固氮酶铁钼辅基的激光喇曼光谱和电子光谱特性

??色固氮?(A.vinclandii-230)相???分离的???基(FeMo-co),以NMF为溶剂,经Sephadex LII-20凝???析,或在20 000xg下离心30 min的上清液,不含任何的氨基?,研究了FeMo-co的?光?曼光谱和电子光谱,对FeMo-co中含有与S配基耦合的S-S配基的可能性进行了讨论。     

化学模拟生物固氮——Ⅶ.乙炔选择性还原成乙烯作为原子簇活性中心多核络合活化底物的一种判据

系统地比较了FeMo-co和固氮酶的各种模拟体系在KBH_4还原乙炔为乙烯的反应中的催化活性和选择性。FeMo-co(活性:转变数为34;选择性:99％C_2H_4)和本实验室合成的模型化合物(活性:转变数为20～30;选择性;91～95％)比其它固氮酶的模拟体系(MoO_4~(2-)-CySH;MoO_4~(2-)—CySH—Fe~(2 );MoOS_4~(2-)—胰岛素;[Fe_4S_4(SCH_2Φ)_4]~(2-);和MoS_4~(2-))具有较高的活性和选择性;这可作为FeMo—co及其合成模拟物的原子簇活性中心多核络合活化底物分子的一种判据.     

花生根瘤菌在自生条件下固氮和吸氢相关性

花生根瘤菌x_(-1)菌株在自生条件下和合适的培养基中,可诱导固氮酶及氢酶的活性,固氮酶反应产生的H_2(内源H_2)能直接诱导氢酶,氢酶活性表达的时间进程是在固氮反应之后,在外源H_2的存在下,固氮酶和氢酶则可同时表达,不同有机碳化合物对固氮酶与氢酶的影响不同,丙酮酸明显提高固氮活性,但对氨酶没有促进作用,蔗糖对固氮活性没有促进作用但对吸氢表现促进作用,分子H_2明显提高固氮活性,2.4-二硝基苯酚抑制需H_2的固氮活性,在外源H_2存在下其抑制作用更明显,铵抑制固氮酶的形成、固氮酶受铵抑制时氢酶也相应受到抑制。     

固氮酶钼铁蛋白活性辅基模拟物与缺辅基钼铁蛋白组合

随着固氮酶钼铁蛋白及其活性辅基(FeMo-CO)的研究逐渐深入,活性辅基结构的设计及模拟物的合成研究引起了国内外化学家的重视。活性辅基模拟物与缺辅基钼铁蛋白的生物组合规律研究对模拟物的定向合成、酶的半合成及固氮酶的催化机理等研究都有着重要意义。这方面研究已有一些报导,但系统研究不多。     

固氮酶铁钼辅因子模型化合物合成的研究——Ⅰ、光谱法研究合成方法的设计方案

本文讨论了以K_2MoS_4,FeCl_2,KOR(R=-CH_2CH_2OH或-CH_3)为基本原料,合成固氮酶铁钼辅因子(FeMo-co)模型物合成方案的设计依据。系统地考察这种体系的电子吸收光谱和激光拉曼光谱特征及其随时间的变化。实验结果支持了所提出合成方案的设计依据。     

固氮酶催化机制及化学模拟生物固氮研究进展

综述了固氖酶催化机制及化学模拟生物固氮研究的最新进展和问题．根据 固氮酶在生理条件下,具有固氮和放氢双重功能的事实,认为在研究确定N₂络合和 还原位点的同时,也应确定H⁺还原成H₂的位点,才能为化学模拟生物固氮提供全 面信息,以指导化学模拟物的设计与合成;并提出组成固氮酶活性中心原子簇的 [Fes₃Fe₃]和[MoS₃Fe₃]可能分别是N2还原和H⁺还原位点的设想．此设想如经验证, 将会简化模拟物的化学合成,可望加速实现在较温和的条件下(<300c,<5066kPa (50 atm))将N₂还原成NH₃。     

固氮酶固氮活性中心模型物的探索合成

关于固氮酶固氮活性中心的结构问题,我国化学家先后提出过具有独特见解的“福州模型”(M Fe_8S_7)和由“厦门模型”修订而成的“综合模型”(M_oFe_6S_6L_2)。“福州模型”和“综合模型”有某些共同的观点,即认为:固氮酶在固氮反应时必须具有鸟窝开口式网兜状基本结构单元作为活性中心,而且具有M Fe_6S_6孪合重烷体的基本骨架。这种学术见解亟待化学合成予以验证。遗憾的是,这类钼铁混合簇孪合型重     

从作物根际分离的多粘芽孢杆菌固氮作用的研究

用乙炔还原法，研究了从作物根际分离的５１株多粘芽孢杆菌的固氮作用，结果表明，２８株在有氧条件下培养能合成固氮酶并固氮，其中ＨＷ－１菌株固氮酶活性达７８．３×１０＾－６ｍｏｌ·ｈ＾－１，该菌株固氮活性在对数生长后期最高，最适固氮培养条件是３５℃和ｐＨ８．０，该菌株在有５％氧气的条件下培养时，固氮活性最高，在初始培养和乙炔还原体系中分别注入５０％氧气仍能检测到乙炔还原活性。培养基中ＮＨ４＾＋阻遏该菌株     

