Single sodium channels from rat brain incorporated into planar lipid bilayer membranes

A voltage- and time-dependent conductance for sodium ions is responsible for the generation of impulses in most nerve and muscle cells. Changes in the sodium conductance are produced by the opening and closing of many discrete transmembrane channels. We present here the first report of electrical recordings from voltage-dependent sodium channels incorporated into planar lipid bilayers. In bilayers with many channels, batrachotoxin (BTX) induced a steady-state sodium current that was blocked by saxitoxin (STX) at nanomolar concentrations. All channels appeared in the bilayer with their STX blocking sites facing the side of vesicle addition, allowing us to define that as the extracellular side. Current fluctuations due to the opening and closing of single BTX-activated sodium channels were voltage-dependent (unit conductance, 30 pS in 0.5 M NaCl): the channels closed at large hyperpolarizing potentials. Slower fluctuations of the same amplitude, due to the blocking and unblocking of individual channels, were seen after addition of STX. Block of the sodium channels by STX was voltage-dependent, with hyperpolarizing potentials favouring block. The voltage-dependent gating, ionic selectivity and neurotoxin sensitivity suggest that these are the channels that normally underlie the sodium conductance change during the nerve impulse.     

AQ膜固定的亚甲蓝修饰电极的电催化特性

制备了亚甲基蓝阳离子掺杂于聚合物AQ中的化学修饰电极。研究了修饰电极的电化学行为，发现该电极在硫酸溶液中进行伏安扫描时具有良好的稳定性。该修饰电极对对多巴胺有较强的催化作用。     

胞腔范畴的一个等价定义

推广了代数中胞腔理想的概念到范畴的层次,并且通过研究范畴的理想链,给出了胞腔范畴的一个等价定义．      

RecBCD enzyme is a bipolar DNA helicase

Escherichia coli RecBCD is a heterotrimeric helicase/nuclease that catalyses a complex reaction in which double-strand breaks in DNA are processed for repair by homologous recombination. For some time it has been clear that the RecB subunit possesses a 3' --> 5' DNA helicase activity, which was thought to drive DNA translocation and unwinding in the RecBCD holoenzyme. Here we show that purified RecD protein is also a DNA helicase, but one that possesses a 5' --> 3' polarity. We also show that the RecB and RecD helicases are both active in intact RecBCD, because the enzyme remains capable of processive DNA unwinding when either of these subunits is inactivated by mutation. These findings point to a bipolar translocation model for RecBCD in which the two DNA helicases are complementary, travelling with opposite polarities, but in the same direction, on each strand of the antiparallel DNA duplex. This bipolar motor organization helps to explain various biochemical properties of RecBCD, notably its exceptionally high speed and processivity, and offers a mechanistic insight into aspects of RecBCD function.     

Direct enzyme transfer from lymphocytes is specific

Lymphocytes are known to interact directly with other cells in vivo and in vitro, and have recently been shown to transfer the lysosomal enzyme, beta-glucuronidase, to fibroblasts from patients with an inherited deficiency of the enzyme. This process requires cell-cell contact, is unaffected by inhibitors of 'classical' receptor-mediated endocytosis and is abolished by inhibitors of protein synthesis. Although it is not yet known to what extent the transfer of enzymes by direct cellular interaction is a general phenomenon, a similar mechanism could possibly be involved in the transfer of other lysosomal enzymes in vivo and in the exchange of protein in vitro. We show here that the direct transfer of enzymes from lymphocytes to fibroblasts is restricted to only certain lysosomal enzymes.     

The cellular machinery of Ferroplasma acidiphilum is iron-protein-dominated

Ferroplasma is a genus of the Archaea, one of the three branches of the tree of life, and belongs to the order Thermoplasmatales (Euryarchaeota), which contains the most acidophilic microbes yet known. Ferroplasma species live in acid mine drainage, acidic pools and environments containing sulphidic ores such as pyrite and characterized by pH values of 0-2 and high concentrations of ferrous iron and other heavy metals. F. acidiphilum strain Y(T) is a chemoautotroph that grows optimally at pH 1.7 and gains energy by oxidizing ferrous iron and carbon by the fixation of carbon dioxide. Here we show that 86% of 189 investigated cellular proteins of F. acidiphilum are iron-metalloproteins. These include proteins with deduced structural, chaperone and catalytic roles, not described as iron-metalloproteins in any other organism so far investigated. The iron atoms in the proteins seem to organize and stabilize their three-dimensional structures, to act as 'iron rivets'. Analysis of proteins of the phylogenetic neighbour Picrophilus torridus and of the habitat neighbour Acidithiobacillus ferrooxidans revealed far fewer and only typical metalloproteins. F. acidiphilum therefore has a currently unique iron-protein-dominated cellular machinery and biochemical phylogeny.     

