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91.
A procedure is described, based on a spline-function representation of ab initio peptide conformational geometry maps, that allows one to predict backbone bond distances and angles of proteins as functions of the peptide ?(N-Cα)/Ψ(Cα-C′) torsions with an accuracy comparable to that of high-resolution protein crystallography. For example, for the more than 40 residues of crambin, the rms deviation between predicted and crystallographic values of N-Cα-C′ is 1.9° for the 1.5 Å resolution structure and 1.9° for the 0.83 Å resolution structure, compared with angle variations of < 10°. Accurate information on protein backbone geometries is important for establishing dictionaries of flexible geometry functions for use in empirical peptide and protein modeling. © 1995 John Wiley & Sons, Inc. 相似文献
92.
Choline kinase of rat brain was purified approximately 200,000 fold using acid precipitation, ammonium sulphate fractionation, Q-Sepharose, Octyl-Sepharose and AH-Sepharose chromatography. The ability of this enzyme to catalyze the phosphorylation of choline, ethanolamine (Etn), monomethylethanolamine (MeEtn), dimethylethanolamine (Me2Etn) and sphingosine was investigated. Choline kinase was separated from sphingosine kinase. The fraction with highly purified choline kinase had four major polypeptides with different molecular masses and possessed activities towards choline, Etn, MeEtn and Me2Etn. Two forms of choline kinase were obtained when the enzymatically active fractions eluted from the Q-Sepharose column were subjected to a horizontal isoelectrofocusing electrophoresis. One form focused around pH 4.7 and is able to phosphorylate choline, Etn, MeEtn and Me2Etn. The other form focused around pH 10 and possessed only choline kinase activity. The latter form of choline kinase did not display classical Michaelis-Menten's mechanism but revealed a positive co-operative pattern for two choline binding sites. This form was purified to apparent homogeneity with a approximate molecular mass of 14.4 kDa.Abbreviations Etn
ethanolamine
- MeEtn
N-monomethylethanolamine
- Me2Etn
N, N-dimethylethanolamine 相似文献
93.
Improved resolution with one-dimensional polyacrylamide gel electrophoresis: myofibrillar proteins from typed single fibers of human muscle 总被引:1,自引:0,他引:1
Standard procedures for one-dimensional discontinuous sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and silver staining were modified to give more effective separation and an improved resolution of human skeletal muscle proteins. In this system, an electrophoresis buffer composed of 100 mM L-isoleucine, 25 mM Tris base, and 0.1% SDS was used. The separating gel consisted of 16% acrylamide with N,N'-methylenebisacrylamide as a crosslinker (1:23), 0.4% SDS, 1.5 M Tris-HCl, pH 8.8. By the present procedure, the slow and the fast forms of myosin light chains (LCs, LCf) and other contractile proteins from human muscle could be better separated. The silver stain is based on a combination of methods previously described. The modified method requires a small fragment of a single fiber to observe as few as 10 ng of myofibrillar muscle proteins. The described simplifications made it possible to assay and compare up to 40 single fibers in the same electrophoretic run. Improved separation of other proteins migrating at basic pH could be achieved by a similar approach. 相似文献
94.
水生植物叶片的功能性状特征与陆生植物有所不同,同时叶脉类型也显著影响叶片的功能性状。本研究选取9种具有不同叶脉类型的水生植物,通过对叶脉进行直接损伤,分析叶片性状(形态、色素含量和叶绿素荧光指标)在叶脉受损后的变化程度与叶脉类型的关系。结果显示:具有平行脉的3种水生植物对叶脉损伤具有较强的耐受性;具羽状脉的4种植物主脉受损后显著抑制叶片生长,而侧脉受损的影响在不同物种间有所不同,具有物种特异性。本研究可为大型湖泊水生植物修复的水生物种筛选提供参考。 相似文献
95.
