水稻幼苗根细胞质膜和液泡膜微囊Ca^2＋－ATP酶的特性

水稻幼苗根质膜和液泡膜Ca2+-ATP酶对ATP的Km值分别为7.1和4.5 μ mol·L-1;反应的最适pH分别为8.0和7.0.两者活性均受Na3VO4和曙红B(EB)抑制;CPZ抑制质膜Ca2+-ATP酶活性,但促进液泡膜Ca2+-ATP酶活性.30mmol·L-1CaCl2浸种和CaCl2浸种结合低温锻炼预处理,均可提高此酶的活性和冷稳定性.     

低温、高pH胁迫对水稻幼苗根系质膜、液泡膜ATP酶活性的影响

以耐冷性不同的两个水稻品种为材料,比较研究了幼苗根系质膜、液泡膜ATP酶对低温(8℃)及高pH(8.0)胁迫的反应。结果表明水稻根细胞质膜和液泡膜上均存在Ca3+-ATP酶,但活性远低于H+-ATP酶。耐冷品种武育粳3号经低温(8℃)处理2d,根系质膜和液泡膜H+-ATP酶、Ca2+-ATP酶活性均明显升高,至冷处理12d,H+-ATP酶、Ca2+-ATP酶活性有所下降,但仍与对照相近;而冷敏感品种汕优63经低温(8℃)处理2d,根系质膜H+-ATP酶活性略有升高,而质膜Ca2+-ATP酶以及液泡膜H+-ATP酶、Ca2+-ATP酶活性已明显下降;至冷处理12d,4种酶活性均明显低于对照。高pH胁迫使质膜和液泡膜H+-ATP酶活性下降,而使Ca2+-ATP酶活性上升。高pH胁迫会加剧低温冷害。结果表明,耐冷品种质膜、液泡膜ATP酶比冷敏感品种对低温胁迫有更强的适应能力。     

铝和铝+钙对小麦幼苗根尖质膜、液泡膜微囊ATP酶和膜流动性的影响

研究了铝和铝 钙对小麦幼苗根尖质膜、液泡膜微囊H ATP酶、Ca2 ATP酶、Mg2 ATP酶活性及其动力学参数和膜流动性的影响。在质膜和液泡膜微囊制剂中加入 1.0mmol/L的Al3 (AlCl3)时 ,H ATP酶、Ca2 ATP酶、Mg2 ATP酶活性和酶促反应的Vmax及膜流动性下降 ,而酶促反应的最适pH和Km 均不受影响。提高酶促反应介质的Ca2 (CaCl2 )浓度可以缓解Al3 对膜ATP酶活性和膜流动性的影响。推测Al3 可能通过与膜的结合而抑制膜ATP酶的活性     

甲基紫精对水稻幼苗根细胞膜微囊Ca2+-ATP酶活性的影响

10μmool/L甲基紫精(MV)预处理水稻幼苗可明显提高其抗冷力,但这种功效可被钙的螯合剂EGTA(10 mmol/L)和钙调素(CaM)的抑制剂氯丙嗪(CPZ,0.5 mmol/L)所抑制.MV预处理提高了幼苗质膜、液泡膜Ca2+-ATP酶活性,同时也有提高质膜Fe(CN)3-6还原速率和这些活性的冷适应性,但这些效果均可被EGTA和CPZ所抑制.离体条件下,膜微囊的Ca2+-ATP酶活性对H2O2、O-2、-OH敏感.结果显示,MV预处理提高幼苗的抗冷力可能是通过钙信使介导起作用的,钙信使或CaM可能刺激了质膜、液泡膜Ca2+-ATP酶活性;而该预处理有增加质膜、液泡膜Ca2+-ATP酶的冷稳定性则可能与该处理有提高细胞抗氧化能力、稳定冷胁迫下细胞膜系统结构有关.     

抗寒剂CR-4 对冬小麦幼苗质膜钙泵（Ca2 +-ATPase） 的稳定作用

通过磷酸铈沉淀的细胞化学观察揭示,常温下生长的冬小麦幼苗的Ca2+ -ATP酶活性主要定位在质膜上,同时,水浸种和抗寒剂浸种的小麦质膜Ca2+ -ATP酶活性没有差异。然而,小麦幼苗经-7℃冰冻处理12小时和24小时后,则表现明显的区别：水浸种的小麦幼苗质膜Ca2+ -ATP酶活性明显下降,直至完全失活,细胞的精细结构也同时被破坏;而经抗寒剂浸种的小麦幼苗质膜Ca2+ -ATP酶仍维持较高的活性,细胞结构也保持完整,显示抗寒剂对质膜Ca2+ -ATPase酶起着明显的稳定作用。     

