天花粉蛋白二级结构的圆二色性研究

本文报告了室温条件下在185—330nm波长范围内天花粉蛋白的CD谱测定的结果。利用205—240nm区间的CD谱,借助参考CD谱用最小二乘拟合的方法,计算得天花粉蛋白中α螺旋平均含量为24％,β折叠含量为30％,无序构象含量为46％。     

天花粉蛋白的化学 Ⅵ.用激光拉曼光谱研究天花粉蛋白的二级结构

由天花粉蛋白的水和重水溶液的激光拉曼光谱,测得酰胺Ⅲ谱带1240cm~(-1)和酰胺I谱带1632,1660cm~(-1)对CH_2弯曲模式1448cm~(-1)的强度比值。按Lippert等建立的方程组作定量计算,求得天花粉蛋白的二级结构含量为α-螺旋43.5％,β-折叠31.3％和无序25.2％,它们与4 分辨率天花粉蛋白单晶X射线衍射法的结果相一致。同时,研究了上述溶液的冻干粉状固体的二级结构,经过冻干,使其中约10％的β-折叠转变成无序构象,而α-螺旋含量无明显变化。在水溶液中,由测得的I_(850)/I_(830)比值计算,天花粉蛋白中的酪氨酸残基约有80％呈“暴露式”。     

天花粉蛋白的化学VI.用液光拉曼光谱研究天花粉蛋白的二级结构

由天花粉蛋白的水和重水溶液的激光拉曼光谱,测得酰胺III谱带1240cm[-1]和酰胺I谱带1632,1660cm[-1]对CH2弯曲模式1448cm[-1]的强度比值,按Lippert等建立的方程组作定量计算,求得天花粉蛋白的二级结构含量为α-螺旋43.5%,β-折叠31.3%和无序25.2%,它们与4A分辨率天花粉蛋白单晶X射线衍射法的结果相一致,同时,研究了上述溶液的冻干粉状固体的二级结构,经过冻干,使其中约10%的β-折叠转变成无序构象,而α-螺旋含量无明显变化,在水溶液中,由测得的I850/I830比值计算,天花粉蛋白中的酪氨酸残基约有805呈"暴露式"。     

天花粉蛋白化学 Ⅳ.天花粉蛋白的基本一级结构

前文报道从我国民间用于引产的中草药天花粉中提取到活性组分结晶天花粉蛋白和它的物理化学性质,N-端氨基酸顺序的测定及其溴化氰降解碎片CBa的顺序分析. 天花粉蛋白是一个由224个氨基酸残基组成的单一肽链的简单蛋白质,其N-末端残基为Asp,C-端顺序经羧肽酶A测定,并结合其水解动力学的计算机拟合为     

天花粉蛋白分子的三维结构

本文报道了我们最近建立的单斜晶胞内一个不对称单元中两个天花粉蛋白分子的模型,指出蛋白分子结构可以划分为大小两个结构域以及二级结构的一些特点,描述了独立单元中以一种非对称方式相关联的两个蛋白分子的差异及其相互作用,并解释了重原子衍生物的结合位置。     

天花粉蛋白一级结构的修正及不同产地天花粉蛋白的研究

胰蛋白酶酶解天花粉蛋白, 用高效液相色谱分离酶解肽段, 用顺序仪测定其有关肽段的顺序。用羧肽酶A, B, Y测定了天花粉蛋白C-端和天花粉蛋白溴化氰降解肽CB1的C-端顺序, 修正了我们1985年测定的天花粉蛋白一级结构, 证明天花粉蛋白由246(7)氨基酸残基所组成, 除C-端微观不均一外, 与Collins结果一致。同时比较了芜湖产天花粉蛋白一级结构与平湖产的天花粉蛋白一级结构, 没有发现两者的一级结构有差别。     

用MALDI-TOF-MS法快速测定天花粉蛋白分子量

采用ＭＡＬＤＩ－ＴＯＦ－ＭＳ法快速测定了天花粉蛋白的分子量,并讨论和对比了三种不同基质对其影响,认为用基质芥子酸是最佳适宜条件。实验结果表明本方法优于其它传统的测定生物大分子分子量方法。     

天花粉蛋白1.73分辨率结构测定及其精化

本文报道了用面探测器收集一套1.73分辨率天花粉蛋白(TCS)正交晶体的X射线衍射数据,利用已知的α苦瓜子蛋白模型,取10—4范围的TCS强度数据,应用分子置换法测定了晶体结构,并且采用限制参数最小二乘法在10—1.73分辨率范围内修正模型结构。修正结果,晶体学R因子为0.186,键长标准偏差为0.013,键角标准偏差为2.48°,一个不对称单位中找到133个水分子。本文详细描述了天花粉蛋白分子的结构、温度因子、氢键、结合水、保守残基的分布以及分子间相互作用。保守残基14Tyr的羟基与157位的羰基氧形成的氢键,对维持活性部位构象有重要作用;保守残基160Glu和它在活性部位的构象对酶的催化活性起着关键性作用。     

