二甲胺基尾式卟啉铁与双原子小分子CO,NO配位性质的研究

本文报道了二甲胺基尾式卟啉铁{中位-[邻(4-二甲胺基丁酰胺基)苯基]三苯基卟啉合铁(II)}同双原子小分子CO, NO的配合物的UV, MCD, ESR光谱和电化学性质, 测定了它与CO轴向加合平衡常数为1.38x10^7M^-^1, 讨论了尾端配体对CO与中心离子铁的成键影响。NO配合物的ESR和循环伏安结果表明, NO的配位削弱了尾端N与中心离子铁的键强, 并用分子轨道理论解释了这一结果。     

小分子配位对血红素活性影响的原子-键电负性均衡方法研究

应用原子-键电负性均衡方法, 计算了血红素与小分子的配位络合物的电荷分布和Fukui函数. 血红素与氧、水、一氧化碳和一氧化氮结合时, 铁离子电荷转移到配体原子上. 活性中心铁离子的Fukui函数均大于氧和水配体中的配位氧原子, 而小于一氧化碳和一氧化氮配体中的配位碳和配位氮原子的Fukui函数. 从Fukui函数可以得出, 一氧化碳和一氧化氮很难从它们与活性中心血红素结合的配位络合物中解离出来, 而氧和水易于从它们与血红素结合的配位络合物中解离出来, 进而, 血红素可以再与其它配体结合. 血红素与KCN和NaN3抑制剂作用时, 铁离子的Fukui函数均小于与其配位的碳和氮原子, 表明在过氧化氢酶中血红素的活性作用减弱或被抑制.     

光谱法研究肌红蛋白与亚硝酸钠的相互作用

采用紫外-可见光谱、荧光光谱、同步荧光光谱和圆二色光谱法研究了肌红蛋白与亚硝酸钠配位反应的光谱学性质.结果表明,肌红蛋白与亚硝酸钠配位反应的进行与血红素中心铁原子的价态有关;当肌红蛋白活性中心Fe为三价时,亚硝酸钠主要与蛋白质上的氨基酸发生作用.而当肌红蛋白的活性中心Fe为二价时,亚硝酸钠则与卟啉铁配位,形成亚硝基亚铁肌红蛋白.荧光光谱表明亚硝酸钠的加入改变了肌红蛋白氨基酸残基的微环境,同步荧光光谱数据显示肌红蛋白与亚硝酸钠作用位点更接近于色氨酸残基,同时CD数据也表明肌红蛋白与亚硝酸钠作用后,其α-螺旋含量降低了19.33%,二级结构发生明显变化.     

可溶性鸟苷酸环化酶介导NO信号转导的结构基础及其分子机制研究

可溶性鸟苷酸环化酶(sGC)是NO信号转导通路中的核心金属酶,是NO的敏感器和受体.sGC含有?和?两个亚基,每个亚基分别具有3个结构域,包括血红素结构域、中心结构域和催化结构域,两个亚基的血红素结构域共享有一个血红素,NO结合到sGC的血红素后,激活sGC,催化其底物GTP转化为二级信号分子cGMP,开启PKG信号通路,导致血管舒张.NO信号转导通路异常将导致多种疾病的发生,如多种心血管疾病、肺动脉高血压、心力衰竭及神经退行性疾病等.近20年来,关于sGC的结构、功能、激活机制及其在生理与病理中的作用有了很多进展.本文重点对sGC的结构、功能及其活化/失活机制研究进展进行综述.     

尾式缬氨酸四苯基卟啉锌(Ⅱ)与咪唑轴配反应的光谱和热力学

用金属卟啉化合物来模拟血红素、细胞色素等天然卟啉化合物的生理过程一直是配位化学重要的研究课题。人们发现 ,血红蛋白中的血红素是通过铁与组氨酸残基的侧链咪唑配位于蛋白质上 ,因此 ,人们对金属卟啉与咪唑类配体的轴向配位反应研究产生了极大兴趣 [1] 。有关取代四苯基卟啉金属配合物的合成和轴配反应热力学研究已有很多报道 ,但人们的研究尚处在对称且苯环上连有较小取代基的四苯基卟啉锌、钴、铁等模拟化合物的合成、结构表征及光谱和配位反应热力学的研究阶段 [2 -4 ]。对于结构不对称且卟啉中苯环上连有氨基酸的四苯基卟啉配合物…     

