Role of Phytochelatins on Metal Metabolism in Plants

1)植物螯合素合成采用Fmoc法合成植物螯合素。合成的粗产物经高效液相色谱纯化、冻干后合成PC-2，全流程产率为32%。将PC-2与裂糖酵母（Schizosaccharomyce pombe）中分离得到的PC-2的保留时间和NMR谱进行了比较，两者一致。2) Cd-PC配合物的结构分析。PC-2的核磁共振波谱信号通过1H-1H COSY、13C-1H COSY、HMBC进行分配。认为PC-2中巯基对Cd-PC复合物的形成起重要作用，中间基和羧基的作用较小。提出了立体异构体的存在和它们之间的相互交换。从电子吸收光谱中，我们推导出结构随Cd-PC比的变化。在Cd-PC比较低的条件下，一个Cd原子与两个在Cd周围具有硫原子四面体结构的PC分子结合。随着Cd: PC比的增加，四面体结构由于羧基或氨基的捐赠而被打乱。3) Cd-PC配合物的结构分析电子吸收光谱表明，锌原子与PC分子结合，其几何形状与锌与PC的比值无关，为四面体。因此，两个硫醇、中间和/或羧基对络合物的形成有贡献。结论从动力学角度阐明了金属离子的结合。然而，该络合物涉及体内酸性不稳定的硫化物，因此，包括硫化物的分析将是必要的。

1) PHYTOCHELATIN SYNTHESISPhytochelatin were synthesized by Fmoc method. The crude product synthesized was purified by HPLC,lyophilized and then synthetic PC-2 was obtained with the yield through the whole process of 32%. The retention time and NMR spectrum was compared to PC-2 which was induced in fission yeast, Schizosaccharomyce pombe, and purified from it and these are concluded to be identical.2) STRUCTURAL ANALYSIS of Cd-PC COMPLEXThe signals in NMR spectrum of PC-2 were assigned by 1H-1H COSY,13C-1H COSY,HMBC.It has been suggested that thiol groups in PC-2 plays an important role formation of Cd-PC complex, amid and carboxy groups contributing with smaller extent. The presence of stereoisomers and the mutural interchanges between them have been suggested. We have deduced from the electronic absorption spectra that the structures change with Cd-PC ratio. Under the conditions of lower Cd-PC ratio, a Cd atom binds two molecules of PC with tetrahedral configuration of sulfur atoms around Cd. The tetrahedral structure has been shown to be distored by donation of carboxy or amino group when Cd : PC ratio increased.3) STRUCTURAL ANALYSIS of Cd-PC COMPLEXIt has been indicated from electronic absorption spectra that a Zn atom bind to a PC molecule with a giometry of tetrahedral irespective of the Zn : PC ratio. Two thiols, and amids and/or carboxyl groups, therefore, were contribution to the formation of the complex.4) ConclusionBinding of metal ions has been clarified from dynamic aspect. However, the conplex involves acid labile sulfide in vivo, so that the analysis including the sulfide will be necessary.