Change of proton motive force across thylakoid membrane in soybean leaf during state transitions

Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission(ms-DLE) during the coures of state transitions which were indicated by the cholrophyll fluores-cence at room temperature and 77K.When dark-adapted leaves were induced to state Ⅰ with far-red light,Fm/F0,F685/F735 and the intensity of fast phase of ms-DLE were af-fected slightly.However,during the induction to state Ⅱ with red light,both Fm/F0 and F685/F735 decreased immedi-ately and the former were quicker than the latter.In this interval,the intesity of fast phase of ms-DLE increased to a maximum and then decreased to a lower valus during the transition to stateⅡ.Nigericin,an uncoupler which elimi-nates the proton gradient across thylakoid membrane,inhib-ited the increase in the intensity of fast phase of ms-DLE during the transition to state Ⅱ.Another uncoupler,valino-mycin,which eliminates the membrane potential,did not affect the changes of the intensity of fast phase.These results suggest that the prompt increase in the intensity of fast phase of ms-DLE at the beginning of transitions to state Ⅱ is cor-related mainly with the proton gradient released from water oxidation in photosystemⅡ.     

人跑的动力再分析

从力学的角度上看,推动人体质心移动的直接动力一定是外力,外力包括各具特点的切向摩擦力和法向弹力.跑动是由引发外力的人体内力在起作用；在引发跑动外力的各种人体内力中,与髋关节相关的肌肉群的影响最大,是最主要的动力群.要提高跑的成绩,应重视髋关节的柔韧性和灵活性锻炼,强化与髋关节相关的肌群的力量.     

Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export

Diverse molecules, from small antibacterial drugs to large protein toxins, are exported directly across both cell membranes of gram-negative bacteria. This export is brought about by the reversible interaction of substrate-specific inner-membrane proteins with an outer-membrane protein of the TolC family, thus bypassing the intervening periplasm. Here we report the 2.1-A crystal structure of TolC from Escherichia coli, revealing a distinctive and previously unknown fold. Three TolC protomers assemble to form a continuous, solvent-accessible conduit--a 'channel-tunnel' over 140 A long that spans both the outer membrane and periplasmic space. The periplasmic or proximal end of the tunnel is sealed by sets of coiled helices. We suggest these could be untwisted by an allosteric mechanism, mediated by protein-protein interactions, to open the tunnel. The structure provides an explanation of how the cell cytosol is connected to the external environment during export, and suggests a general mechanism for the action of bacterial efflux pumps.     

化学实验中创新的动力来源探讨

本文针对需要、兴趣、动机、问题意识等方面探讨了化学实验中创新的动力来源，着重阐述实验兴趣的发展和培养过程，以及问题意识的培养手段，旨在从心理学的角度探讨化学实验中学生创新的动力来源。     

青海城镇体系发展的历史轨迹与动力

青海城镇体系经历了发韧期、奠基期、转型期3个发展历程.在这一过程中,湟水谷地最先拉开了城镇发展的历史帏幕,随后逐步向西扩展进入青海湖地区.宏观上,从农耕区向农牧交错区渗透,进而向游牧区拓展,反映了社会历史进程和地域开发进程的调控作用,因此城镇分布数量和密度呈现出农耕区—农牧交错区—游牧区逐级递减的趋势.中观上,以河流为脉络,城镇发展或溯源而上伸入高原腹地,或向河谷两岸推进,进入山区,表现为从优势生存空间向劣势生存空间的时空转化,城镇数量与密度呈现出川水地区—浅山地区—脑山地区的递减趋势.微观上,河谷农耕区城镇选址多位于河流阶地上,土地肥沃,取水便利;而牧区城镇的选址却往往与水草丰美的牧场相关,映射出古代城镇对自然条件和自然物质基础的依赖性.总体而言,青海省城镇兴起和发展的动力,主要来自于外部中央行政建制和军事据点的设置,而非城镇内部社会经济自我发展.就单个城镇而言,民族文化、民族宗教与民族贸易的亲合关系和响应力,是城镇成长的主要推进剂.     

Direct observation of steps in rotation of the bacterial flagellar motor

The bacterial flagellar motor is a rotary molecular machine that rotates the helical filaments that propel many species of swimming bacteria. The rotor is a set of rings up to 45 nm in diameter in the cytoplasmic membrane; the stator contains about ten torque-generating units anchored to the cell wall at the perimeter of the rotor. The free-energy source for the motor is an inward-directed electrochemical gradient of ions across the cytoplasmic membrane, the protonmotive force or sodium-motive force for H+-driven and Na+-driven motors, respectively. Here we demonstrate a stepping motion of a Na+-driven chimaeric flagellar motor in Escherichia coli at low sodium-motive force and with controlled expression of a small number of torque-generating units. We observe 26 steps per revolution, which is consistent with the periodicity of the ring of FliG protein, the proposed site of torque generation on the rotor. Backwards steps despite the absence of the flagellar switching protein CheY indicate a small change in free energy per step, similar to that of a single ion transit.     