一氧化氮的生物化学及其生理和药理效应

本文论述了一氧化氮（nitric oxide,NO）的生物化学特征及其生理效应和药理效应。NO是生物信使分子和效应分子,NO本身是一个气体分子。NO参与细胞内一系列的生物化学反应,而且,还广泛地影响机体内的生理病理过程。本文阐述了NO在体内的合成机理以及NO供体的基本药理作用,并指出NO生成过多,或者合成障碍,均对机体产生影响。NO相关的新型药物已研制成功,并在临床治疗上初步应用,NO成为生物医学领域研究的热点和前沿课题之一。机体内NO气体信使分子的发现,对于今后其他生物信使的发现提供了重要的启示。     

钴、钌在加氢脱硫催化剂中的助剂作用

以CO, NO, H_2, O_2作为探针分子, 应用红外光谱法和化学吸附法研究了还原态Co-Mo/Al_2O_3, Ru-Mo/Al_2O_3和Ru-Co-Mo/Al_2O_3催化剂中Co, Ru的助剂作用。结果表明, Co担载在Mo/Al_2O_3上, 由于Co与Al_2O_3之间的相互作用减弱, Co中心上吸附CO和NO的能力增强, 改变了Mo中心吸附CO, NO, H_2,O_2的能力, 表现出Co-Mo/Al_2O_3上的Co中心性质显著地不同于Co/Al_2O_3。Ru担载在Mo/Al_2O_3或Co-Mo/Al_2O_3催化剂上, Ru自身的吸附CO, H_2, O_2能力降低, 但促进了MoO_3的还原, 使CO, NO, H_2, O_2在Mo中心上的吸附量增加。可以认为, Ru的作用是活化, 解离氢, 通过溢流氢促进配位不饱和的Mo中心生成。Ru的这种作用比Co明显。     

功能化微纳米硅胶表面亚铁配位化学及其催化降解邻苯二酚的性质

含吡啶硫醚有机分子功能化的微/纳米硅胶粒子利用表面有机分子分别与氯化亚铁和硫酸亚铁发生配位作用,制得两种功能化材料,即FeC@L-NSiG和FeS@L-NSiG。采用红外光谱(FTIR)、紫外可见吸收光谱(UV-Vis)、热重(TGA)和扫描电镜(SEM)对这两种材料进行了表征;同时对材料表面Fe(Ⅱ)可能的配位化学性质以及其催化双氧水氧化降解邻苯二酚的性能进行了研究。为了探究两种材料表面上亚铁中心的配位化学性质,合成了类似于功能化微/纳米硅胶表面上的有机官能团(吡啶硫醚)的含"NS"杂原子的配体L,即2-((乙基硫代)甲基)吡啶。配体L与FeCl2反应后得到配合物[Fe(L)2Cl2],通过X-射线单晶衍射方法测定了它的晶体结构,并将该配合物作为对照物进行研究。结果表明:FeS@L-NSiG表现出更高的催化效果,几乎是FeC@L-NSiG的两倍。与材料FeC@L-NSiG相比,FeS@L-NSiG的催化效率上升是由于其表面上Fe(Ⅱ)中心含有更多的易离去配体(溶剂分子或水分子),从而使底物更容易接近金属中心。     

轴向配基对HRP模拟酶Hemin催化荧光及化学发光反应影响的研究

以氯化血红素作为辣根过氧化物酶（ＨＲＰ）的模拟物,对二十种氨基酸和其他含氮有机配体的轴向配位效应进行了研究。发现在氯化血红素催化的荧光和化学发光体系中,组氨酸和咪唑均使ｈｅｍｉｎ的催化活性显著提高,而酪氨酸,色氨酸,Ｌ－半胱氨酸及卤代烷基吡啶等具有淬灭效应。     

分子动力学研究亚铁血红素激活蛋白转录激活机理

以3种亚铁血红素激活蛋白(Heme activator protein, HAP)-DNA 复合物(野生型HAP1-wt, Ser63/Arg63突变HAP1-18 和 Ser63/Gly63突变HAP1-PC7)为对象对亚铁血红素激活蛋白的转录激活机理进行了分子动力学研究. 对3个复合物分子动力学轨迹的比较性分析显示, 涉及到上游活化序列(Upstream activation sequences, UAS)识别的蛋白质-DNA 相互作用分布与实验观测到的3种蛋白转录活性一致. 进一步对3个复合物进行柔性分析显示, 3个DNA分子具有相似的柔性, 而又有所不同, 特别在涉及UAS识别的N-端和Zn2Cys6结构域前部有明显的柔性差异. 蛋白质柔性的差别导致不同的蛋白质-DNA相互作用. 因此亚铁血红素激活蛋白的N-端和Zn2Cys6结构域前部的柔性大小能够调节亚铁血红素激活蛋白转录激活功能.     

