Photo and Magneto-Chemical Studies on Microstructure and Function of Active Sites

利用本项目研制的同步ESR和光学测量仪（ESRET），对典型酶的微观结构和活性位点的功能进行了光化学和磁化学研究。1) Fe (tpp) Cl作为血红素-Fe^<3+>蛋白的模型复合物。该配合物明显形成了铁（tpp）（OOR）的过氧化物加合物，这是几个酶促反应的关键中间体。ESR和吸收光谱显示了其形成的特征。2)以Co^<3+>-多胺和Co^<2+>-(SB)（SB: shift碱）为双加氧酶模型，研究了儿茶酚双加氧酶的反应机理。前一种配合物与儿茶酚形成二元配合物，然后加入O_2形成三元配合物。在后一种反应中，O_2首先与配合物形成氧加合物，并发生分子内电子转移反应。其次，儿茶酚作为底物被钴配合物氧化成半醌。3) Fe^<3+>-EDTA及其类似物与活性氧发生反应，是Fe- sod模型的典型例子。ESRET结果表明，该反应形成了两种中间体，一种是边型Fe^<3+>- o_2 ^<2->，另一种是Fe^<2+>- o_2 ^-。以这些中间体为探针，对SOD的反应机理进行了研究。

Photo- and magneto-chemical studies on microstructure and function of the active sites in typical enzymes have been carried out by using a simultaneous ESR and optical measurement apparatus (ESRET) developed by this project. 1) Fe (tpp) Cl was employed as a model complexes of heme-Fe^<3+> proteins. This complex showed a clear formation of a peroxide adduct of Fe (tpp)(OOR), which is a key intermediate to function as several enzymatic reaction. The ESR and absorption spectra exhibit characteristic features of its formation. 2) By using the Co^<3+>-polyamine and Co^<2+>-(SB)(SB : Shiff base) as models of dioxygenases we have examined reaction mechanisms of catechol dioxygenase reactions. The former complex formed a binary complex with catechols, followed by an addition of O_2 resulting in a ternary complex. In the latter O_2 first formed an oxygen adduct with the complex, and occurred an intramolecular electron transfer reaction. Secondly, catechol as a substrate was oxydized by the cobalt complex to semiquinone. 3) As a typical example of Fe-SOD model Fe^<3+>-EDTA and its analogs were reacted with active oxygen species. It was found by ESRET that two intermediates are formed : One is sideon type Fe^<3+>-O_2^<2-> and the other Fe^<2+>-O_2^-. By using these intermediates as probes of the recation, the reaction mechanism of the SOD was investigated.