Peroxynitrite-mediated tyrosine nitration catalyzed by superoxide dismutase.

Peroxynitrite (ONOO-), the reaction product of superoxide (O2-) and nitric oxide (NO), may be a major cytotoxic agent produced during inflammation, sepsis, and ischemia/reperfusion. Bovine Cu,Zn superoxide dismutase reacted with peroxynitrite to form a stable yellow protein-bound adduct identified as nitrotyrosine. The uv-visible spectrum of the peroxynitrite-modified superoxide dismutase was highly pH dependent, exhibiting a peak at 438 nm at alkaline pH that shifts to 356 nm at acidic pH. An equivalent uv-visible spectrum was obtained by Cu,Zn superoxide dismutase treated with tetranitromethane. The Raman spectrum of authentic nitrotyrosine was contained in the spectrum of peroxynitrite-modified Cu,Zn superoxide dismutase. The reaction was specific for peroxynitrite because no significant amounts of nitrotyrosine were formed with nitric oxide (NO), nitrogen dioxide (NO2), nitrite (NO2-), or nitrate (NO3-). Removal of the copper from the Cu,Zn superoxide dismutase prevented formation of nitrotyrosine by peroxynitrite. The mechanism appears to involve peroxynitrite initially reacting with the active site copper to form an intermediate with the reactivity of nitronium ion (NO2+), which then nitrates tyrosine on a second molecule of superoxide dismutase. In the absence of exogenous phenolics, the rate of nitration of tyrosine followed second-order kinetics with respect to Cu,Zn superoxide dismutase concentration, proceeding at a rate of 1.0 +/- 0.1 M-1.s-1. Peroxynitrite-mediated nitration of tyrosine was also observed with the Mn and Fe superoxide dismutases as well as other copper-containing proteins.     

Bactericidal activity of peroxynitrite.

Peroxynitrite is a strong oxidant formed by macrophages and potentially by other cells that produce nitric oxide and superoxide. Peroxynitrite was highly bactericidal, killing Escherichia coli in direct proportion to its concentration with an LD50 of 250 microM at 37 degrees C in potassium phosphate, pH 7.4. The apparent bactericidal activity of a given concentration peroxynitrite at acidic pH was less than that at neutral and alkaline pH. However, after taking the rapid pH-dependent decomposition of peroxynitrite into account, the rate of the killing was not significantly different at pH 5 compared to pH 7.4. Metal chelators did not decrease peroxynitrite-mediated killing, indicating that exogenous transition metals were not required for toxicity. The hydroxyl radical scavengers mannitol, ethanol, and benzoate did not significantly affect toxicity while dimethyl sulfoxide enhanced peroxynitrite-mediated killing. Dimethyl sulfoxide is a more efficient hydroxyl radical scavenger than the other three scavengers and increased the formation of nitrogen dioxide from peroxynitrite. In the presence of 100 mM dimethyl sulfoxide, 60.0 +/- 0.3 microM nitrogen dioxide was formed from 250 microM peroxynitrite as compared to 2.0 +/- 0.1 microM in buffer alone. Thus, formation of nitrogen dioxide may have enhanced the toxicity of peroxynitrite decomposing in the presence of dimethyl sulfoxide.     

Molecular thermodynamic model to predict the alpha-helical secondary structure of polypeptide chains in solution.

The native state of a protein molecule in aqueous solutions represents one of the lowest states of Gibbs energy [Anfinsen, C.B. (1973) Science 181, 223-230]. Much progress has been made about the rules of protein folding [King, J. (1989) Chem. Eng. News 67, 32-54] and the dominant forces in protein folding [Dill, K.A. (1990) Biochemistry 29, 7133-7155]. However, the quantitative contributions of different Gibbs energy terms to protein stability remains a controversial issue [Moult, J., & Unger, R. (1991) Biochemistry 30, 3816-3824]. A molecular thermodynamic model has been proposed for the Gibbs energy of folding a residue in aqueous homopolypeptides from a random-coiled state to either the alpha-helix state or the beta-sheet state [Chen, C.-C., Zhu, Y., King, J.A., & Evans, L.B. (1992) Biopolymers 32, 1375-1392]. In this work, we present a generalization of the molecular thermodynamic model for the Gibbs energy of folding natural and synthetic heteropolypeptides from random-coiled conformations into alpha-helical conformations. The generalized model incorporates the intrinsic folding potential due to residue-solvent interactions, the cooperative folding effect due to residue-residue interactions, and the location and length of alpha-helices. The utility of the model was demonstrated by examining the stability of alpha-helical conformations of a number of natural polypeptides including C-peptide (residues 1-13) and S-peptide (residues 1-20) of RNase A (bovine pancreatic ribonuclease A), the P alpha fragment in BPTI (bovine pancreatic trypsin inhibitor), and synthetic polypeptides (the copolymers of different amino acid residues) including alanine-based peptides (16 or 17 residues long) in water. The computed Gibbs energies correspond well with the experimental data on helicity. The results also accounted for the effects of amino acid substitution and temperature on the stability of alpha-helical conformations of the test polypeptides.     

