Myosin subfragment-1 is sufficient to move actin filaments in vitro

The rotating crossbridge model for muscle contraction proposes that force is produced by a change in angle of the crossbridge between the overlapping thick and thin filaments. Myosin, the major component of the thick filament, is comprised of two heavy chains and two pairs of light chains. Together they form two globular heads, which give rise to the crossbridge in muscle, and a coiled-coil rod, which forms the shaft of the thick filament. The isolated head fragment, subfragment-1 (S1), contains the ATPase and actin-binding activities of myosin (Fig. 1). Although S1 seems to have the requisite enzymatic activity, direct evidence that S1 is sufficient to drive actin movement has been lacking. It has long been recognized that in vitro movement assays are an important approach for identifying the elements in muscle responsible for force generation. Hynes et al. showed that beads coated with heavy meromyosin (HMM), a soluble proteolytic fragment of myosin consisting of a part of the rod and the two heads, can move on Nitella actin filaments. Using the myosin-coated surface assay of Kron and Spudich, Harada et al. showed that single-headed myosin filaments bound to glass support movement of actin at nearly the same speed as intact myosin filaments. These studies show that the terminal portion of the rod and the two-headed nature of myosin are not required for movement. To restrict the region responsible for movement further, we have modified the myosin-coated surface assay by replacing the glass surface with a nitrocellulose film. Here we report that myosin filaments, soluble myosin, HMM or S1, when bound to a nitrocellulose film, support actin sliding movement (Fig. 2). That S1 is sufficient to cause sliding movement of actin filaments in vitro gives strong support to models of contraction that place the site of active movement in muscle within the myosin head.     

Expression and functional characterization of artificial mutants of interleukin-2 receptor

The physiological proliferation of T lymphocytes (T cells) requires interaction between the humoral growth factor, interleukin 2 (IL-2) and its cell-surface receptor. Studies of IL-2 binding to the IL-2 receptor (IL-2R) on T cells have revealed that there are two distinct species of IL-2R, one with high and one with low affinity. Isolation and characterization of cDNA for the human IL-2R made it possible to deduce the complete primary sequence (251 residues) of the receptor protein. However, expression of IL-2R alone is not sufficient for either growth signal transduction or high-affinity site formation: another lymphocyte-specific molecule called converter seems to be required for the biological activity of IL-2R. We found that the converter did not form a stable complex with IL-2R unless the receptor bound the ligand (the 'affinity conversion' model). To discover which are the functionally important parts of the human IL-2R we have constructed artificial mutant cDNAs encoding the receptor. The mutant receptors produced from them had deletions or substitutions in the cytoplasmic region (13 residues), the transmembrane region (19 residues) or the carboxy-terminal portion of the extracellular region (219 residues). All were active in growth signal transduction, efficient internalization and high-affinity site formation in two mouse T-cell lines, suggesting that the extracellular region of IL-2R and the converter may be responsible for growth signal transduction.     

A new immunomodulating compound (AS-101) with potential therapeutic application

There has been interest in the potential of synthetic compounds to modify immune responses by imitation of cytokine action. Direct administration of interleukin 2 (IL-2) in conjunction with adoptive transfer of lymphokine activated killer cells has been used in the treatment of cancer, but there are toxic effects resulting from the high doses of IL-2 required. We have developed a new synthetic compound, ammonium tri-chloro(dioxoethylene-O,O'-)tellurate (AS-101), which has immunomodulating properties and minimal toxicity. The effects of AS-101 on the activation and function of immunocompetent cells have been assessed. We have found that AS-101 induces proliferation and IL-2 production by human lymphocytes in vitro, and enhances the production of IL-2 and colony-stimulating factor by mouse spleen cells. Splenocytes of BALB/c mice injected with AS-101 increased production of IL-2 and CSF in vitro in the presence of mitogen. Mononuclear cells of normal donors acquired responsiveness to recombinant IL-2 and bound monoclonal antibody to IL-2 receptor after incubation with AS-101. Splenocytes of mice treated in vivo with AS-101 expressed high levels of IL-2 receptor. The stimulation of lymphocytes by AS-101 apparently involves an increase in intracellular free calcium. AS-101 administered systemically to mice mediated antitumour effects which could be attributable to its immunomodulatory properties. In addition, AS-101 could directly enhance the ratio of OKT4 to OKT8-positive cells in cultured mononuclear cells from AIDS (acquired immune deficiency syndrome) patients. These results indicate that AS-101 is potentially useful in the treatment of clinical conditions involving immunosuppression.     

HIV F/3' orf encodes a phosphorylated GTP-binding protein resembling an oncogene product

Apart from the retroviral gag, pol and env the HIV genome contains the F (3' orf) gene which encodes a polypeptide of 206 amino acids which is myristylated at the N-terminal and whose function is unknown. We have expressed the F gene in Escherichia coli and from a recombinant vaccinia virus, VVTGfHIV. The F-protein produced in VVTGfHIV-infected mammalian cells is myristilated, and is phosphorylated by protein kinase C at a residue close to the N-terminus like pp60-src (ref. 5). Purified bacterial F-protein also shows the GTPase, autophosphorylation and GTP-binding activities reported for the ras gene product. Furthermore, we show that expression of F in a CD4+ cell line down-regulates the CD4(T4) antigen. These results suggest that F is important in the pathophysiology of AIDS (acquired immune deficiency syndrome).     

