HALIDE XAS STUDIES OF PHOTOSYNTHETIC WATER OXIDATION COMPLEX

光系统II（PS II）的放氧复合物（OEC）在植物中的分布 绿色植物、藻类和蓝细菌包含一个由四个 锰原子作为光诱导氧化的催化位点， 水变成氧气 锰K边X射线吸收光谱（XAS） 研究已被用来帮助阐明这种活性的结构， 位置以及Mn离子周围的电子环境， OEC积累氧化当量。 尽管氯化物是 被鉴定为光合放氧所需的辅因子 五十多年前，氯辅因子结合的位置 网站仍然未知。 因此，需要探测卤化物位点 直接和澄清其可能的接近锰簇。 这 一项提案寻求应用X射线吸收近边缘光谱学 （XANES）和扩展的X射线吸收精细结构（EXAFS）， PS II膜中的氯边缘，以确定Cl-是否结合 直接作用于Mn，及其在光合水机制中的作用 氧化 溴化物和碘化物可以用一些（尽管 抑制）OEC活性的保留，从而支持实验 使用Br-和I-取代的PS II膜包括在 实验计划

The oxygen-evolving complex (OEC) of Photosystem II (PS II) in green plants, algae, and cyanobacteria contains a cluster of four manganese atoms as the catalytic site of photo-induced oxidation of water to oxygen. Manganese K-edge X-ray absorption spectroscopy (XAS) studies have been used to help elucidate the structure of this active site as well as the electronic environment around the Mn ions as the OEC accumulates oxidative equivalents. Although chloride was identified as a required cofactor for photosynthetic oxygen evolution over fifty years ago, the location of the chloride cofactor binding site is still unknown. It is thus desirable to probe the halide site directly and clarify its possible proximity to the Mn cluster. This proposal seeks to apply x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS) at the chlorine edge in PS II membranes to determine whether Cl- is bound directly to Mn, and its role in the mechanism of photosynthetic water oxidation. Bromide and iodide can be substituted with some (albeit subdued) retention of OEC activity, and thus supporting experiments using Br- and I-- substituted PS II membranes are included in the experimental program.