Role of Phytochelatins on Metal Metabolism in Plants

1)采用Fmoc法合成了植物螯合素Phytochelatin。合成的粗产物经HPLC纯化、冻干后得到合成的PC-2，全过程收率为32%。2）Cd-PC复合物的结构分析用~ 1H-1H COSY、~（13）C-1H COSY、HMBC对PC-2的NMR谱进行了归属，结果表明，PC-2中的巯基在Cd-PC复合物的形成中起重要作用，酰胺基和羧基贡献较小。立体异构体的存在和它们之间的相互交换已被提出。从电子吸收光谱中我们推断出，结构随Cd-PC比例的变化而变化。在较低的Cd-PC比条件下，一个Cd原子以硫原子四面体构型结合两个PC分子。3）Cd-PC配合物的结构分析电子吸收光谱表明，Zn原子与PC分子以四面体的几何构型结合，与Zn：PC的比例无关。因此，两个巯基、酰胺基和/或羧基对络合物的形成有贡献。4）结论从动力学角度阐明了金属离子的结合。然而，复杂的涉及酸不稳定的硫化物在体内，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.