王阳明"心外无物"思想探微

以理、物、事三个核心概念的新阐释为基点论述了王阳明的心学体系,提出王学的体系是基于价值意义关系的建立,进而分析了王学的内在思维特质以及与朱熹理学的关系,认为王阳明心学体系的建立,有赖于其对“理”、“心”、“物”、“事”、“知”、“行”等语词不同于理学而赋予的新阐释。在“心即是理”这一心、理无二的前提下,确立了心所具有的统治地位。在确立我之为我的根基之后,通过“致良知”这一道德践履的方式,将现实生活的“物”与“事”联系起来,主张“知行合一”,从而完成了从个体内心向外在世界的过渡,也为具体实现修身齐家治国平天下的“外王”事业提供了一种可能。     

大学生物化学课程酶动力学教学之我见

酶动力学是大学生化课程教学的重要内容,旨在培养学生分析酶和配体相互作用的基本能力。随着生物医学体外研究技术的兴起,分析酶-配体相互作用将会成为研究者必备的基本技能,但是当前酶动力学的教学内容并不能达到这一目标。本文从科学研究实际出发,重点讨论现行酶动力学教学的不足,认为在该部分的教学中应加入动力学模型构建和非米氏动力学的内容。     

Effects on the photoresponse of calcium buffers and cyclic GMP incorporated into the cytoplasm of retinal rods

It is generally accepted that the light response in retinal rods involves a reduction of ionic permeability (predominantly to Na+) in the plasma membrane of the outer segment and that this is mediated by an internal messenger which diffuses between the disk and plasma membranes. There is controversy, however, over the identity of the diffusible substance; two alternative schemes have received widespread support (for review see refs 1,2). According to the 'calcium hypothesis', light stimulates the release into the cytoplasm of calcium, leading to the blockage of channels which are normally open in darkness, whereas based on the 'cyclic nucleotide hypothesis', cyclic GMP causes the opening of channels in the dark, but is hydrolysed by a light-activated phosphodiesterase. We report here effects of introducing calcium buffers and cyclic GMP into the rod cytoplasm by means of a patch pipette, which seem to be inconsistent with the calcium hypothesis.     

Type I iodothyronine deiodinase is a selenocysteine-containing enzyme.

Although thyroxine (3,5,3',5'-tetraiodothyronine, T4) is the principal secretory product of the vertebrate thyroid, its essential metabolic and developmental effects are all mediated by 3,5,3'-triiodothyronine (T3), which is produced from the prohormone by 5'-deiodination. The type-I iodothyronine deiodinase, a thiol-requiring propylthiouracil-sensitive oxidoreductase, is found mainly in liver and kidney and provides most of the circulating T3(1) but so far this enzyme has not been purified. Using expression cloning in the Xenopus oocyte, we have isolated a 2.1-kilobase complementary DNA for this deiodinase from a rat liver cDNA library. The kinetic properties of the protein expressed in transient assay systems, the tissue distribution of the messenger RNA, and its changes with thyroid status, all confirm its identity. We find that the mRNA for this enzyme contains a UGA codon for selenocysteine which is necessary for maximal enzyme activity. This explains why conversion of T4 to T3 is impaired in experimental selenium deficiency and identifies an essential role for this trace element in thyroid hormone action.     

大学新生和毕业生压抑感对比研究

在苏州定年级、四年级的文理科学生中保持性别比例适当地各抽取样本，采用《大学生压抑感调查问卷》进行问卷测试并进行ＳＰＳＳ统计检验。结果发现。苏州大学新生和毕业生群体压抑感程度属正常水平；压抑感来源因素按重要性排序为：社会环境因素、学校因素、个人因素和家庭因素；在社会环境因素和学校因素两个变量上体现出极显著的年级差异（Ｐ〈０．００１）。     

浅析英语头韵修辞格

头韵是英语中常见的修辞手法,它能赋予语言以音韵美和节奏美,能增强语言的表现力及感染力,因而经常被应用于各类文学作品及新闻报道、广告、习语、谚语等文体中。本文对头韵的表现形式及其应用范围进行了探讨。     

语言僵化现象分析

语言僵化是二语习得中的一个普遍现象。探讨僵化的起因对弄清语言习得的内部过程具有重要的意义。本文借助第二语言习得的相关理论，从年龄、社会文化环境、母语干扰、反馈性质四个方面分析语言僵化产生的原因，并结合实际，提出防止僵化的几点建议。     