Ca2+预处理对热胁迫下辣椒叶肉细胞中Ca2+-ATP酶活性的影响

在常温下生长的辣椒(Capsicum annum L.)叶肉细胞中Ca2+-ATP酶主要分布于质膜、液泡膜上,叶绿体的基质和基粒片层上也有少量分布;在40℃下热胁迫不同的时间,酶活性逐渐下降,直至叶绿体超微结构解体.同样条件下,经过Ca2+预处理后,分布在上述细胞器膜或片层上的酶活性大大提高,表明Ca2+预处理对该酶活性具有激活作用;Ca2+预处理对热胁迫下的超微结构的完整性具有一定的保护作用,并且能使Ca2+-ATP酶在热胁迫下维持较高活性.结果表明,Ca2+预处理增强辣椒幼苗的抗热性,可能与其稳定细胞膜、从而使Ca2+-ATP酶在热胁迫下保持较高活性有一定关系.     

钙对亚适温弱光下黄瓜幼苗Ca2+分布及叶绿素荧光参数的影响

以'津优3号'黄瓜幼苗为试验材料,采用焦锑酸钙沉淀的电镜细胞化学方法,研究了CaCl2预处理对亚适温(昼/夜18℃/12℃)弱光(100 μmol·m-2·s-1)下黄瓜幼叶细胞中Ca2+分布、Ca2+-ATP酶活性及叶绿素荧光参数的影响.结果显示:正常温光条件(CK)下,黄瓜幼叶细胞Ca2+主要存在于液泡和液泡膜上,细胞质中含量较低;经亚适温和弱光处理7 d后,叶片细胞质和细胞膜中形成较大的钙沉淀颗粒,液泡中的Ca2+颗粒聚集成团,膜组织边缘模糊,Ca2+-ATPase活性降低;胁迫前用CaCl2预处理的细胞质中Ca2+颗粒略有增加,且分布较均匀,膜组织完整,Ca2+-ATPase活性与CK差异不显著;而经LaCl3、EGTA和CPZ预处理的Ca2+多呈大颗粒状聚积在细胞质、液泡膜或细胞壁上,Ca2+-ATPase活性大幅度下降.在7 d亚适温弱光处理后,各处理黄瓜叶片的Fv/Fm变化不大,而ΦPSⅡ、qP和ETR显著降低;与水预处理相比,叶片ΦPSⅡ、qP和ETR在CaCl2处理下显著增加,而在EGTA和CPZ处理下显著减小,LaCl3处理的无显著变化.研究表明,亚适温弱光处理能打破黄瓜幼苗细胞内的Ca2+平衡,使其膜组织受到一定程度破坏;CaCl2可维持胞内较高的Ca2+-ATP酶活性,保持Ca2+平衡,保护细胞膜组织结构完整,并参与了光合作用光能捕获和光合效率的调控,能有效减轻亚适温弱光对黄瓜幼苗光合作用的不良影响.     

甲基紫精对水稻幼苗根细胞膜微囊Ca^2＋-ATP酶活性的影响

10μmol／L甲基紫精(MV)预处理水稻幼苗可明显提高其抗冷力,但这种功效可被钙的螯合剂EGTA(10 mmol／L)和钙调素(CaM)的抑制剂氯丙嗪(CPZ,0．5mmol／L)所抑制。MV预处理提高了幼苗质膜、液泡膜Ca^2 -ATP酶活性,同时也有提高质膜Fe(CN)6^3-还原速率和这些活性的冷适应性,但这些效果均可被EGTA和CPZ所抑制。离体条件下,膜微囊的Ca^2 -ATP酶活性对H2O2、O2^-、-0H敏感。结果显示,MV预处理提高幼苗的抗冷力可能是通过钙信使介导起作用的,钙信使或CaM可能刺激了质膜、液泡膜Ca^2 -ATP酶活性;而该预处理有增加质膜、液泡膜Ca^2 -ATP酶的冷稳定性则可能与该处理有提高细胞抗氧化能力、稳定冷胁迫下细胞膜系统结构有关。     

NaCl胁迫下大麦根系液泡膜H+-ATP酶活性受ATP和焦磷酸含量的调节

选用两个耐盐性强弱不同的大麦(Hordeumvulgare L.)品种,研究了NaCl胁迫下其幼苗根中ATP和焦磷酸(PPi)含量的变化以及PPi对液泡膜H -ATP酶活性的影响.结果表明:在含NaCl 200mmol/L的1/2 Hoagland溶液中处理2 d,耐盐品种(滩引2号)根中液泡膜H -ATP酶活性增加,然后逐渐下降,而H -PPi酶活性在NaCl处理9 d中'直下降.盐敏感品种(科品7号)在NaCl胁迫下根中H -ATP酶和H -PPi酶活性都下降(图1).与对照相比较,NaCl胁迫下耐盐品种根中ATP含量2 d时增加,4 d后下降;盐敏感品种根中ATP积累受NaCl胁迫的抑制(图2).NaCl胁迫下,两品种的PPi含量皆略有增加(图3).PPi对液泡膜H -ATP酶活性有竞争性抑制作用(图4).结果表明:ATP积累是NaCl胁迫下液泡膜H -ATP酶活性增加的原因之一,NaCl胁迫下大麦品种根中ATP含量下降和PPi对液泡膜H -ATP酶的抑制使该酶活性下降.     

