胆碱酯酶催化反应的量子化学研究：残基作用对乙酰胆碱构象及其水解…

采用量子化学ＳＣＦ ＬＣＡＯ－ＭＯ ＭＮＤＯ和ＣＮＤＯ／２方法，考查了胆碱酯酶活性基因的存在对底物乙酰胆碱的构馁稳定性的影响。同时分析了活性基因作用下乙酰胆碱的水解部位化学键强度、净电荷分布等的相对变化规律，探讨了活性构象和稳定构象的联系。     

他克林及其类似物抑制乙酰胆硷酯酶机理的理论研究

用ＭＮＤＯ半经验法，计算了乙酰胆碱酯酶抑制剂他克林及其类似物的优化构型、前线轨道，电荷分布。并以这些量子化学参数讨论了它们抑制ＡＣｈＥ的机制。认为他克林嵌入ＡＣｈＥ的苏丙氨酸（Ｆ－３３０）和色氨酸（Ｗ－８４）之间，而形成一个“三明治”式夹心结构。同时他克林喹啉环上的氮和组氨酸－４４０的羰基形成氢键，使ＡＣｈＥ活性中心的构象改变而使其活性降低或失活。     

两性纤维素接枝共聚物的合成研究

采用ＫＭｎＯ４／Ｈ２ＳＯ４氧化还原引发体系,首次将羧甲基纤维素（ＣＭＣ）与二甲基二烯丙基氯化铵（ＤＭＤＡＡＣ）进行接枝聚合,制备了一系列分子中同时含有阴离子羧甲基和阳离子季铵基团的两性纤维素接枝共聚物．研究了ＣＭＣ取代度、ＤＭＤＡＡＣ加量、ＫＭｎＯ４用量和Ｈ２ＳＯ４浓度对接枝共聚的影响,并对其聚合反应机理作了探讨     

水分子与α（1→4）连接半乳糖醛酸间氢键的形成及其对构象的影响

采用量子化学ＳＣＦＬＣＡＯ—ＭＯＣＮＤＯ／２的方法，对水分子在不同位置与二聚半乳糖醛酸形成的氢键体系进行了探讨．在端位—ＯＨ上形成氢键比在—ＣＯＯＨ位形成氢键更为有利．进一步分析了水分子的氢键作用对二聚半乳糖醛酸的稳定构象，水解易于发生的可能构象的影响．     

水分子与α（1→4）连接半乳糖醛酸间氢链的形成及其对构象的影响

采用量子化学ＳＣＦ ＬＣＡＯ－ＭＯ ＣＮＤＯ／２的方法，对水分子在不同位置与二聚半乳糖醛酸形成的氢键体系进行了探讨，在端位－ＯＨ上形成氢键比在－ＣＯＯＨ位形成氢键更为有利，进一步分析了水分子的氢键作用对二聚半乳糖醛酸的稳定构象，水解易于发生的可能构象的影响。     

载体的酸碱特性对Ni－Cu催化剂上CO加氢性能的影响

本文采用ＸＲＤ，ＴＰＲ和以Ｈ２，ＣＯ为探针分子的ＴＰＤ—ＭＳ，ＴＰＳＲ－ＭＳ技术研究了Ｎｉ－ＣＵ合金负载于氧化物ＳｉＯ２，ＭｇＯ和γ－Ａｌ２Ｏ３上的性质变化，以及对ＣＯ加氢反应性能的影响。实验结果表明，各种载体对于负载于其上的活性组分均具有良好的分散性能；ＳｉＯ２对金属相的结构和电子状态不产生影响，而γ－Ａｌ２Ｏ３和ＭｇＯ对金属相则有不同程度的影响，这种相互作用主要表现在活性组分对Ｈ２和ＣＯ吸附能力的变化和ＣＯ加氢的活性和选择性的变化上。     

水稻幼苗超氧物歧化酶同工酶的研究

应用聚丙烯酰胺凝胶垂直平板电泳对水稻幼苗ＳＯＤ同工酶进行了研究。结果表明，４个品种的水稻幼苗的均含有６种ＳＯＤ同工酶，其中５种为Ｃｕ．Ｚｎ－ＳＯＤ，一种为Ｍｎ－ＳＯＤ，未发现Ｆｅ－ＳＯＤ．Ｃｕ．Ｚｎ－ＳＯＤ活性占ＳＯＤ总活性的９０％左右，Ｍｎ－ＳＯＤ占１０％左右，品种间同酶类型，酶活性无明显差异。     

