基于氨基作为质子迁移桥梁的蛋氨酸分子旋光异构机理

采用密度泛函理论的B3LYP方法和微扰理论的MP2方法,研究两种最稳定构型的蛋氨酸分子(Met)基于氨基作为质子迁移桥梁的旋光异构反应.结果表明:基于氨基作为质子迁移桥梁的蛋氨酸分子旋光异构反应有2条通道a和b;构型1的主反应通道为通道a,决速步骤为第1基元反应,自由能垒为264.2kJ/mol,由质子从手性C直接向氨基N迁移的过渡态产生;构型2的主反应通道也为通道a,决速步骤为第2基元反应,自由能垒为266.1kJ/mol,由羧基异构后质子从手性C向氨基N迁移的过渡态产生;两种构型的Met分子旋光异构速控步骤的反应速率常数分别为3.04×10~(-34),1.41×10~(-34) s~(-1).     

甲硒氨酸耐热邻苯二酚2,3双加氧酶的高表达和分离纯化

甲硒氨酸多波长反常散射法是国际上９０年代发展的蛋白质晶体结构测定的新方法,该法得以实施的首要一步是获得硒取代（硫）的高纯蛋白质。通过亚克隆将编码耐热邻苯二酚２,３双加氧酶（简称ＴＣＴＤ）的基因ＰＨＥＢ克隆至表达载体ｐＲＳＥＴ,得到了高表达质粒ｐＲＳＥＴ－ＰＨＥＢ,转入Ｍｅｔ缺陷的菌株Ｂ８３４ＤＥ３。通过诱导表达和分离纯化得到了甲硒氨酸参入的ＴＣＴＤ。经质谱测定发现ＴＣＴＤ的所有７个甲硫氨酸都被甲硒     

鸣禽间脑听觉卵圆核壳区脑啡肽的免疫组织化学？…

应用尼氏染色及脑啡肽免疫组织化学方法研究了鸣禽白腰文鸟（Ｌｏｎｃｈｕｒａ ｓｔｒｉａｔａ）间脑听觉中－卵圆核（ｎ．Ｏｖｏｉｄａｌｉｓ Ｏｖ）中心核及其壳区（ｓｈｅｌｌ）的形态学特征,再应用神经示踪剂ＢＤＡ（ｂｉｏｔｉｏｎｙｌａｔｅｄ ｄｅｘｔｒａｎ ａｍｉｎｅ）对壳区的神经投射了研究,结果发现（１）脑啡肽免疫组织方法尼氏染色更能区分中心核及壳区,仅Ｏｖ壳区存在脑啡肽纤维或细胞,而忠订户站不存在;     

《论语》“子见南子”章正诂

在《论语·雍也》篇中＂子见南子＂一章里,夫子＂矢辞＂中的＂否＂、＂厌＂二字的读音直接影响着本章训诂的准确性。历代学者对这一章的翻译,或主观上强改字意,或辗转意译附会旧说,究其根源,就在于忽略了＂否＂、＂厌＂二字的读音。通过研究,在＂子见南子＂章里,＂否＂字正音念＂pǐ＂,＂厌＂字正音念＂yā＂。而本章的正确释义是：夫子见过南子,子路不高兴。夫子对子路发誓说：＂我如果心思不正,上天惩罚我!上天惩罚我!＂     

Crystallographic Studies of Cephalosporin Acylase from Pseudomonas sp. Strain 130

The cephalosporin acylases are a group of enzymes that hydrolyze cephalosporin C and/or glutaryl 7-aminocephalosporanic acid to produce ?-aminocephalosporanic acid. The cephalosporin acylase from Pseudomonas sp. strain 130 was crystallized in two different forms suitable for structural studies. A tetragonal crystal form diffracted to 0.24 nm belonged to the space group P41212. There was one αβ heterodimer per asymmetric unit. A second crystal form diffracted to 0.21nm belonged to the space group P21. There was four αβ heterodimers per asymmetric unit. The tetragonal crystal structure of CA-130 was determined using the multiwavelength anomalous diffraction method and the P21 crystal structure was then determined using the molecular replacement method.     

Biological functions and signaling of a transmembrane semaphorin,CD100/Sema4D

The semaphorin proteins were identified originally as axonal guidance factors functioning during neuronal development. In addition to this function, several semaphorins play diverse roles outside the nervous system. The class 4 semaphorin CD100/Sema4D, which utilizes plexin-B1 and CD72 as receptors, exerts important biological effects on a variety of cells, including the neuronal, epithelial and immune cells. Here, we review recent advances exploring the molecular mechanisms governing the biological functions of CD100/Sema4D.Received 1 July 2003; received after revision 25 July 2003; accepted 29 July 2003