钙对盐胁迫下棉苗离子吸收分配的影响

研究了钙对NaCl胁迫下棉花幼苗体内离子分布的影响及其与根系质膜H+-ATP酶、液泡膜H+-ATP酶和H+-PP酶活性的关系。不同器官离子含量和根系横切面X-射线微区分析结果表明,NaCl胁迫下外源钙明显减少棉花幼苗对Na+的吸收及其向茎杆、叶片的运输,增加对K+和Ca2+的吸收及其向茎杆、叶片的运输,增强棉苗体内的盐分区域化分配,提高根冠比和干物质积累,根系电解质渗漏率下降。钙明显提高盐胁迫下幼根细胞质膜H+-ATP酶、液泡膜H+-ATP酶和H+-PP酶的活性,与钙调节棉花对离子的吸收、分配相一致,说明这些酶可以为根细胞中的Na+在液泡中积累以及K+、Ca2+的选择性吸收和运输提供动力。     

红细胞膜蛋白与膜骨架

近10多年红细胞膜领域的研究取得了可观的进展,在红细胞膜蛋白的结构-功能相关和相互作用以及红细胞膜障碍多方面都有新的发现和开拓．现主要就国内外有关报道作一扼要综述,涉及红细胞膜蛋白的组成、功能及其相互作用,红细胞膜骨架和红细胞膜蛋白疾病等研究进展．     

大鼠脑突触质膜糖皮质激素受体的纯化

本文利用抗大鼠肝细胞内糖皮质激素受体的单克隆抗体制备的免疫亲和层析柱,将大鼠脑突触质膜糖皮质激素受体纯化了约1150倍,SDS聚丙烯酰胺簿层梯度凝胶电泳显示,在约67kD处有一较明显的染色条带。     

易位子辅助膜蛋白插入热力学

易位子辅助膜蛋白插入内质网膜是膜蛋白质生物生成的关键过程。了解不同类分子插入生物膜的机制是预测溶质分子透膜速度的先决条件,这也是药物设计和药理学领域的关键因素。根据插入机制,可以设计插膜肽直接用于疾病治疗,或者作为载体有选择性地将药物靶向特定细胞。自从2004年第1个易位子通道蛋白（Sec）的晶体结构被解析后,近十几年来大量的实验和理论研究,都在致力于揭示Sec辅助膜蛋白插入过程的分子机制。本文总结了过去该领域的实验和分子动力学模拟研究进展,从热力学方面重点分析了造成膜蛋白插入自由能分子动力学模拟计算值,以及实验值间偏差的原因。其中,根据研究条件精确设置模拟参数、插入造成的膜变形对自由能计算有很大的影响;核糖体为新生肽插入到Sec通道过程提供了能量,核糖体与Sec的结合影响Sec侧门的开放程度和Sec通道的结构,从而降低膜插入自由能。Sec辅助膜蛋白插入是一个极其复杂的过程,但整个过程仍然符合热力学和动力学的基本原理,尽管疏水性是Sec辅助膜蛋白质插入的关键性因素,但也不能忽略动力学因素的影响。     

Tamoxifen Increases Membrane Fluidity at High Concentrations

There are contradictory results in the literature relating to the effect oftamoxifen on membrane fluidity. The present work investigates the effect oftamoxifen on membrane dynamics to find out whether the concentration oftamoxifen can be one of the factors in this discrepancy. Turbidity(absorbance at 440 nm) and Fourier transform infrared spectroscopicstudies reveal that tamoxifen causes opposite effects on membranefluidity at low (1 mol.%) and high (30 mol.%) tamoxifen concentrations. Lowtamoxifen concentrations increase the absorbance in the gel and liquidcrystalline phase, whereas high tamoxifen concentrations decrease theabsorbance in gel and liquid crystalline phase, whereas tamoxifenconcentrations decrease the absorbance. Observations on both phasesshow that the bandwidth of the CH2 stretching bands decreases with1 mol.% tamoxifen and increases with 30 mol.% tamoxifen present, indicatinga decrease in membrane fluidity at low tamoxifen concentrations and anincrease in fluidity at high tamoxifen concentrations. It is seen that theapparent discrepancy in the literature on the effect of tamoxifen onmembrane fluidity mainly arises from the tamoxifen concentration used andthe confusion on the concept of lipid fluidity and lipid order.     