亚甲二醇二硝酸酯构型和电子结构的ab initio研究

采用量子化学中的从头计算（ａｂｉｎｉｔｉｏ）方法，在ＨＦ／３－２１Ｇ和ＨＦ／６－３１Ｇ＊水平上分别计算研究了亚甲二醇二硝酸酯（ＭＧＤＮ）的旋转构象和电子结构，计算所得ＭＧＤＮ绕Ｃ—Ｏ键旋转的能垒较低（约６ｋＪ／ｍｏｌ），其平面构象的能量最高．能量最低的构象（亦即最稳定构型或平衡几何构型）的２个酯基均绕Ｃ—Ｏ键旋转７７．４°．不同构型的电荷分布差异较小．     

SOD模型化合物对油菜幼苗抗寒性的影响

用不同浓度的ＳＯＤ模型化合物以喷洒和浸民喷洒相结合两种方式处理油菜，研究ＳＯＤＭＣ对油菜幼苗抗寒性的影响，结果表明，在一定范围内，随着ＳＯＤＭＣ处理浓度的增加，两咱处理的幼苗ＳＯＤ活性、叶绿素含量均随之增高，而电导率随之降低，过氧化物酶（ＰＯＤ）活性略有下降，且浸种与喷洒相结合的处理方式比喷洒的效果好，由此可认为：用ＳＯＤＭＣ处理幼苗可在一定程度上提高油菜幼苗的抗寒性，减轻低温胁迫对膜的损伤。     

有机金属化合物中二级化学键的理论研究（Ⅵ）：——二级化学键生 …

应用半径经验分子轨道（ＭＯＰＡＣ７．０软件包中ＡＭ１和ＰＭ３）方法，对一些有机金属汞化合物进行了探讨和研究。通过总能量和生成熟的比较可知，由于分子内的二级化学链的生成，分子ｃｉｓ－ＨｌＨｇＣＨＣＨＣｌ和ｏ－Ｃ６Ｈ４ＨｇＣｌ２的能量较低，更稳定。对于含Ｐｈ－和ＣＮ－基团的一系列有机汞化合物，通过计算机其内旋转能垒中的初始构象和能谷构象可知，由于Ｈｇ与Ｐｈ－和－ＣＮ－之间的二级化学键的生成，其初始构象     

胆碱酯酶催化反应的量子化学研究——氧化对组氨酸、丝氨酸残基间氢迁移的影响

考虑到氧化对一些酶、核酸、细胞膜的生物活性丧失起着较大的作用,用量子化学半经验 CNDO/2法,从理论上探讨了胆碱酯酶中的组氨酸、丝氨酸残基间的氢键形成、氢迁移过程受氧化影响的大小,给出一些有益的信息。     

胆碱酯酶催化反应的量子化学研究——底物对组氨酸、丝氨酸残基间氢迁移的影响

本文考虑到底物的影响,对胆碱酯酶酯解部位的组氨酸、丝氨酸等残基问的氢键问题,继前文进行了深入的探讨,用量子化学理论进一步阐明乙酰胆碱酶催化水解反应的机理.指出丝氨酸残基的羟基在进攻底物的过程中逐步把氢原子转移给组氨酸残基.     

Acetylcholine analogue stimulates DNA synthesis in brain-derived cells via specific muscarinic receptor subtypes

Little is known about the factors which regulate the growth and development of the mammalian brain. Although proliferation of neuronal cells ceases relatively early in development, certain types of glial cells proliferate and differentiate mainly perinatally. In the perinatal period, the ability of acetylcholine to stimulate phosphoinositide (PI) hydrolysis in brain reaches peak levels, and indeed the stable acetylcholine analogue carbachol can stimulate PI hydrolysis of primary neonatal astroglial cells. As PI hydrolysis is thought to be important in the regulation of cell proliferation, we investigated whether cellular DNA synthesis can be induced by carbachol. Our results show that carbachol stimulates DNA synthesis via muscarinic acetylcholine receptors (mAChRs), in primary astrocytes derived from perinatal rat brain, in an age-dependent fashion. Carbachol is also mitogenic in certain brain-derived astrocytoma and neuroblastoma cell lines, as well as in chinese hamster ovary (CHO) cells expressing recombinant muscarinic receptors. DNA synthesis is strongly activated by carbachol in those brain-derived cell lines and transfected CHO cells that express mAChR subtypes which activate PI hydrolysis efficiently, and poorly activated in cells expressing mAChR subtypes which only weakly activate PI hydrolysis. These results strongly support a role for acetylcholine in regulating astroglial cell growth in the developing brain, and indicate that the specificity of acetylcholine-induced cell proliferation may be determined by the expression of those mAChR subtypes which activate PI hydrolysis.     

