Subunit interaction in extracellular superoxide dismutase: effects of mutations in the N-terminal domain.

Human extracellular superoxide dismutase (hEC-SOD) is a secreted tetrameric protein involved in protection against oxygen free radicals. Because EC-SOD is too large a protein for structural determination by multidimensional NMR, and attempts to crystallize the protein for X-ray structural determination have failed, the three-dimensional structure of hEC-SOD is unknown. This means that alternative strategies for structural studies are needed. The N-terminal domain of EC-SOD has already been studied using the fusion protein FusNN, comprised of the 49 N-terminal amino acids from hEC-SOD fused to human carbonic anhydrase (HCAII). The N-terminal domain in this fusion protein forms a well-defined three-dimensional structure, which probably contains alpha-helical elements and is responsible for the tetramerization of the protein. In this work, we have extended the studies, using site-directed mutagenesis in combination with size-exclusion chromatography, CD, and fluorescence spectroscopy, to investigate the nature of the tetrameric interaction. Our results show that the hydrophobic side of a predicted amphiphatic alpha-helix (formed by residues 14-32) in the N-terminal domain is essential for the subunit interaction.     

Synergistic effects of cellulolytic and pectinolytic enzymes in degrading sugar beet pulp

Three cellulases, one hemicellulase and three pectinases were used, separately or in binary and ternary combinations, to hydrolyze dried beet-pulp, a by-product of the sugar industry. By IE-HPLC the compositions and concentrations of the sugars released were determined. The results obtained by enzymatic saccharification were compared to those obtained by acid hydrolysis. The synergistic action of cellulolytic and pectinolytic enzymes in release of total monosaccharides, and of glucose, arabinose and galacturonic acid was also studied. The combination of cellulase, hemicellulase and pectinase, commercially available, was as effective in degrading the beet pulp as the acid hydrolysis. Pectinase appeared to be the most important enzyme, since by hydrolyzing the pectic surface of the lignocellulosic substrate, it favoured the degradation of cellulose and hemicellulose by the respective enzymes.     

内蒙古察哈尔丘陵啮齿动物种群数量的波动和演替

根据内蒙古自治区正镶白旗乌宁巴图苏木９７４－１９９３年随啮齿动物密度监测资料进行分析,得到如下结果。共捕啮齿动物１３种,其中达乌尔黄鼠为优势种（６７．８５％）、一趾鼠为次优势种（１０．１６％）,长爪沙鼠、布氏田鼠、达乌尔鼠兔为常见种,余为少见种。黄鼠密度与个体数呈正相关（Ｐ〈０．０００１）、五趾跳鼠与个体数、黄鼠密度呈负相关（Ｐ〈０．００１）。个体数与黄鼠、五趾跳鼠密度的回归模型为：（个体数）＝１     

人微小纤溶酶原基因的克隆和表达

用PCR方法扩增人微小纤溶酶原(Microplasmingen,mPlg)基因,再与表达载体重组．构造mPlg原核表达质粒并转化大肠杆菌。阳性克隆pSSE-mPlg经温度诱导表达,SDS-PAGE等方法证明表达产物的分子量约为29kDa。占全菌总蛋白的24％左右,并在菌内形成包涵体。经半胱氨酸再氧化法和空气氧化法复性。表达产物r-mPlg经SK作用后显示纤溶活性。同时对蛋白质浓度、复性时间等因素对复性的影响进行了初步探讨。     

谷胱甘肽硫转移酶基因表达的调控

催化内源性或外源性亲电子化合物与谷胱甘肽(GSH)结合的谷胱甘肽硫转移酶(GST)超基因家族是一族解毒功能蛋白.其基因的表达通过不同的机制受多种物质的调控.根据最近文献资料,对调控谷胱甘肽硫转移酶基因表达的基因结构、调控机制及氧化应激对谷胱甘肽硫转移酶基因表达的调控作用等作一简要综述.     

EB病毒BNLF-1基因的分子生物学研究进展

位于EB病毒基因组U₅-TR区内的BNLF-1基因,其转译产物为潜伏膜蛋白(latent membrane protein1, LMP-1),由于LMP-1可以导致细胞转化并在EB病毒致癌过程中具有重要作用,因而成为近年来EB病毒分子生物学及相关肿瘤如人鼻咽癌、伯基特淋巴瘤、何杰金氏病等疾病病因发病学研究的热点,并取得了一批有重要意义的成果,文章从BNLF-1的基因结构及表达调控, LMP蛋白的结构及生化功能, LMP-1的生物学功能和LMP-1研究进行评述.     

腺苷酸激酶基因在大肠杆菌中的可溶性高表达

报道了鸡肌腺苷酸激酶基因的克隆和在温控启动子P_RP_L调控下在大肠杆菌中的可溶性高效表达.SDS-PAGE分析表明,鸡肌腺苷酸激酶的含量可占大肠杆菌细胞总蛋白含量的38％.利用Johnson等的干冰/乙醇-冰水浴反复冻融法,可将此重组蛋白进行富集,纯度可达85％以上.鸡肌腺苷酸激酶可与抗兔肌腺苷酸激酶单克隆抗体产生强的交叉反应.     

GI双突变体GIK253RA198C的构建及其性质分析

以双引物法对葡萄糖异构酶（GI）基因进行定点突变,将突变体基因于大肠杆菌中表达,获得了GI双点突变体GIK253RA198C.研究K253R和A198C双点突变对GI的结构和性质的作用,结果表明GIK253RA198C的热稳定性明显下降,最适反应温度降低5℃.文章从结构和机制上解释了为何同是K253R突变,对SM33 GI和密苏里游动放线菌GI的热稳定性产生不同的影响,认为这是由于Lys253在两种GI结构的位置上存在微小差异,从而使引入的Arg对亚基间的相互作用产生了相反效应所引起.     

International study on Artemia. LIV. Morphological study of Artemia with emphasis to Old World strains. II. Parthenogenetic populations

Eleven morphometric and one meristic character in 15 parthenogeneticArtemia populations have been studied by using discriminant andcluster analysis as well as scanning electron microscopy.Discriminant analysis revealed five main groups of morphologicalpatterns: (i) the coastal Chinese populations together with apopulation from Kazakhstan, (ii) the inland Chinese salt lakepopulations, (iii) the Greek populations, (iv) one African populationfrom Namibia and (v) a Chinese population from Xuyu (Jiangsuprovince). Cluster analysis was not always in agreement withdiscriminant analysis and these results are discussed.