Membrane Tethering of SepF,a Membrane Anchor for the Mycobacterium tuberculosis Z-ring

Bacterial cell division begins with the formation of the Z-ring via polymerization of FtsZ and the localization of Z-ring beneath the inner membrane through membrane anchors. In Mycobacterium tuberculosis (Mtb), SepF is one such membrane anchor, but our understanding of the underlying mechanism is very limited. Here we used molecular dynamics simulations to characterize how SepF itself, a water-soluble protein, tethers to acidic membranes that mimic the Mtb inner membrane. In addition to an amphipathic helix (residues 1–12) at the N-terminus, membrane binding also occurs through two stretches of positively charged residues (Arg27-Arg37 and Arg95-Arg107) in the long linker preceding the FtsZ-binding core domain (residues 128–218). The additional interactions via the disordered linker stabilize the membrane tethering of SepF, and keep the core domain of SepF and hence the attached Z-ring close to the membrane. The resulting membrane proximity of the Z-ring in turn enables its interactions with and thus recruitment of two membrane proteins, FtsW and CrgA, at the late stage of cell division.     

膜蛋白的拓扑学

膜蛋白的拓扑学是研究膜蛋白三维结构的出发点．利用融合蛋白和化学修饰等实验技术已确定了很多膜蛋白的拓扑学．对膜蛋白的转运与插膜的研究确定可能存在两类插膜元件．对已知拓扑学的膜蛋白的统计分析以及蛋白质工程的研究表明存在膜蛋白拓扑学的内正规则．目前已形成预测膜蛋白的拓扑学的比较可靠的策略,这在反向生物学上具有重要意义.但要进行三维结构的预测还有许多路要走．     

A New Turgor/Membrane Potential Probe Simultaneously Measures Turgor and Electrical Membrane Potential

Abstract: A new combined turgor/membrane potential probe (T-EP probe) monitored cell turgor and membrane potential simultaneously in single giant cells. The new probe consisted of a silicone oil-filled micropipette (oil-microelectrode), which conducted electric current. Measurements of turgor and hydraulic conductivity were performed as with the conventional cell pressure probe besides the membrane potential. In internodal cells of Chara corallina, steady state turgor (0.5-0.7 MPa) and resting potentials (-200 to ?220 mV) in APW, and hydraulic conductivity (0.07 to 0.21 × 10～⁵ m s^?1 MPa^?1) were measured with the new probe, and cells exhibited healthy cytoplasmic streaming for at least 24 h during measurements. When internodal cells of Chara corallina were treated with 30, 20, 10, and 5 mM KCI, turgor responded immediately to all concentrations, and the osmotic changes in the medium were measured. Action potentials, which brought the membrane potential to a steady depolarization that measured the concentration difference of K⁺ in the medium, were induced in a concentration — dependent delay and occurred only 30, 20, and 10 mM of KCl. When the solution was changed back to APW, the repolarization of membrane potential consisted of a quick and a following slow phase. During the quick phase, which took place immediately and lasted 1 to 3 min, the plasma membrane remained activated. The membrane was gradually deactivated in the slow phase, and entirely deactivated when the membrane potential recovered to the resting potential in APW. Although the activated plasma membrane was permeable to K⁺, no major ion channels were activated on the tonoplast, and therefore, internodal cells of Chara corallina did not regulate turgor when osmotic potential changed in the surrounding medium.     

Membrane Fusion

The fusion of biological membranes results in two bilayer-based membranes merging into a single membrane. In this process the lipids have to undergo considerable rearrangement. The nature of the intermediates that are formed during this rearrangement has been investigated. Certain fusion proteins facilitate this process. In many cases short segments of these fusion proteins have a particularly important role in accelerating the fusion process. Studies of the interaction of model peptides with membranes have allowed for increased understanding at the molecular level of the mechanism of the promotion of membrane fusion by fusion proteins. There is an increased appreciation of the roles of several independent segments of fusion proteins in promoting the fusion process.Many of the studies of the fusion of biological membranes have been done with the fusion of enveloped viruses with other membranes. One reason for this is that the number of proteins involved in viral fusion is relatively simple, often requiring only a single protein. For many enveloped viruses, the structure of their fusion proteins has certain common elements, suggesting that they all promote fusion by an analogous mechanism. Some aspects of this mechanism also appears to be common to intracellular fusion, although several proteins are involved in that process which is more complex and regulated than is fusion.     

醋酸纤维素固定化酰化酶膜的研究

采用正交实验法,考察了铸膜液配比对醋酸纤维素固定化氨基酰化酶微孔滤膜的影响,对酶膜的泡点压力、孔径、孔隙率及透水速率等性能进行了表征.结果表明,铸膜液组合最佳时,酶相对活力产率高达98.2%,酶膜的透水率适当,重复使用10次后仍保留原活力的79.7%,而其存放稳定性也大大提高.