共查询到20条相似文献,搜索用时 15 毫秒
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Molecular operations of the sodium-calcium exchanger revealed by conformation currents 总被引:10,自引:0,他引:10
The sodium-calcium exchanger is critical in the normal functioning of many cells. In heart muscle, it is the principal way by which the cells keep the concentration of intracellular calcium low, pumping out the Ca2+ that enters the cytosol through L-type Ca2+ channels. The exchanger may also contribute to the triggering of Ca2+ release during voltage-activated excitation-contraction coupling in heart. Time resolved examination of the conformational changes of macromolecules in living cells has so far been largely restricted to ion-channel proteins whose gating is voltage-dependent. We have now directly measured electrical currents arising from the molecular rearrangements of the sarcolemmal Na-Ca exchanger. Changes in the conformation of the exchanger protein were activated by a rapid increase in the intracellular calcium concentration produced by flash photolysis of caged calcium in voltage-clamped heart cells. Two components of membrane current were produced, reflecting a calcium-dependent conformational change of the transporter proteins and net transport of ions by the exchanger. The properties of these components provide evidence that the Na-Ca exchanger protein undergoes two consecutive membrane-crossing molecular transitions that each move charge, and that there are at least 250 exchangers per micron 2 turning over up to 2,500 times per second. 相似文献
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The expression of immunodeficiency in patients with specific purine enzyme defects indicates a crucial role of the purine salvage pathway in the acquisition and expression of normal immune function. One current hypothesis links the failure of normal lymphocyte development in these diseases to the accumulation of deoxynucleotide triphosphates. In our studies of human in vitro IgM responses, we observed that antigen-induced T-suppressor cell activity was abrogated in the presence of micromolar concentrations of deoxyguanosine (dGuo). In contrast, more than 1,000-fold higher resistance to dGuo was found for both noin-proliferative T-helper cell activity and the differentiation and proliferation of the precursor B lymphocytes for direct haemolytic plaque forming cells (PFC). To determine whether these observations could have in vivo relevance, we monitored the generation of murine T-suppressor cells, capable of abrogating a primary IgM response. It was found that dGuo (but not guanosine) selectively inhibited the in vivo development of T-suppressor cells. 相似文献
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ZSM-5型分子筛是60年代末美国Mobil公司开发的一种高硅沸石。此后,人们已将多种杂原子引入ZSM-5骨架,但Ge-ZSM-5型分子筛的研究尚未见报导。我们分别在F~-离子存在的微酸性介质和碱性介质中合成了Ge-ZSM-5型分子筛,并考察了锗对分子筛的形成及其结构参数产生的影响,充分证明锗对ZSM-5骨架上的硅发生了同晶取代。 相似文献
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Enveloped viruses have evolved complex glycoprotein machinery that drives the fusion of viral and cellular membranes, permitting entry of the viral genome into the cell. For the paramyxoviruses, the fusion (F) protein catalyses this membrane merger and entry step, and it has been postulated that the F protein undergoes complex refolding during this process. Here we report the crystal structure of the parainfluenza virus 5 F protein in its prefusion conformation, stabilized by the addition of a carboxy-terminal trimerization domain. The structure of the F protein shows that there are profound conformational differences between the pre- and postfusion states, involving transformations in secondary and tertiary structure. The positions and structural transitions of key parts of the fusion machinery, including the hydrophobic fusion peptide and two helical heptad repeat regions, clarify the mechanism of membrane fusion mediated by the F protein. 相似文献
