Evolution of a Model of Nitrogenase Active-center and Mechanism of Nitrogenase Gataivsis
- 化学化工－已发表论文 
[中文摘要]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。[英文摘要]A twin-sited-dicubane-type-cluster structural model of nitrogenase active-center, [S*Fe3S2*(L)]Mo[(L')S2*Fe3S*], has been proposed, L and L' being two labile ligands, such as N2, NH3, H,or H2O. This model is a logical evolution of the twin-sited-monocubane-type-clunter structural model, Fe2S2*Mo2O2, and the twin-sited-tricubane-type-cluster structural model, Fe2S2*(L)(L')Mo2[S3*Fe3S*]2, previously proposed by us. The twin-sited-cubane-type-duster structural feature common to all the three models and the end-on-plus-double-side-on coordination activation of N2,a-acetylenes,alkyl cyanides and isocyanides on the trinuclear active-center have been inferred mainly from the known reactions of nitrogenase with the various types of substrates and CO inhibitor regarded as chemical probes,and from the principles of coordination catalysis;whereas revision of previous models with regard to the micro-environments of each molybdenum ion and the nature of the triunclear active-center(whether it is 2Mo-1Fe,or 1Mo-2Fe)have been made by reference to recent progresses on nitrogenase research reported by many laboratories.The twin-sited-dicubane-type-cluster structural model(with 1 Mo111(IV))is in accord with the EPR and Moessbauer spectra of nitrogenase and FeMo-co recently obtained and interpreted by Orme-Johnson and Munck.It also gives better mechanistic explanations for the enzyme-catalyzed reactions of all the known nitrogenase substrates and the charac-teristic behavior of CO as a selective inhibitor of nitrogenase.A brief,further discussion of the mechanism of ATP-driven electron and proton transports is also given.