CO and NO in medicine

The occurrence, role and consequences of CO and NO in biological systems are reviewed. This includes their syntheses by heme oxygenases and NO synthases, their biological targets and the physiological effects of their signals. The use of CO and NO gases in medicine are discussed and methods of delivery are illustrated with particular emphasis on the therapeutic properties of compounds that generate controlled amounts of NO and CO in vivo.     

Binding of YC-1 or BAY 41-2272 to soluble guanylyl cyclase induces a geminate phase in CO photolysis

Soluble guanylyl/guanylate cyclase (sGC), a heme-containing heterodimeric protein of approximately 150 kDa, is the primary receptor for nitric oxide, an endogenous molecule of immense physiological importance to animals. Recent studies have identified compounds such as YC-1 and BAY 41-2272 that stimulate sGC independently of NO binding, properties of importance for the treatment of endothelial dysfunction and other diseases linked to malfunctioning NO signaling pathways. We have developed a novel expression system for sGC from Manduca sexta (the tobacco hornworm) that retains the N-terminal two-thirds of both subunits, including heme, but is missing the catalytic domain. Here, we show that binding of compounds YC-1 or BAY 41-2272 to the truncated protein leads to a change in the heme pocket such that photolyzed CO cannot readily escape from the protein matrix. Geminate recombination of the trapped CO molecules with heme takes place with a measured rate of 6 x 10(7) s(-1). These findings provide strong support for an allosteric regulatory model in which YC-1 and related compounds can alter the sGC heme pocket conformation to retain diatomic ligands and thus activate the enzyme alone or in synergy with either NO or CO.     

Ligand migration in nonsymbiotic hemoglobin AHb1 from Arabidopsis thaliana

AHb1 is a hexacoordinated type 1 nonsymbiotic hemoglobin recently discovered in Arabidopsis thaliana. To gain insight into the ligand migration inside the protein, we studied the CO rebinding kinetics of AHb1 encapsulated in silica gels, in the presence of glycerol. The CO rebinding kinetics after nanosecond laser flash photolysis exhibits complex ligand migration patterns, consistent with the existence of discrete docking sites in which ligands can temporarily be stored before rebinding to the heme at different times. This finding may be of relevance to the physiological NO dioxygenase activity of this protein, which requires sequential binding of two substrates, NO and O2, to the heme.     

Theoretical density functional theory studies on interactions of small biologically active molecules with isolated heme group

We present ab-initio density functional theory studies on the interactions of small biologically active molecules, namely NO, CO, O(2), H(2)O, and NO(2) (-) with the full-size heme group. Our results show that the small molecule-iron bond is the strongest in carbonyl and the weakest in nitrite system. Trans influence induced by NO binding to the five-coordinate heme complex is shown. Nitric oxide in the resulting complex might be described as NO(-). The differences among the small ligands of XO type (CO, NO, O(2)), and their distant chemical behavior from H(2)O and NO(2) (-) ligands in binding to the Fe(II) ion, are shown. Moreover, the role of the heme ring as a reservoir of electrons in the studied complexes is invoked. The analysis of the parameters defining the iron-histidine bond indicates that this bond is longer and weaker in nitrosyl and carbonyl complexes than in the other systems. Our findings support the proposed mechanism of soluble guanylate cyclase (sGC) activation and suggest that the first step of sGC activation by CO may be the same as during the activation by NO. Obtained results are then compared with the data concerning smaller model of the heme, the porphyrin complexes, available in the literature.     

Binding Properties of CO,NO, and O2 to P450 Heme: a Density Functional Study

The structural and binding properties of diatomic molecules CO, NO and O2 to P450 heme were investigatedin two different models (labeled as M1 and M2) using density functional method at the B3LYP/6-31G(d)level. The e?ects of the serine residue near diatomic molecules XO were considered in the model M2. Theresults show that the serine residue near the heme enforced the binding of XO to heme. Frequency analysisindicates that the stretching vibrational frequency decreased as CO, NO, and O2 complex with heme.     