Kinetics of smooth and skeletal muscle activation by laser pulse photolysis of caged inositol 1,4,5-trisphosphate

Inositol 1,4,5-trisphosphate (InsP3) can stimulate skinned smooth and skeletal muscle to contract by initiating Ca2+ release from the sarcoplasmic reticulum. Whether this process is an integral component of the in vivo muscle activation mechanism was tested by releasing InsP3 rapidly within skinned muscle fibers of rabbit main pulmonary artery and frog semitendinosus. InsP3 was liberated on laser pulse photolysis of a photolabile but biologically inactive precursor of InsP3 termed caged InsP3. Caged InsP3 is a mixture of compounds in which InsP3 is esterified with 1(2-nitrophenyl)diazoethane (probably at the P4- or P5-position). Photochemical release of InsP3 induced a full contraction in both muscles at physiological free Mg2+ concentrations, but only in the smooth muscle were the InsP3 concentration (0.5 microM) and the activation rate compatible with the in vivo physiological response. Endogenous InsP3-specific phosphatase activity was present in smooth muscle and had about 35-fold greater activity than that in the skeletal-muscle preparation. Caged InsP3 was not susceptible to phosphatases in either preparation.     

Glioma cell activation by Alzheimer's peptide Abeta1-42, alpha1-antichymotrypsin,and their mixture

We compared the effects ofAlzheimer's peptide (Abeta1-42), a,-antichymotrypsin (ACT) and an ACT/Abeta1-42 mixture on human glioma DK-MG cells. The solution of Abeta (5 microM) formed by 2-h incubation at room temperature induced tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 levels by 55 and 45%, respectively, and increased gelatinase B activity by 67%, while exposure of cells to the ACT/Abeta1-42 mixture (1:10 molar ratio ACT: Abeta1-42) under the same experimental conditions showed no effect on IL-6 levels or gelatinase B activity, but strongly induced TNF-alpha (by 190%), compared to the controls. Stimulation of the cells with Abeta1-42 alone, but not with ACT, increased by about 20% low-density lipoprotein (LDL) uptake and mRNA levels for LDL receptor and HMG-CoA reductase, while the ACT/Abeta1-42 mixture significantly increased LDL uptake (by 50%), up-regulated mRNA levels for LDL receptor and HMG-CoA reductase by 48 and 63%, respectively, and increased lipid accumulation by about 20-fold. These data suggest a possible new role for Abeta in Alzheimer's disease through its interaction with the inflammatory reactant, ACT.     

一种用于结构动态过程数值模拟的广义有限元法

提出了一种能同时处理连续体和离散体动态过程的有限元法. 该法通过构造接触力模型, 将传统的离散元当做标准的一节点有限单元来看待. 新构造的一节点单元与常规有限单元具有同样物理特征, 包括应力和应变. 从而, 将离散元算法与有限元算法紧密结合在一起, 形成了统一的、与现有有限元系统兼容的广义有限元计算模型. 这种模型不仅简化了计算过程, 还可最大限度地发挥现有有限元代码的功能. 数值算例表明, 新方法可以更加有效地模拟大量离散体与连续体相互作用的复杂动力学过程.     

青藏高原北羌塘新生代火山岩黑云母地球化学及其岩石学意义

分析了北羌塘半岛湖新第三纪玻基粗面安山岩中黑云母的常量、微量及稀土元素特征.结果表明,黑云母均属钛铁黑云母类,富集大离子亲石元素Ba以及Sc,Ti,V,Cr,Co,Ni等铁族元素,而相对亏损Th,U,Pb等亲石元素.轻稀土强烈富集,轻重稀土分异显著,但Eu亏损并不严重,暗示原始岩浆来源于一个基性岩质的、相当于榴辉岩矿物相(斜长石相缺失)的源区类型.     

广西产眼镜王蛇毒α-神经毒素基因的分子克隆及序列分析

为获得眼镜王蛇（Ophiophagus hannah，简称Oh）蛇毒α－神经毒素（α-NT）的基因序列，依据眼镜蛇科不同毒蛇种类来源的α－NT基因有较高的同源性，设计1对上下游引物，为克服引物带来模糊扩增，在蛋白编码部分再设计1对上下游特异引物，用Nacleospin RNA Kit法从3条活眼镜王蛇毒腺中提取mRNA，以3′端引物合成的cDNA作为模板进行PCR扩增反应，测定产物的核苷酸序列，得到全长474bp的眼镜王蛇cDNA基因核苷酸序列。该核苷酸序列的信号肽与眼镜蛇树属Pseudonnaja textilis(Pt)、海蛇Laticauda semifasciata(Ls)100%同源，与眼镜蛇南洋亚种Naja sputatrix (Ns)、银环蛇（Bungarus multicinctus)(Bm)96.8%同源；蛋白密码部分有83．3％与Ns、79．2％与Pt、76．4％与Ls、74．1％与Bm同源。信号肽后紧接着的72个氨基酸有90．3％与已发现的眼镜王蛇毒长链α-NT Toxin a同源，大约有73．6％与Toxin b、69．7％与Oh-4、66．7％与Oh-5、56．9％与Oh-6A和6B同源，并与α－银环蛇毒素54．2％同源。说明新发现的眼镜王蛇cDNA是一条长链α-NT基因。