PULSED EPR STUDIES OF BIOLOGICAL MANGANESE CLUSTERS

我们建议利用脉冲EPR方法来研究结构 光系统II（PS）的四核Mn团簇及其功能 II）植物光合作用和Mn过氧化氢酶。 电子自旋回波包络技术 调制（ESEEM）和电子自旋回波-电子核 双共振（ESE-ENDOR）将用于检测核 磁核内部和附近的自旋跃迁 这些多核锰簇。高频ESE-ENDOR将 用于测量生物样品的55 Mn自旋跃迁 Mn簇合物和已知结构的合成模型化合物。 取向的PS II膜和PS II的单晶将是 研究了增强分辨率。这些实验将提供 关于这个重要催化位点的结构的新知识。 蛋白质与PS H和过氧化氢酶中的Mn簇的连接将是 探讨了底物和抑制剂分子的结合将是 表征了对于PS 11 Mn簇，实验将是每- 形成的特征的作用Ca 2+和Cl-，这是 氧释放化学中的重要辅因子。实验 将进行测试的假设，光合氧 演化是以金属自由基机制发生的， Mn簇和酪氨酸Yz。平行极化EPR信号 将用于检测Mn团簇的整数自旋信号。

We propose to utilize pulsed EPR methods to study the structure and function of the tetranuclear Mn cluster of Photosystem II (PS II) of plant photosynthesis and the Mn catalase enzyme. Specifically, the techniques of electron spin echo envelope modulation (ESEEM) and electron spin echo - electron nuclear double resonance (ESE-ENDOR) will be utilized to detect nuclear spin transitions of magnetic nuclei within and in close proximity to these multinuclear Mn clusters. High frequency ESE-ENDOR will be utilized to measure the 55Mn spin transitions of the biological Mn clusters and of synthetic model compounds of known structure. Oriented PS ll membranes and single crystals of PS ll will be studied for enhanced resolution. These experiments will provide new knowledge about the structure of this essential catalytic site. The protein ligation to the Mn clusters in PS H and catalase will be explored. The binding of substrate and inhibitor molecules will be characterized. For the PS ll Mn cluster, experiments will be per- formed to characterize the roles of Ca2+ and Cl-, which are essential cofactors in the oxygen evolution chemistry. Experiments will be performed to test the hypothesis that photosynthetic oxygen evolution occurs with a metalloradical mechanism, involving both the Mn cluster and tyrosine Yz. Parallel polarization EPR signals will be used to detect integer spin signals of the Mn clusters.