Alkylamine-ligated H93G myoglobin cavity mutant: a model system for endogenous lysine and terminal amine ligation in heme proteins such as nitrite reductase and cytochrome f

His93Gly sperm whale myoglobin (H93G Mb) has the proximal histidine ligand removed to create a cavity for exogenous ligand binding, providing a remarkably versatile template for the preparation of model heme complexes. The investigation of model heme adducts is an important way to probe the relationship between coordination structure and catalytic function in heme enzymes. In this study, we have successfully generated and spectroscopically characterized the H93G Mb cavity mutant ligated with less common alkylamine ligands (models for Lys or the amine group of N-terminal amino acids) in numerous heme iron states. All complexes have been characterized by electronic absorption and magnetic circular dichroism spectroscopy in comparison with data for parallel imidazole-ligated H93G heme iron moieties. This is the first systematic spectral study of models for alkylamine- or terminal amine-ligated heme centers in proteins. High-spin mono- and low-spin bis-amine-ligated ferrous and ferric H93G Mb adducts have been prepared together with mixed-ligand ferric heme complexes with alkylamine trans to nitrite or imidazole as heme coordination models for cytochrome c nitrite reductase or cytochrome f, respectively. Six-coordinate ferrous H93G Mb derivatives with CO, NO, and O(2) trans to the alkylamine have also been successfully formed, the latter for the first time. Finally, a novel high-valent ferryl species has been generated. The data in this study represent the first thorough investigation of the spectroscopic properties of alkylamine-ligated heme iron systems as models for naturally occurring heme proteins ligated by Lys or terminal amines.     

Ferric and ferrous iron in nitroso-myoglobin: computer simulations of stable and metastable States and their infrared spectra.

The binding of NO to iron is involved in the biological function of many heme proteins. Contrary to ligands like CO and O(2), which only bind to ferrous (Fe(II)) iron, NO binds to both ferrous and ferric (Fe(III)) iron. In a particular protein, the natural oxidation state can therefore be expected to be tailored to the required function. Herein, we present an ab initio potential-energy surface for ferric iron interacting with NO. This potential-energy surface exhibits three minima corresponding to eta(1)-NO coordination (the global minimum), eta(1)-ON coordination and eta(2) coordination. This contrasts with the potential-energy surface for Fe(II)-NO, which exhibits only two minima (the eta(2) coordination mode for Fe(II) is a transition state, not a minimum). In addition, the binding energies of NO are substantially larger for Fe(III) than for Fe(II). We have performed molecular dynamics simulations for NO bound to ferric myoglobin (Mb(III)) and compare these with results obtained for Mb(II). Over the duration of our simulations (1.5 ns), all three binding modes are found to be stable at 200 K and transiently stable at 300 K, with eventual transformation to the eta(1)-NO global-minimum conformation. We discuss the implication of these results related to studies of rebinding processes in myoglobin.     

Effect of strain in the proximal ligand on the binding of nitric oxide and carbon monoxide to chelated protoheme complexes

The binding of NO and CO to chelated protoheme-l-histidine methyl ester (HM-H), protoheme-glycyl-l-histidine methyl ester (HM-GH), and free protoheme (HM) has been studied in methanol-DMSO solution. In all cases, the NO adducts are five-coordinated, indicating that binding of NO occurs with displacement of the axial base, and confirms the strong negative trans effect exerted by NO in heme complexes, though it is found that the presence of strain in the iron-histidine bond of HM-H has a positive influence on NO binding, making it thermodynamically more favorable than for HM-GH. The equilibrium constants thus decrease in the series: HM > HM-H > HM-GH. In contrast to NO, CO has a positive trans effect, and therefore, an opposite trend is observed in the binding of this ligand to the heme complexes.     

A distal pocket Leu residue inhibits the binding of O2 and NO at the distal heme site of cytochrome c'

Cytochromes c' are pentacoordinate heme proteins with sterically hindered distal sites that bind NO and CO but do not form stable complexes with O(2). Removal of distal pocket steric hindrance via a Leu→Ala mutation yields favorable O(2) binding (K(d) ~49 nM) without apparent H-bond stabilization of the Fe-O(2) moiety, as well as an extremely high distal heme-NO affinity (K(d) ~70 fM). The native Leu residue inhibits distal coordination of diatomic ligands by decreasing k(on) as well as increasing k(off). The connection between distal steric constraints, k(off) values, and distal to proximal heme-NO conversion is discussed.