Chaperonin-mediated protein folding at the surface of groEL through a 'molten globule'-like intermediate.

Folding of two monomeric enzymes mediated by groE has been reconstituted in vitro. The groEL protein stabilizes the polypeptides in a conformation resembling the 'molten globule' state. Mg-ATP and groES then promote the acquisition of ordered tertiary structure at the surface of groEL. Folding requires the hydrolysis of about 100 ATP molecules per protein monomer. This active process of surface-mediated chain folding might represent a general mechanism for the formation of protein structure in vivo.     

Subcellular patterns of calcium release determined by G protein-specific residues of muscarinic receptors.

Calcium release from intracellular stores is a point of convergence for a variety of receptors involved in cell signaling. Consequently, the mechanism(s) by which cells differentiate between individual receptor signals is central to transmembrane communication. There are significant differences in timing and magnitude of Ca2+ release stimulated by the m2 and m3 muscarinic acetylcholine receptors. The m2 receptors couple to a pertussis toxin-sensitive G protein to activate phosphatidyl inositol hydrolysis weakly and to stimulate small, delayed and oscillatory chloride currents. In contrast, m3 receptors potently activate phosphatidyl inositol hydrolysis and stimulate large, rapid and transient chloride currents by a pertussis toxin-insensitive G protein pathway. Using confocal microscopy, we now show that the m2- and m3-coupled Ca2+ release pathways can also be spatially distinguished. At submaximal acetylcholine concentrations, both receptors stimulated pulses of Ca2+ release from discrete foci in random, periodic and frequently bursting patterns of activity. But maximal stimulation of m2 receptors increased the number of focal release sites, whereas m3 receptors invariably evoked a Ca2+ wave propagating rapidly just beneath the plasma membrane surface. Analysis of pertussis toxin sensitivity and hybrid m2-m3 muscarinic acetylcholine receptors confirmed that these Ca2+ release patterns represent distinct cell signalling pathways.     

胆碱脂酶催化反应的量子化学研究——氨基酸残基间氢键问题的计算与讨论

本文对胆碱脂酶脂解部位的组氨酸、丝氨酸等残基间的氢键问题做了CNDO/2的量子化学计算,从理论上讨论了乙酰胆碱酶催化水解反应中谁作为亲核基团向底物进攻的问题,得到一些有益的结果。     

Nucleotide-dependent bending flexibility of tubulin regulates microtubule assembly

The atomic structure of tubulin in a polymerized, straight protofilament is clearly distinct from that in a curved conformation bound to a cellular depolymerizer. The nucleotide contents are identical, and in both cases the conformation of the GTP-containing, intra-dimer interface is indistinguishable from the GDP-containing, inter-dimer contact. Here we present two structures corresponding to the start and end points in the microtubule polymerization and hydrolysis cycles that illustrate the consequences of nucleotide state on longitudinal and lateral assembly. In the absence of depolymerizers, GDP-bound tubulin shows distinctive intra-dimer and inter-dimer interactions and thus distinguishes the GTP and GDP interfaces. A cold-stable tubulin polymer with the non-hydrolysable GTP analogue GMPCPP, containing semi-conserved lateral interactions, supports a model in which the straightening of longitudinal interfaces happens sequentially, starting with a conformational change after GTP binding that straightens the dimer enough for the formation of lateral contacts into a non-tubular intermediate. Closure into a microtubule does not require GTP hydrolysis.     

Structure of the Sec23/24-Sar1 pre-budding complex of the COPII vesicle coat

COPII-coated vesicles form on the endoplasmic reticulum by the stepwise recruitment of three cytosolic components: Sar1-GTP to initiate coat formation, Sec23/24 heterodimer to select SNARE and cargo molecules, and Sec13/31 to induce coat polymerization and membrane deformation. Crystallographic analysis of the Saccharomyces cerevisiae Sec23/24-Sar1 complex reveals a bow-tie-shaped structure, 15 nm long, with a membrane-proximal surface that is concave and positively charged to conform to the size and acidic-phospholipid composition of the COPII vesicle. Sec23 and Sar1 form a continuous surface stabilized by a non-hydrolysable GTP analogue, and Sar1 has rearranged from the GDP conformation to expose amino-terminal residues that will probably embed in the bilayer. The GTPase-activating protein (GAP) activity of Sec23 involves an arginine side chain inserted into the Sar1 active site. These observations establish the structural basis for GTP-dependent recruitment of a vesicular coat complex, and for uncoating through coat-controlled GTP hydrolysis.