Distinct roles of nerve and muscle in postsynaptic differentiation of the neuromuscular synapse

The development of chemical synapses is regulated by interactions between pre- and postsynaptic cells. At the vertebrate skeletal neuromuscular junction, the organization of an acetylcholine receptor (AChR)-rich postsynaptic apparatus has been well studied. Much evidence suggests that the nerve-derived protein agrin activates muscle-specific kinase (MuSK) to cluster AChRs through the synapse-specific cytoplasmic protein rapsyn. But how postsynaptic differentiation is initiated, or why most synapses are restricted to an 'end-plate band' in the middle of the muscle remains unknown. Here we have used genetic methods to address these issues. We report that the initial steps in postsynaptic differentiation and formation of an end-plate band require MuSK and rapsyn, but are not dependent on agrin or the presence of motor axons. In contrast, the subsequent stages of synaptic growth and maintenance require nerve-derived agrin, and a second nerve-derived signal that disperses ectopic postsynaptic apparatus.     

Complete atomic model of the bacterial flagellar filament by electron cryomicroscopy

The bacterial flagellar filament is a helical propeller for bacterial locomotion. It is a helical assembly of a single protein, flagellin, and its tubular structure is formed by 11 protofilaments in two distinct conformations, L- and R-type, for supercoiling. The X-ray crystal structure of a flagellin fragment lacking about 100 terminal residues revealed the protofilament structure, but the full filament structure is still essential for understanding the mechanism of supercoiling and polymerization. Here we report a complete atomic model of the R-type filament by electron cryomicroscopy. A density map obtained from image data up to 4 A resolution shows the feature of alpha-helical backbone and some large side chains. The atomic model built on the map reveals intricate molecular packing and an alpha-helical coiled coil formed by the terminal chains in the inner core of the filament, with its intersubunit hydrophobic interactions having an important role in stabilizing the filament.     

Structure of the bacterial flagellar protofilament and implications for a switch for supercoiling

The bacterial flagellar filament is a helical propeller constructed from 11 protofilaments of a single protein, flagellin. The filament switches between left- and right-handed supercoiled forms when bacteria switch their swimming mode between running and tumbling. Supercoiling is produced by two different packing interactions of flagellin called L and R. In switching from L to R, the intersubunit distance ( approximately 52 A) along the protofilament decreases by 0.8 A. Changes in the number of L and R protofilaments govern supercoiling of the filament. Here we report the 2.0 A resolution crystal structure of a Salmonella flagellin fragment of relative molecular mass 41,300. The crystal contains pairs of antiparallel straight protofilaments with the R-type repeat. By simulated extension of the protofilament model, we have identified possible switch regions responsible for the bi-stable mechanical switch that generates the 0.8 A difference in repeat distance.     

论构建和谐社会时期公民政策参与的内在动力机制

政治民主化是构建社会主义和谐社会的内在要求。公民政策参与是实现政治民主化的主要形式之一。我国改革开放以来的一系列经济结构、政治体制以及社会组织结构的变迁与发展有力地促进了公民政策参与的发展。     

Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism

The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller. The hook is made of about 120 copies of a single protein, FlgE, and its function as a nano-sized universal joint is essential for dynamic and efficient bacterial motility and taxis. It transmits the motor torque to the helical propeller over a wide range of its orientation for swimming and tumbling. Here we report a partial atomic model of the hook obtained by X-ray crystallography of FlgE31, a major proteolytic fragment of FlgE lacking unfolded terminal regions, and by electron cryomicroscopy and three-dimensional helical image reconstruction of the hook. The model reveals the intricate molecular interactions and a plausible switching mechanism for the hook to be flexible in bending but rigid against twisting for its universal joint function.     

基于网络环境的舰船动力装置监控系统平台开发

针对我国舰船动力监控的技术现状,对国内外几种典型舰船动力监控系统做了比较.采用美国RockWell工业控制网络技术,针对机舱中柴油机、燃气轮机及泵辅系统监控特点,完成了舰船机舱动力装置设备网(DeviceNet)、控制网(ControlNet)和以太网(EtherNet)三层网络体系构架的现场总线控制系统(FCS)的开发,模拟实现了船舶机舱动力装置监控的功能.该平台具有在舰船动力装置监控应用上的智能化、系列化和标准化的特点.     

A conserved mechanism of DEAD-box ATPase activation by nucleoporins and InsP6 in mRNA export

