Polypeptide translocation machinery of the yeast endoplasmic reticulum

Proteins enter the secretory pathway by two general routes. In one, the complete polypeptide is made in the cytoplasm and held in an incompletely folded state by chaperoning adenosine triphosphatases (ATPases) such as hsp70. InSaccharomyces cerevisiae, fully synthesized secretory precursors engage the endoplasmic reticulum (ER) membrane by interaction with a set of Sec proteins comprising the polypeptide translocation apparatus (Sec61p, Sec62p, Sec63p, Sec71p, Sec72p). Productive interaction requires displacement of hsp70 from the precursor, a reaction that is facilitated by Ydj1p, a homologue of theEscherichia coli DnaJ protein. Both DnaJ and Ydj1p regulate chaperone activity by stimulating the ATPase activity of their respective hsp70 partners (E. coli DnaK andS. cerevisiae Ssa1p, resepectively). In the ER lumen, another hsp70 chaperone, BiP, binds ATP and interacts with the ER membrane via its contact with a peptide loop of Sec63p. This loop represents yet another DnaJ homologue in that it contains a region of 70 residue similarity to the J box, the most conserved region of the DnaJ family of proteins. In the presence of ATP, under conditions in which BiP can bind to Sec63p, the secretory precursor passes from the cytosol into the lumen through a membrane channel formed by Sec61 p. A second route to the membrane pore that is used by many other secretory precursors, particularly in mammalian cells, requires that the polypeptide engage the ER membrane as the nascent chain emerges from the ribosome. Such cotranslational translocation bypasses the need for certain Sec proteins, instead utilizing an alternate set of cytosolic and membrane factors that allows the nascent chain to be inserted directly into the Sec61p channel.     

Some citrus chitinases also possess chitosanase activities

Several acidic chitinase and chitosanase isoforms were found in 4-week-old nonembryogenic sweet orange (Valencia [Citrus sinensis (L.) Osbeck]) callus tissue. Two isoforms (designated A1-CF1 and A1-CF2) were purified to homogeneity using HPLC size exclusion, anion exchange, and chromatofocusing techniques. Both hydrolase isoforms exhibited activity with either colloidal chitin or solubilized shrimp shell chitosan. Specific activities for the purified isoforms could not be calculated because of the lack of protein and contamination of ampholytes. However, the specific activities for chitinase and chitosanase after anion exchange were respectively 404 nmol GlcNAc per min per mg protein and 2,475 nmol GlcN per min per mg protein. The M_r for both enzymes was 30,500. The homogeneous proteins cross-reacted in western blots with antiserum against a basic class I potato leaf chitinase.     

黎曼近似解模型在太湖藻类浓度场求解中的应用

利用太湖常规监测点的监测资料，在黎曼近似解模型的基础上建立了太湖二维藻类生长模型，该模型采用有限体积法及黎曼近似解对二维水流水质方程组逐时段、逐单元进行求解，将每个时段各个单元ρ(TN)及ρ(TP)的模拟值传递到藻类的生长项，从而模拟出藻类的生长过程，率定验证结果表明，该模型能较好地模拟藻类的生长过程，并能对太湖水体富营养化进行预测。     

邻苯二甲酸酯对海洋藻类的致毒效应

采用评价化学药品对藻类毒性的标准方法，对邻苯二甲酸醋与海洋藻类的相互影响进行探讨．通过对邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙醋(DEP)、邻苯二甲酸二丁醋(DBP)海洋藻类的致毒试验，分别得出此3种物质对三角褐指藻、盐藻、等边金藻、中肋骨条藻48h、96h的半致死浓度，探讨了上述几种海洋藻类对DMP、DEP、DBP的忍受限度．     

兰州北山生物结皮中陆生藻种类组成与群落结构

通过对沙井驿、刘家堡、九州台、白塔山、小牛圈沟等样点采集的生物结皮样的培养和鉴定 ,研究了兰州市北山生物结皮中陆生藻种类组成及其群落结构 .结果发现 ,该地陆生藻共计 5 3种 ,其中蓝藻 34种 ,绿藻 7种 ,硅藻10种 ,裸藻 2种 .蓝藻中以丝状种类占优势 (6 5 % ) ,绿藻中仍以球状种类居多 (5 7% ) ,但也有不少丝状个体(43% ) .黄土结皮以非洲席藻为第一优势种 ,石崖表具鞘微鞘藻占绝对优势 ,人工草丛中小球藻最丰富 ;种类数在砾质黄土中最多 (2 3) ,黄粘土中最少 (16 ) .     

二甲苯蓝FF与蛋白质相互作用的分光光度研究

在pH1 7～2 8的弱酸性介质中,二甲苯蓝FF与牛血清蛋白、人血清蛋白、卵白蛋白、α 糜蛋白酶等作用形成结合产物时将导致吸收光谱发生变化,在390nm处产生明显的褪色作用,而在560nm附近吸光度增强,其ΔA值均与蛋白浓度成正比,根据蛋白质的不同分别在0～60mg/L或0～80mg/L范围内符合Beer定律,不同蛋白质的表观摩尔吸光系数在2 8×105至1 3×106之间.据此,建立了一种测定蛋白质的双波长叠加分析法.该法应用于血清蛋白样品中总蛋白质的质量分析,回收率在98 7%～102 9%范围内.     

视黄醇结合蛋白基因的研究发展

视黄醇结合蛋白(Retinol-Binding Proteins，RBP)是一类维生素A的运载蛋白，参与血清和细胞内视黄醇／酸的转运，是疏水小分子结合蛋白家族的成员。RBP主要在肝脏中合成并释放入血液进而进入各种组织，通过与视黄醇、前白蛋白及细胞表面受体相互作用，在维生素A的储存、代谢、转运到周围靶器官中具有重要功能。细胞内视黄醇结合蛋白则主要在细胞内发挥类似作用。本文主要就血清及细胞内视黄醇结合蛋白的基因结构、作用机理、发育性表达、组织定位及染色体定位、对动物繁殖性能和胚胎发育的影响等方面进行综述。     

动物血液学的比较研究 Ⅱ．几种脊椎动物的血象、血清蛋白和血液流变学的观察

本文报导了虎纹蛙、黑眶蟾蜍的血象、血清蛋白，中国雨蛙的白细胞分类计数和罗非鱼、家鸽、家兔的血液流变学的研究结果，为比较生理学研究提供基础资料．