元江干热河谷肉质多利灌丛的研究

以内质多刺植物霸王鞭(Euphorbia royleana)和仙人掌(Opuntia monacantha)为特征的具有荒漠植被景观的元江干热河谷肉质多刺灌丛是一种特殊的次生植被,是在近代原生植被的强烈破坏下,栽培逸生的霸王鞭和仙人掌在局部特别千热土薄多石之处发展而形成的。该群落外貌和结构特殊,可初步定为一个群丛,下分两个亚群丛。在种类组成上,该群落与热带亚洲干早植物区系联系密切,在区系起源上具有古南大陆残余背景,在群落形成和发展上又与人为活动相联系。     

中国大白蚁亚科壤白蚁新属新种（等翅目：白蚁科）

壤白蚁属Parahy potermes Zhu et Huang,新属 模式种:曼允壤白蚁Parahy potermes manyunensis,新种。 属征:兵蚁头近卵圆形,头背面被毛稀少,两侧缘于触角前骤然狭缩,头中部最宽,后缘宽圆,头背面中部明显隆起;左上颚内缘中部第1缘齿上方具2—3枚小齿。 比较与讨论:本新属与地白蚁属Hypotermes Holmgren较接近。但Hypotermes头两侧缘触角前不呈狭缩状;左上颚第1缘齿上方不具锯齿状小齿;头背面中部呈弧状隆起。     

Efficient translocation of positively charged residues of M13 procoat protein across the membrane excludes electrophoresis as the primary force for membrane insertion.

The coat protein of bacteriophage M13 is inserted into the Escherichia coli plasma membrane as a precursor protein, termed procoat, with a typical leader peptide of 23 amino acid residues. Its membrane insertion requires the electrochemical potential but not the cellular components SecA and SecY. Since the electrochemical gradients result in the periplasmic side of the membrane being positively charged, the membrane potential could contribute to the transfer of the negatively charged central region of procoat across the membrane. Here we demonstrate that the central domain following the leader peptide can be translocated across the membrane even when the net charge of the region is changed from -3 to +3. This rules out an electrophoresis-like insertion mechanism for procoat. We also show that the sec independence of procoat insertion is linked to the presence of the second apolar domain. The deletion of most of the second apolar domain from a procoat fusion protein results in sec dependent membrane insertion of the hybrid protein. Moreover, like other proteins that require the sec genes, translocation of this sec dependent procoat protein is inhibited when positively charged residues are introduced after the leader peptide. Loop models involving one or two hydrophobic regions are presented that account for the differences in tolerance of positively charged residues.     

急性缺氧性缺氧时心脏功能的改变

F_(IO_2)(吸入气氧浓度)为12.35、9.87及7.7l％,分别吸入10、8及5min时,心功能呈代偿性增强改变。F_(IO_2)为9.37％、吸入20min时心功能的变化趋势与9.87％8min时仍基本相同。继发性缺二氧化碳对缺氧引起的心功能代偿性增强,在一定程度上起抵消作用。F_(IO_2)为9.87％时的缺氧程度约相当于18km高空加压供氧总压值为15.3kPa(115mmHg)时的缺氧。单纯从缺氧因素考虑,将总压值由常用的17.3kPa(130mmHg)降低为15.3kPa是可允许的。     

串叶松香草的核型研究

串叶松香草Silphiura perfoliatum L.系菊科(Compositae)松香草属(SilphiumL.)多年生宿根草本植物,原产北美洲。1979年由中国科学院植物研究所北京植物园首次从朝鲜引进我国,1980年引种我所栽培,通过几年的试验观察表明:串叶松香草是一种高产、质优、适应性强的饲料作物,近年来,我省广泛发展和应用。据文献报     

草莓花药培养获得无病毒植株的技术研究

以花粉发育为单核期的花药接种,在MS附加IAA 4ppm、K 2ppm、BA 2ppm的培养基上诱导愈伤组织,并可直接分化出“沙尔普斯”、“红岗利德”、“春香”3个品种的花药植株。稍加调整附加激素成分和浓度,可在“索非亚”、“宝交早生”、“戈雷拉”、“红衣”、“丽红”等品种的花药上直接经愈伤组织分化出植株。其中有“沙尔普斯”、“红岗利德”、“春香”、“宝交早生”、“索非亚”等5个品种的花药植株经过病毒检测确认不带SMoV、SCrV、SMYEV和SVBV4种病毒。对无病毒植株进行了田间对比试验,植株生长势和果实产量都明显超过对照品种。     

冬虫夏草多糖的分子结构与免疫活性

 冬虫夏草多糖(在本文中名为CS-81002)是由冬虫夏草菌Cordyceps sinensis(Berk)Sacc在人工发酵条件下产生的胞外多糖。用凝胶过滤法测出CS-81002的分子量Mr=43kD。CS-81002的单糖组成为Man:Gal:Glc=10.3:3.6:1。甲基化分析和部份酸水解结果表明,CS-81002是多分支的杂多糖,由→6)-Manp-(1→形成主链,大约每10个主链Man残基中,有6个在C3位上被取代(即形成→3,6)-Manp-(1→分支),有4个在位C2上被取代(即形成→2,6-Manp-(1→分支),从而形成侧链。主链中还有少许未被取代的Man残基。侧链则由→3-)-Galf-(1→,→4)-Glcf-(1→,→4)-Manp-(1→和→2)-Manp-(1→组成。位于非还原末端的,则三种单糖残基都有。CS-81002在5mg/kg体重×12剂量条件下,对正常的昆明小鼠腹腔巨噬细胞吞噬功能有显著促进作用。在同样剂量条件下,对正常LACA小鼠脾脏溶血斑形成细胞(PFC)对绵羊红细胞的溶血作用无显著影响。不同程度的部份酸水解可使CS-81002的分子量下降,分支减少,并且对巨噬细胞吞噬功能的促进作用亦有下降趋势。在所得到的各个部份酸水解级分(分子量分别为41000,40000,32000,16000和12000)中,分子量为12000的级分对巨噬细胞吞噬功能无促进作用。