Superfamily 1 and superfamily 2 RNA helicases are ubiquitous messenger-RNA-protein complex (mRNP) remodelling enzymes that have critical roles in all aspects of RNA metabolism. The superfamily 2 DEAD-box ATPase Dbp5 (human DDX19) functions in mRNA export and is thought to remodel mRNPs at the nuclear pore complex (NPC). Dbp5 is localized to the NPC via an interaction with Nup159 (NUP214 in vertebrates) and is locally activated there by Gle1 together with the small-molecule inositol hexakisphosphate (InsP(6)). Local activation of Dbp5 at the NPC by Gle1 is essential for mRNA export in vivo; however, the mechanistic role of Dbp5 in mRNP export is poorly understood and it is not known how Gle1(InsP6) and Nup159 regulate the activity of Dbp5. Here we report, from yeast, structures of Dbp5 in complex with Gle1(InsP6), Nup159/Gle1(InsP6) and RNA. These structures reveal that InsP(6) functions as a small-molecule tether for the Gle1-Dbp5 interaction. Surprisingly, the Gle1(InsP6)-Dbp5 complex is structurally similar to another DEAD-box ATPase complex essential for translation initiation, eIF4G-eIF4A, and we demonstrate that Gle1(InsP6) and eIF4G both activate their DEAD-box partner by stimulating RNA release. Furthermore, Gle1(InsP6) relieves Dbp5 autoregulation and cooperates with Nup159 in stabilizing an open Dbp5 intermediate that precludes RNA binding. These findings explain how Gle1(InsP6), Nup159 and Dbp5 collaborate in mRNA export and provide a general mechanism for DEAD-box ATPase regulation by Gle1/eIF4G-like activators.     

直梁在纵横弯曲耦合振动的动力响应

考察纵横弯曲下直梁的强迫振动的运动方程，利用动响应分析中主振型的正交性，将微分方程解耦合，把多自由度系统转化为单自由度系统的模态响应问题，再将各个模态的响应叠加得到原系统的动力响应，即运动微分方程的解．     

Structure of the C-terminal domain of FliG, a component of the rotor in the bacterial flagellar motor.

Many motile species of bacteria are propelled by flagella, which are rigid helical filaments turned by rotary motors in the cell membrane. The motors are powered by the transmembrane gradient of protons or sodium ions. Although bacterial flagella contain many proteins, only three-MotA, MotB and FliG-participate closely in torque generation. MotA and MotB are ion-conducting membrane proteins that form the stator of the motor. FliG is a component of the rotor, present in about 25 copies per flagellum. It is composed of an amino-terminal domain that functions in flagellar assembly and a carboxy-terminal domain (FliG-C) that functions specifically in motor rotation. Here we report the crystal structure of FliG-C from the hyperthermophilic eubacterium Thermotoga maritima. Charged residues that are important for function, and which interact with the stator protein MotA, cluster along a prominent ridge on FliG-C. On the basis of the disposition of these residues, we present a hypothesis for the orientation of FliG-C domains in the flagellar motor, and propose a structural model for the part of the rotor that interacts with the stator.     

多源流理论视域下我国体教融合政策的变迁动力与优化路径

采用文献资料、专家访谈等方法，基于多源流的公共政策过程分析框架，回溯新中国成立以来我国体教融合政策变迁历程，探求政策变迁的动力，提出促进政策变迁的优化路径。研究认为：我国体教融合政策变迁源于三重动力：高水平运动员与社会脱节严重、青少年体质健康危机、体育教育价值功能的认识偏差等问题，使有关议题进入政策视野，形成问题源流；政策源流中“两会”代表和专家学者的政策建议以及利益相关者的诉求表达是推动体教融合系列政策形成的“政策原汤”；政治源流中党中央执政理念的与时俱进、国民情绪的舆论导向以及国际体教融合的环境引领示范，为体教融合政策的形成奠定了坚实的政治基础。三大源流交互耦合，合力推动了体教融合政策的变迁。未来，各部门应密切关注待解决现实问题，持续监督与反馈政策矛盾与危机；搭建充分的利益表达平台，形成体教融合政策共同体良性互动机制；践行国家改革理念和发展战略，优化体教融合问题治理环境；发挥政策企业家的正向作用，增加体教融合“政策之窗”的开启频率。     

A role for the two-helix finger of the SecA ATPase in protein translocation

An important step in the biosynthesis of many proteins is their partial or complete translocation across the plasma membrane in prokaryotes or the endoplasmic reticulum membrane in eukaryotes. In bacteria, secretory proteins are generally translocated after completion of their synthesis by the interaction of the cytoplasmic ATPase SecA and a protein-conducting channel formed by the SecY complex. How SecA moves substrates through the SecY channel is unclear. However, a recent structure of a SecA-SecY complex raises the possibility that the polypeptide chain is moved by a two-helix finger domain of SecA that is inserted into the cytoplasmic opening of the SecY channel. Here we have used disulphide-bridge crosslinking to show that the loop at the tip of the two-helix finger of Escherichia coli SecA interacts with a polypeptide chain right at the entrance into the SecY pore. Mutagenesis demonstrates that a tyrosine in the loop is particularly important for translocation, but can be replaced by some other bulky, hydrophobic residues. We propose that the two-helix finger of SecA moves a polypeptide chain into the SecY channel with the tyrosine providing the major contact with the substrate, a mechanism analogous to that suggested for hexameric, protein-translocating ATPases.     

土工格网结构形状对内力传递及加筋作用的影响

为了对不同土工格网的结构形状对其内力传递的影响进行分析,通过与正方形及等边菱形土工格网进行比较,指出正六边形土工格网能使荷载均匀地扩散到所铺设的较大范围内,初步阐明了正六边形土工格网所能发挥加筋作用的优越性.