activity is favored. Redox metal-mediated breakdown of photoperoxides occurs, which tends to amplify lipid peroxidation. Neither O₂^- nor H₂O₂ appears to be involved. At significantly high concentrations, AH^- acts predominantly as an antioxidant by intercepting ¹O₂ and/or sensitizer triplet, or by scavenging free radical intermediates of lipid peroxidation.     

Interaction and aggregation of lipid vesicles (DLVO theory versus modified DLVO theory)

Interaction and aggregation of acidic phospholipid (phosphatidylserine) vesicles were studied with variation of cation species and their concentrations in vesicle suspensions, and of vesicle sizes. Aggregation was determined by measuring turbidity of vesicle suspension. The experimental results of aggregation of vesicles induced by monovalent cations (Na⁺, K⁺, Cs⁺ and TMA⁺) were explained well in terms of the interaction energy of two interacting vesicles using the ordinary Derjaguin–Landau–Verwey–Overbeek (DLVO) theory for both small and large lipid vesicles. However, the experimental results of aggregation of vesicles induced by divalent cations (Ca²⁺, Mg²⁺ and Ba²⁺) were not explained by the ordinary DLVO theory. In order to explain the experimental results of these vesicle aggregation phenomena, it was necessary to modify the theory by including hydration interaction energies which are due to hydrated water at membrane surfaces, and their magnitude and sign depend upon the nature (hydrophobicity) of the membrane surface.     

卤化银微晶中掺杂的Ca离子对其性能的影响

本文研究了在卤化银微晶沉淀过程中不同量的Ca离子掺杂对其离子电导和照相性能的影响。掺杂Ca离子使卤化银乳剂的介电损耗曲线上的吸收峰向低频方向移动。相应卤化银乳剂的感光度也有一定程度的提高。     

氧化镥中杂质对铈掺杂硅酸镥多晶粉体光谱性质影响

氧化镥中杂质元素对其分离制备工艺、生产成本及镥基硅酸盐闪烁晶体的性能有很大影响,但杂质元素对晶体的性质影响研究较为有限,有待进一步完善。 本文采用高温固相法制备了Lu₂O₃分离过程中关键杂质元素Yb³⁺和Ca²⁺共掺杂Lu₂SiO₅∶Ce多晶粉体,研究了Yb³⁺或Ca²⁺含量对多晶粉体光谱性质的影响,结果表明:Yb³⁺或Ca²⁺共掺并未改变发射光谱的形状和位置,随着杂质元素摩尔分数的增加,光谱强度和荧光寿命逐渐降低。     

Effect of La on heat production by mitochondria isolated from hybrid rice

The effect of lanthanum on mitochondria isolated from hybrid rice Fengyou 559 (Oryza sativa L.) was investigated. Through in vivo culture, low-dose La³⁺ promoted, but higher dose La³⁺, restrained mitochondrial heat production. However, through in vitro incubation, La³⁺ manifested only inhibitory action on mitochondrial energy turnover, the concentration required for 50% and 100% inhibition being 50.9 and 230.2 μM (57.6 nmol/mg protein), respectively. In addition, La³⁺, like Ca²⁺, induced rice mitochondrial swelling and decreased membrane potential (Δψ), which was inhibited by the specific permeability transition inhibitor cyclosporine A (CsA). The induction approached a constant limitation while mitochondrial metabolism was completely prevented by La³⁺, and microscopy observation showed a high disruption of inner mitochondrial membrane in this state. These results demonstrated that lanthanum influenced rice mitochondria in vivo and in vitro via different action pathways, and the latter involved the opening of rice mitochondrial permeability.     

Influence of K+, Na+ or Ca2+ Ions on the Interaction Between AmB and Saturated Phospholipids by Langmuir Technique

Interaction between amphotericin B(AmB) and cell membrane is influenced by different metal cations. In the presence of K⁺, Na⁺ or Ca²⁺ ions, the surface pressure-area isotherms and the elastic modulus of an amphotericindipalmitoylphosphatidylcholine(AmB-DPPC) mixed monolayer were discussed. And the excess free energy and entropies of mixing were calculated according to the surface pressure-area isotherms. The phase transition of the mixed monolayer needed a higher concentration of AmB in the sequence Na⁺ > pure buffer > K⁺ > Ca²⁺. When the molar fraction of AmB(x_AmB) was 0.5, the molecular interaction changed from attraction to repulsion and the mixed monolayer turned to ordered state from disorder state under the induction of K⁺ or Ca²⁺ ions at all surface pressure in our experiment. At high surface pressure, the disorder of monolayer enhanced in the presence of Na⁺ ions at x_AmB > 0.1. At different molar ratios of AmB, the influences of these metal cations were discrepant. These cations may influence AmB molecules to form pores on the monolayer. It is helpful to understand the reduction of AmB's toxicity as theoretical reference.