沼泽红假单胞菌固氮酶活性的调节

本文研究了沼泽红假单胞菌谷氨酰胺合成（简称ＧＳ）对其固氮酶活性的调节。外源氨的加入迅速抑制固氮酶活性，同时ＧＳ被高度腺苷酰化，随着氨的消耗，固氮酶活性逐渐恢复，ＧＳ腺苷酰化程度也逐渐降低。ＧＳ专一的不可逆抑制剂甲硫氨酸亚砜亚胺（简称ＭＳＸ）可以解除氨和谷氨酰胺对固氮酶的抑制作用。     

固氨酶活性中心模型的演进和酶催化机理

本文提出固氮酶活性中心的骈联双座双立方烷原子簇结构的活性中心模型,[S~*Fe_3S_2~*(L)]Mo[(L’)S_2~*Fe_3S~*],其中L和L’代表两个可以移开的配位体,如N_2,-H,或-NH_3。这个模型是前阶段先后提出的骈联双座单立方烷原子簇结构模型,Fe_2S_2~*·Mo_2O_2,和骈联双座三立方烷原子簇结构模型,Fe_2S_c~*(L)(L’)Mo_2[S_3~*Fe_3S~*]_2,的又一次演进。这三个模型所共有的骈联双座原子簇结构特征和三核络合固氮方式,主要都是以固氮酶己知反应的十来种底物和抑制剂CO作为化学探针并应用络合催化原理而推断出来的。至于钼离子的价态和周围微环境,以及三核究竟是两钼一铁还是一钼两铁,则是参考最近国际上关于固氮酶的科学实验新成就而作出相应的修正和演进的。骈联双座双立方烷原子簇结构(含单钼)比较符合Orme-Johson和Munck等的顺磁共振和穆斯鲍尔谱实验结果,能说明比较多的实验事实。本文还扼要地讨论了固氮酶反应中ATP驱动的电子和质子传递机理。     

提高钼泥中钼浸出率的实验研究

钼泥是冶炼钼铁飞扬的烟尘经水淋洗沉淀物 ,除含有一定量的钼外 ,还含有大量的石英石、硅酸盐、铁、铜、钙、镁、铝、铅等。从钼泥中提取钼 ,就是废物利用 ,化废为宝。但是 ,由于这个工艺过程复杂 ,达到很高的提取率很难 ,因此迄今为止 ,国际国内没有这种实验成功的先例。经过反复实验 ,用先酸后碱浸法 ,由钼泥中提取钼的提取率达到 99%以上 ,该项实验的成功 ,每年可节约5 0 0多万元资金 ,同时还减少了环境污染 ,具有很大的经济效益和社会效益     

微型化学实验在合成研究中的应用实例

通过微型实验在新法合成高柠蒙酸内酯和在水热合成中的应用实例 ,说明微型实验在化学科研中同常规方法一样有其不可替代的作用 ,是化学科研方法的重要发展和补充     

Present status and development on biological nitrogen fixation research in China

This presentation introduces the advances in biological nitrogen fixation research abroad, in particular,describes the great progress and achievements on its research in China as follows: collection of rhizobial resources and establishment of the largest database of Rhizobium in China, correction and development of Rhizobium taxonomy in international; discovery of a couple of nif genes, identification and unification of linkage among the nif gene operons of Klebsiella pneumoniae, finding of regulative mechanism of positive regulation nif gene and its sensitivity to oxygen,temperature; finding of the activity of nodulation gene nodD3 product in Sinorhizobium meliloti which is not controlled by flavonoid produced from its host alfalfa; finding of the association between expression of genes coding the products for carbon utilization and nitrogen metabolism and their regulations; chemical synthesis of nodulation factor of Sinorhizobium meliloti; constructions of engineered nitrogen fixers and utilization in practice based on the research of gene expression and regulation; chemical simulation of the structure and function of nitrogenase and bringing forward the model of nitrogenase active center for the first time in international and synthesis of model compounds which were paid attention by colleagues abroad. Finally, the development of nitrogen fixation research in China in future has been put forward, suggesting that the nif gene regulation and its role in providing crops with nitrogen element, signal transduction and molecular interactions between Rhizobium and legume, coupling between carbon and nitrogen metabolisms, nitrogen fixation and photosynthesis, and functional genomics of nitrogen-fixing nodule symbiosis, etc., would be actively worked on.     