塔里木沙拐枣(Calligonum roborowskii A.Los.)是仅分布于我国西北地区荒漠环境的特有种,其果实为不开裂而周围有椭圆形刺毛的瘦果,以果实为单元进行扩散和萌发。本文采用野外观察与室内控制实验相结合的方法,对塔里木沙拐枣刺毛在果实扩散、吸水、脱水及萌发中的作用进行研究。结果显示:不同贮藏时间的果实颜色、大小、重量及刺毛长度存在显著差异。完整果实在水面漂浮时间及水媒扩散能力比去除刺毛的果实更强。完整果实在1 m/s和4 m/s风速下的扩散距离比无刺毛果实的扩散距离长。10 mmol/L赤霉素(AG3)及不同干藏时间处理的完整果实与无刺毛果实在20℃/30℃光照和黑暗条件下的萌发率间存在显著差异,其中无刺毛果实的萌发率要高于完整果实的萌发率。室外盆栽实验显示,无刺毛果实的萌发率比完整果实高,说明果实刺毛对果实萌发有抑制作用。研究结果表明果实刺毛对塔里木沙拐枣在塔克拉玛干沙漠边缘荒漠环境中的扩散、萌发及种群更新具有重要的辅助作用。 相似文献
96.
Ultraviolet light induced preferential cross-linking of histone H3 to deoxyribonucleic acid in chromatin and nuclei of chicken erythrocytes 总被引:3,自引:0,他引:3
Histones have been cross-linked to DNA in chicken erythrocyte nuclei and chromatin by using ultraviolet light irradiation at 254 nm. Following irradiation, cross-linked histone-DNA adducts were isolated and purified by hydroxylapatite chromatography, and the DNA component was subjected to acid hydrolysis. Of several hydrolysis techniques investigated, trichloroacetic hydrolysis of the DNA component of the adducts was found to be most effective. Histones isolated from hydrolyzed histone-DNA adducts were characterized by gel electrophoresis and fingerprint analysis. No histone-histone protein adducts were observed. All histone fractions have been shown to cross-link DNA in nuclei or chromatin by utilizing the technique employed, but with different propensities. The order of observed cross-linking, deduced from kinetic experiments, is H1 + H5, H3 greater than H4 greater than H2A much greater than H2B. The preferential binding of the core histone H3, as compared to the other core histones, is discussed in light of recent data concerning histone-DNA interactions and nucleosome structure. The use of the ultraviolet light technique as a conformational probe to study chromatin is also discussed. 相似文献
97.
98.
99.
急性病毒性肝炎的发病率慢性肝炎患病率和肝病死亡率的研究 总被引:15,自引:0,他引:15
1984~1987年,在黑龙江、河北、河南、湖南、上海五个省市城乡10.08855人口中进行急性肝炎发病率、慢性肝炎患病率、与病毒性肝炎有关的肝病死亡率的研究。急性肝炎标化发病率为152.19/10万,主要发生在20~50岁组人群;因无甲肝暴发流行,除上海外各点季节发病率分布均衡。慢性肝炎标化患病率为158.25/10万(诊断标准为6个月前有明确急性肝炎病史,现有明显的临床症状或体征,肝功能异常,故实际慢肝患病率要高于此数字);与病毒性肝炎有关的肝病死亡(包括肝癌)标化率为22.65/10万,其中肝病为 13.14/10万。男性死亡率显著高于女性。 相似文献
100.
为了解四川省自贡地区3~5岁幼儿乙型肝炎病毒(HBV)感染情况,并探索与感染有关的因素,1985年调查了1167名幼儿,其HBV总感染率为41.13%,HBsAg阳性率12.68%。幼儿的HBV感染与母亲HBsAg阳性密切相关。共检查母亲409例,38例HBsAg阳性,其幼儿HBsAg阳性率为50%(19/38),HBsAg阴性的母亲371例,其幼儿HBsAg阳性率9.97%(37/371),来自HBsAg阳性母亲的阳性子女占33.3%(19/56)。1986年随访HBV易感幼儿448例,HBV年感染率为12.95%(58/448),HBsAg年阳转率3.79%。HBV年感染率与原幼儿班级HBsAg阳性率的高低有关。 相似文献