禁止字方法在元胞自动机中的一个应用

给出了使用禁止字理论、计算机搜索和符号动力学研究初等元胞自动机演化语言的一种方法，并且使用该方法得到了27号初等元胞自动机演化语言在数学上的精确描述．     

An excitable gene regulatory circuit induces transient cellular differentiation

Certain types of cellular differentiation are probabilistic and transient. In such systems individual cells can switch to an alternative state and, after some time, switch back again. In Bacillus subtilis, competence is an example of such a transiently differentiated state associated with the capability for DNA uptake from the environment. Individual genes and proteins underlying differentiation into the competent state have been identified, but it has been unclear how these genes interact dynamically in individual cells to control both spontaneous entry into competence and return to vegetative growth. Here we show that this behaviour can be understood in terms of excitability in the underlying genetic circuit. Using quantitative fluorescence time-lapse microscopy, we directly observed the activities of multiple circuit components simultaneously in individual cells, and analysed the resulting data in terms of a mathematical model. We find that an excitable core module containing positive and negative feedback loops can explain both entry into, and exit from, the competent state. We further tested this model by analysing initiation in sister cells, and by re-engineering the gene circuit to specifically block exit. Excitable dynamics driven by noise naturally generate stochastic and transient responses, thereby providing an ideal mechanism for competence regulation.     

Angiotensin-converting enzyme 2 is an essential regulator of heart function

Cardiovascular diseases are predicted to be the most common cause of death worldwide by 2020. Here we show that angiotensin-converting enzyme 2 (ace2) maps to a defined quantitative trait locus (QTL) on the X chromosome in three different rat models of hypertension. In all hypertensive rat strains, ACE2 messenger RNA and protein expression were markedly reduced, suggesting that ace2 is a candidate gene for this QTL. Targeted disruption of ACE2 in mice results in a severe cardiac contractility defect, increased angiotensin II levels, and upregulation of hypoxia-induced genes in the heart. Genetic ablation of ACE on an ACE2 mutant background completely rescues the cardiac phenotype. But disruption of ACER, a Drosophila ACE2 homologue, results in a severe defect of heart morphogenesis. These genetic data for ACE2 show that it is an essential regulator of heart function in vivo.     

Epidermal growth factor receptor is a cellular receptor for human cytomegalovirus

Human cytomegalovirus (HCMV) is a widespread opportunistic herpesvirus that causes severe and fatal diseases in immune-compromised individuals, including organ transplant recipients and individuals with AIDS. It is also a leading cause of virus-associated birth defects and is associated with atherosclerosis and coronary restenosis. HCMV initiates infection and intracellular signalling by binding to its cognate cellular receptors and by activating several signalling pathways including those mediated by mitogen-activated protein kinase, phosphatidylinositol-3-OH kinase, interferons, and G proteins. But a cellular receptor responsible for viral entry and HCMV-induced signalling has yet to be identified. Here we show that HCMV infects cells by interacting with epidermal growth factor receptor (EGFR) and inducing signalling. Transfecting EGFR-negative cells with an EGFR complementary DNA renders non-susceptible cells susceptible to HCMV. Ligand displacement and crosslinking analyses show that HCMV interacts with EGFR through gB, its principal envelope glycoprotein. gB preferentially binds EGFR and EGFR-ErbB3 oligomeric molecules in Chinese hamster ovary cells transfected with erbB family cDNAs. Taken together, these data indicate that EGFR is a necessary component for HCMV-triggered signalling and viral entry.     

Structural insight into antibiotic fosfomycin biosynthesis by a mononuclear iron enzyme

The biosynthetic pathway of the clinically important antibiotic fosfomycin uses enzymes that catalyse reactions without precedent in biology. Among these is hydroxypropylphosphonic acid epoxidase, which represents a new subfamily of non-haem mononuclear iron enzymes. Here we present six X-ray structures of this enzyme: the apoenzyme at 2.0 A resolution; a native Fe(II)-bound form at 2.4 A resolution; a tris(hydroxymethyl)aminomethane-Co(II)-enzyme complex structure at 1.8 A resolution; a substrate-Co(II)-enzyme complex structure at 2.5 A resolution; and two substrate-Fe(II)-enzyme complexes at 2.1 and 2.3 A resolution. These structural data lead us to suggest how this enzyme is able to recognize and respond to its substrate with a conformational change that protects the radical-based intermediates formed during catalysis. Comparisons with other family members suggest why substrate binding is able to prime iron for dioxygen binding in the absence of alpha-ketoglutarate (a co-substrate required by many mononuclear iron enzymes), and how the unique epoxidation reaction of hydroxypropylphosphonic acid epoxidase may occur.     

养成教育透析

根据对未来人才素质的一般要求,论述对学生进行养成教育的必要性及其理论基础,提出学生在学校生活中应当养成的几种习惯,并从应用强化、内在动机激发、氛围熏陶、实践训练四个方面论述了养成教育的途径与方法。     

软件过程RUP的探讨

文章介绍了Rational统一过程(RUP)的主要内容,包括开发模型、核心工作流和迭代过程等.通过与传统项目组织的比较给出了RUP的优势同时也提出了不足之处.