自保护药芯焊丝焊缝金属化学成分与性能的研究

自保护药芯焊丝焊缝金属中氧、氮含量较高，而塑性、韧性较低。根据自保护焊接化学原理，分析了铝、钛等金属对脱氧和固氮的作用，研究 了适合自保护焊接合理的焊缝金属化学成分。     

共生固氮体系大豆种子氨基酸组分分析

对三对共生固氮体系大豆种子氨基酸组分的分析表明，大豆种子氨基酸组分没有因大豆作物产量的提高而下降，通过施用相应的根瘤菌促其形成或加强共生固氮体系从而提高大豆作物产量，这种增产从氨基酸水平分析是有效的。     

Hydrogenation and cleavage of dinitrogen to ammonia with a zirconium complex

Molecular nitrogen is relatively inert owing to the strength of its triple bond, nonpolarity and high ionization potential. As a result, the fixation of atmospheric nitrogen to ammonia under mild conditions has remained a challenge to chemists for more than a century. Although the Haber-Bosch process produces over 100 million tons of ammonia annually for the chemical industry and agriculture, it requires high temperature and pressure, in addition to a catalyst, to induce the combination of hydrogen (H2) and nitrogen (N2). Coordination of molecular nitrogen to transition metal complexes can activate and even rupture the strong N-N bond under mild conditions, with protonation yielding ammonia in stoichiometric and even catalytic yields. But the assembly of N-H bonds directly from H2 and N2 remains challenging: adding H2 to a metal-N2 complex results in the formation of N2 and metal-hydrogen bonds or, in the case of one zirconium complex, in formation of one N-H bond and a bridging hydride. Here we extend our work on zirconium complexes containing cyclopentadienyl ligands and show that adjustment of the ligands allows direct observation of N-H bond formation from N2 and H2. Subsequent warming of the complex cleaves the N-N bond at 45 degrees C, and continued hydrogenation at 85 degrees C results in complete fixation to ammonia.     

Specific degradation of photosystem II D1 protein by a protease （Air3815） in heterocysts of the cyanobacterium Anabaena sp. PCC7120

Some filamentous cyanobacteria form heterocysts under conditions lacking combined nitrogen for nitrogen fixation.Photosystem II is removed from heterocyst during the process of cell differentiation.Here,we demonstrate that Alr3815 is a protease that is capable of degrading D1 protein of photosystem II.Strain-322,which lacks alr3815,is impaired in nitrogen fixation in air because some oxygen evolving activity is retained in its heterocysts.Our results also suggest that calcium may play a regulatory role in D1 degradation during heterocyst differentiation.     

高柠檬酸盐对固氮酶铁钼辅基重组活性的影响

用高柠檬酸铁、柠檬酸钠、ＡＴＰ和Ｎａ２ＭｏＯ４分别处理ＦｅＭｏｃｏ，然后与ＵＷ４５组份Ⅰ蛋白进行重组，结果发现，高柠檬铁和柠檬酸钠分别使ＦｅＭｏｃｏ重组体的Ｃ２Ｈ２还原活性提高６７％和５４％，Ｎ２还原活性分别提高１７０％和１３５％．ＦｅＭｏｃｏ与ＡＴＰ预作用后再分别与高柠檬酸铁、柠檬酸钠作用，其重组体的Ｃ２Ｈ２还原活性分别提高１２１％和１１９％，而Ｎ２还原活性分别提高３０３％和１３５％．而ＦｅＭｏｃｏ，ＦｅＭｏｃｏ－高柠檬酸铁体系及ＦｅＭｏｃｏ－ＡＴＰ－高柠檬酸铁体系与Ｎａ２ＭｏＯ４作用后，重组体的Ｃ２Ｈ２还原活性分别下降５％，１２％及２１％．ＦｅＭｏｃｏ－高柠檬酸铁体系在１４．６Ｋ下的ＥＰＲ谱，与单独ＦｅＭｏｃｏ的略有不同，而ＦｅＭｏｃｏ－ＡＴＰ－高柠檬酸铁体系的ＥＰＲ谱则与前者有明显的差异．研究结果表明，高柠檬酸可能是ＦｅＭｏｃｏ的有机组份，它可能结合在ＦｅＭｏｃｏ的Ｍｏ原子上，而这种结合是比较松散的．     

Spatial coupling of nitrogen inputs and losses in the ocean

Nitrogen fixation is crucial for maintaining biological productivity in the oceans, because it replaces the biologically available nitrogen that is lost through denitrification. But, owing to its temporal and spatial variability, the global distribution of marine nitrogen fixation is difficult to determine from direct shipboard measurements. This uncertainty limits our understanding of the factors that influence nitrogen fixation, which may include iron, nitrogen-to-phosphorus ratios, and physical conditions such as temperature. Here we determine nitrogen fixation rates in the world's oceans through their impact on nitrate and phosphate concentrations in surface waters, using an ocean circulation model. Our results indicate that nitrogen fixation rates are highest in the Pacific Ocean, where water column denitrification rates are high but the rate of atmospheric iron deposition is low. We conclude that oceanic nitrogen fixation is closely tied to the generation of nitrogen-deficient waters in denitrification zones, supporting the view that nitrogen fixation stabilizes the oceanic inventory of fixed nitrogen over time.