1.73分辨率天花粉蛋白晶体中的水结构

本文报道的天花粉蛋白晶体中水的结构模型,包括了133个水分子,其中118个同蛋白的原子成氢键。天花粉蛋白内部有4个分立的水分子,其中2个水分子W251和W252分剔与A5螺旋变形部位的残基156Gln和157Ser的侧链成氢键,对维持活性部位的构象有贡献。晶体中水结构的比较结果表明,核糖体接近蛋白时,会诱导蛋白活性部位残基的构象发生变化,使各催化基团按催化效果最佳的构象排布,并激活一个水分子(W257)直接参与核糖体失活作用。     

Analysis of Block and Statistical Copolymers by Gel Permeation Chromatography: Estimation of Mark-Houwink Constants

Abstract

A method is introduced for the estimation of Mark-Houwink constants of block and statistical copolymers. The homopolymer Mark-Houwink constants and copolymer composition are required. Use of estimated Mark-Houwink constants in GPC analyses gives results which agree well with those calculated with experimentally determined constants. Comparisons between this method and those of Runyon and coworkers (11) and Chang (12) are made for block copolymers. Chang's method was also extended to statistical copolymers, and where it compared closely with the one introduced here. The use of copolymer Mark-Houwink constants as a qualitative measure of polymer compatibilities in different solvents is also discussed.     

Conformational Flexibility of the Acetoxyphenyl Group Studied by Statistical Analysis of Crystal Structure Data

The preferred conformation of the acetoxyphenyl fragment shows a planar acctoxy (AcO) group perpendicular to the Ph ring. Steric hindrance strongly limits and affects rotation about the C? OCOCH₃ bond: if the A_cO group twists away from its perpendicular conformation, the carbonyl oxygen moves to keep the nonbonded distance to the atoms in ortho-position maximal. This is achieved by some twisting about the O? COCH₃ bond correlated with angle bending at the ipso-C-atom and ester O-atom. The maximum observed deviation away from the perpendicular conformation is ～ 47°. In the case of one or two ortho-hydrogens, deviations of the AcO group from the perpendicular conformation tend to be larger than in the case of two substituents.     

Conformational Flexibility of the Methoxyphenyl Group Studied by Statistical Analysis of Crystal Structure Data

In a large sample of observed methoxyphenyl groups, the twist angle τ about the MeO-C_Ph bond measuring internal rotation of the MeO group shows a continuous distribution with maxima at (0°) (coplanar conformation) and (～90°) (perpendicular conformation). The preferred conformation of methoxyphenyl depends on the nature of the ortho--substituents: In general, it is coplanar in the case of one or two ortho-hydrogens, and perpendicular in the case of two substituents. The internal rotation of the MeO group is accompained by systematic variations in bond angles and bond distances: 1 if MeO is twisted out of plane, the bond angle CH₃? O? C_Ph decreases from 117.7°, until it reaches a minimum of 114.9° at τ = ±90°. The O? C? C angle which is syn to CH₃ for τ = 0° decreases from 124.6° to a minimum of 115.4° at τ = ±180°. These angles changes keep the nonbonded distance CH₃ …? ortho substituent maximal during internal rotation of MeO and tend to minimize the corresponding strain energy. (2) In the perpendicular conformation, the O-atom is ～ 0. 06 Å displaced from the Ph plane, O and CH₃ and being on opposite sides of this plane. In addition, small but systematic increases of bond lengths MeO? C_Ph and CH₃? O are observed. These variations indicate a decrease in conjugation with increasing twist angle. Their interdependence during twisting and the magnitudes of the changes are close values obtained by ab initio calculations.     

正交晶系天花粉蛋白2.4分辨率的晶体结构和分子结构

在酸性条件下(pH=5.4)培养出正交晶系天花粉蛋白晶体。用面探测器收集了X射线衍射强度数据。以C2空间群天花粉蛋白2.6分辨率的晶体结构中的分子模型作为已知结构模型,用分子置换法解出正交晶系P2_12_12_1空间群天花粉蛋白的晶体结构。所得到的初始结构模型先后用模拟退火法和立体化学制约的最小二乘修正技术对原子坐标及温度因子进行修正。最后在2.4分辨率范围内模型的β因子为0.197,键长的均方根误差为0.021,键角距离的均方根误差为0.081。分子结构模型与(2Fo—Fc)为系数的电子云密度图吻合得很好。键长键角合理。结构测定结果表明,P2_12_12_1;空间群天花粉蛋白的分子的空间结构与单斜晶系C2空间群中的分子结构甚为相似。     

中等化学教育类专业期刊的文献统计分析

目前,我国有关中等化学教育的专业期刊主要有:①<化学教育>、②<化学教学>、③<中学化学教学参考>、④<中学化学>、⑤<中学化学教与学>、⑥<化学教与学>.期刊①②③④属原创性质;期刊⑤属复印资料性质;近年来期刊⑤没有转载或索引期刊⑥的文章.     

Molecular Replacement Studies of Cucurmosin from Cucurbita Moschata:Structure Homology with Trichosanthin

1 INTRODUCTION Many plants contain proteins that are capable of inactivating ribosomes and therefore are called ribosome-inactivating proteins or RIPs[1]. RIPs are RNA N-glycosidases that inactivate ribosomes through a site-specific deadenylation of the large ribosomal RNA[2, 3]. RIPs are also capable of inactivating many nonribosomal nucleic acid substrates and can be considered as polynucleotide: adenosine glycosidases[4～6]. There are two types of RIPs: type I, single chain pr…