Complete assignment of 1H, 13C and 15N chemical shifts for bovine β-lactoglobulin: Secondary structure and topology of the native state is retained in a partially unfolded form

Although -lactoglobulin (-LG) has been studied extensively for more than 50 years, its physical properties in solution are not yet understood fully in terms of its three-dimensional (3D) structure. For example, despite a recent high-resolution crystal structure, it is still not clear why the two common variants of bovine -LG which differ by just two residues have different aggregation properties during milk processing. We have conducted solution-state NMR studies on a recombinant form of the A variant of -LG at low pH conditions where the protein is partially unfolded and exists as a monomer rather than a dimer. Using a¹³ C,¹⁵N-labelled sample, expressed in Pichia pastoris, we have employed the standard combination of 3D heteronuclear NMR techniques to obtain near complete assignments of proton, carbon and nitrogen resonances. Using a novel pulse sequence we were able to obtain additional assignments, in particular those of methyl groups in residues preceding proline within the sequence. From chemical shifts and on the basis of inter-residue NOEs, we have inferred the secondary structure and topology of monomeric -LG A. It includes eight antiparallel -strands arranged in a barrel, flanked by an -helix, which is typical of a member of the lipocalin family. A detailed comparison with the crystal structure of the dimeric form (for a mixture of A and B variants) at pH 6.5 reveals a close resemblance in both secondary structure and overall topology. Both forms have a ninth -strand which, at the higher pH, forms part of the dimer interface. These studies represent the first full NMR assignment of -LG and will form the basis for a complete characterisation of the solution structure and dynamics of this protein and its variants.     

红外光谱技术在生物过程监测中的应用

在线监测化学组分的浓度对许多生物过程都是十分必要的。然而,探头需耐高温灭菌的要求和生物体系自身的复杂性给许多分析技术的在线监测带来了困难。近几年,随仪器和数据处理技术的迅速发展,应用红外光谱技术对生物过程的原位或在线监测日益广泛。本文对红外过程分析技术进行了较全面的综述,介绍了红外分析的原理、进展及在生物过程监测中的应用。     

对-氯代苯胺(PCA)在填充床生物反应器中的降解作用

以氯代苯胺(PCA)为选择基质,用驯化技术从降解对二氯苯(p-DCB)的富集培养物中得到了以同化PCA为唯一碳源和氮源的混合微生物。将这种固定在填充床反应器中的微生物用于PCA的降解作用研究中。在该反应器里,PCA的生物降解遵循Logistic方程q=q_max/(1+e^α-βU_v).由方程求出了主要的动力学常数,K_s(半速率常数)和q_max(最大比基质降解速率).于PCA降解的同时,释放氯离子到培养基中。在水力停留时间3h, 进水PCA浓度为360mg·L^-1情况下,基质的体积降解率达到125mg·L^-1·h^-1;基质的百分去除率为91%.     

森林植被的自然火干扰

森林植被的自然火干扰邱扬（山西大学黄土高原研究所,太原０３０００６）ＮａｔｕｒａｌＦｉｒｅＤｉｓｔｕｒｂａｎｃｅｏｆＦｏｒｅｓｔＶｅｇｅｔａｔｉｏｎ．ＱｉｕＹａｎｇ（ＩｎｓｔｉｔｕｔｅｏｆＬｏｅｓＰｌａｔｅａｕ,ＳｈａｎｘｉＵｎｉｖｅｒｓｉｔｙ,...     

内蒙古中南部轮藻植物区系及分布特点

内蒙古中南部轮藻植物以温带成分占绝对优势,有较多的中国特有植物;种类以轮藻属为主,其中丛刺轮藻、灰色轮藻为本地的广布和优势种;分布以上河套平原的种类、数量最多;另外,轮藻植物的形态结构、种类组成及分布均与其生长的环境紧密相关。     

用Bac-to-Bac杆状病毒表达系统高效表达绿色荧光蛋白标记的HBVe抗原

通过基因工程操作,使乙型肝炎病毒ｅ抗原（ＨＢｅＡｇ）基因与绿色荧光蛋白基因（ＧＦＰ）融合,用新型Ｂａｃ－ｔｏ－Ｂａｃ杆状病毒表达系统在昆虫细胞中高效表达了ＨＢｅＡｇ－ＧＦＰ双功能融合蛋白。经ＥＬＩＳＡ法和荧光显微镜观察证实,表达产物既能发射易于检测的绿色荧光,又具有ＨＢＶ的ｅ抗原活性,为免疫诊断新方法的建立进行了有益的探索     

血水草地下部分白屈菜红碱的含量测定

提出一个单波长扫描测定血水草地下部分白屈菜红碱含量的方法,药材以95％的乙醇提取在320nm处测定,回收率为96.3％(CV=2.39％),结果稳定可靠。     

白鲜皮中白鲜碱含量测定

白鲜皮中白鲜碱含量测定朱丹妮徐强邱南生（中国药科大学,南京２１００３８）ＴｈｅｑｕａｎｔｉｔａｔｉｖｅｄｅｔｅｒｍｉｎａｔｉｏｎｏｆｄｉｃｔａｍｉｎｅｉｎｒｏｏｔｂａｒｋｏｆＤｉｃｔａｍｎｕｓｄａｓｙｃａｒｐｕｓＴｕｒｃｚ．ＺｈｕＤａｎＮｉ,Ｘｕ...     

龙胆VA菌根真菌的分离和鉴定

采用湿筛法和单孢接种技术,从东北龙胆根际土壤中分离到能在东北龙胆组培苗上形成VA菌根的真菌孢子和孢子果呆,依其显微形态特征对部分菌株进行鉴定,大多属于球囊霉属（Glomus）中的漏斗孢球囊霉（Glomusmosseae）和地球囊霉（G．geosporum）     

红三叶人工草地营养元素的生物循环

 本文研究了我国北亚热带高海拔地区红三叶人工草地11种营养元素的生物循环特征。结果表明:1.营养元素的存留量、归还量和吸收量均可分为5个水平;(1)高量级：氮、钾、钙;(2)中量级：磷、镁;(3)低量级：铁;(4)少量级：锰、锌、铜、硼;(5)微量级：钼。2．红三叶群落地上部的净生产量、自然归还量和元素的存留量均显著高于地下部。3．红三叶人工草地的元素输出量以氮、钾、钙较大。此外,对草用和种用红三叶群落营养元素生物循环特征的差异进行了比较。为维持本区红三叶人工草地营养元素的平衡,目前必须施用磷肥,施用量不能小于250kg·hm-2过磷酸钙。