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用CNDO/2方法研究了A1PO_4-5,MAPO-5和CoAPO-5分子筛的酸性和热稳定性,其酸性大小以q_H~(+-)q_0表征。结果表明,用q_H(+-)q_o来表征酸性比用q_H+来表征更为合理。 用金属原子(Al,Mg,Co)和其周围氧原子总的wibef键序之和来衡量热稳定性,结果与实验事实相符。 相似文献
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ZSM-5 沸石膜的气体分离特性 总被引:1,自引:0,他引:1
采用预吸附溶胶和重复晶化工艺,在多孔不锈钢管外表面制备了ZSM5分子筛膜,SEM观察表明,膜层晶体紧密地相互交联,厚度约25μm,H2对N2,O2和CO2的分离系数分别是448,427和513,明显超过Knudsen扩散理论选择性数值,而且这些分离系数的差别表明所制备的分子筛膜具有分子筛分效应. 相似文献
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用水热法合成了磷酸铁锰铝分子筛(FeMnAPO-5)。通过红外光谱、穆斯堡尔谱等进行了结构和性能研究。实验结果表明,铁和锰已进入了分子筛骨架。 相似文献
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在弱酸性介质和氟离子存在下,以二乙氨基乙醇为模板剂,采用水热法合成了磷酸锗铝分子筛GeAPO-5。并对其结构和性能进行了表征。研究确证了Ge对AlPO_4-5分子筛骨架的同晶取代。 相似文献
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高分子量激肽原第5结构域的研究进展 总被引:1,自引:0,他引:1
高分子激肽原的第5结构域在抑制细胞粘附和浸润、抑制内皮细胞增生、诱导细胞凋亡、参与炎症反应等方面发挥着重要作用.其反应机制可能与高分子激肽原在激肽释放酶的作用下释放缓激肽后,增加其轻链的第5区的暴露面积、增加第5区与内皮细胞的接触机会有关.研究高分子激肽原第5区的作用,有助于预防恶性肿瘤的增长和转移、炎症效应的调节和控制,并为临床上生物治疗的应用奠定实验基础. 相似文献
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从1-苯基-3-甲基-5-吡唑啉酮(PMP)和烟酰氯(异烟酰氯)出发,合成了4-酰代吡啶(-3)吡唑啉-5-酮(化合物A)和4-酰代吡啶(-4)吡唑啉-5-酮(化合物B),利用Sybl6.3软件包分子力学计算程序中的限制性系统搜索,随机搜索和分子动力学计算软件中的模拟退火程序分别对化合物A和B的酮式和烯醇式构象分子(C和D)进行了计算,得到了它们的低能构象集,发现它们具有适宜的配位环境。 相似文献
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The conformation of membranes 总被引:18,自引:0,他引:18
R Lipowsky 《Nature》1991,349(6309):475-481
Membranes composed of amphiphilic molecules are highly flexible surfaces that determine the architecture of biological systems and provide a basic structural element for complex fluids such as microemulsions. Physical theories have been developed to describe many aspects of their conformational behaviour, such as the preferred shapes and shape transformations of closed vesicles, and the shape fluctuations, random-surface configurations, and adhesion and unbinding of interacting membranes. Understanding of these phenomena has been much improved through fruitful interactions between theory and experiment. 相似文献
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L P McIntosh I Grieger F Eckstein D A Zarling J H van de Sande T M Jovin 《Nature》1983,304(5921):83-86
Poly[d(G-C)] serves as the prototype for the right-to-left (B to Z) transition in he helical sense of DNA, both in solution and inthe crystal form. However, the question remains as to which other synthetic and natural DNAs have the potential to adopt left-handed conformations. One logical candidate is the canonical alternating purine-pyrimidine sequence d(A-C)n.d(G-T)n which seems to be widely disseminated in eukaryotic genomes. Our approach to this question is based on the enzymatic synthesis of poly[d(A-C).d(G-U)] derivatives with systematic methyl and halogen substitutions in the C-5 position of the pyrimidines C and U. Such modifications in poly[d(G-C)] have previously been shown to potentiate the B to Z transition. Here we report a highly cooperative, reversible, salt- and temperature-dependent transition for poly[d(A-m5C).d(G-T)], a repeat of the d(A-m5C) sequence which may occur in natural DNA. Spectroscopic studies and the demonstrated ability to bind anti-Z-DNA antibodies suggest that the new helical conformation is left-handed and shares structural features with known Z-DNA. However, a novel property, not exhibited by poly[d(G-C)], is the profound temperature dependence of the conformational equilibrium. 相似文献
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用重量法测试了CoAlPO4-5分子筛对甲苯的吸附. 结果表明,不同温度下的吸附等温线均属典型Ⅰ型,可以用Langmuir方程来描述. 甲苯的吸附自由能变化随吸附量的增加而增加;吸附熵随吸附量的增加而减小,在吸附量大于0.65 mmol/g时变化较大,表明吸附相中分子间的相互作用开始加强;吸附熵与吸附温度无关. 相似文献
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B-ZSM-5 molecular sieve was prepared with gas-solid replacement reaction. The parent zeolite, silicalite-Ⅰ was treated by BBr_3 vapour at 550℃. XRD, IR, XPS, and ~(29)Si MAS NMR techniques show that boron is introduced into the framework of silicalite-Ⅰzeolite. 相似文献