SINGLE CRYSTAL XAS STUDIES ON O2 ACTIVATING HEME PROTEINS

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 我们建议使用溶液和单晶XAS光谱来研究参与O2结合的两种血红素蛋白。第一个研究将是细胞色素c过氧化物酶，它催化双氧水的两电子还原为水。过氧化氢的还原是通过形成两个高价的血红素中间体：化合物I和化合物II进行的。我们计划使用单晶Fe K边XAS和EXAFS来研究化合物I，以确定光还原的速度和EXAFS信号(特别是Fe-O键)的伴随变化。这些研究将扩展到CCP的化合物II，以了解这两个高价态在几何结构和电子结构上的差异。XAS数据将与DFT(密度泛函理论)和FeK-Pre-Edge Time DFT计算相耦合，这将有助于揭示CCP催化H_2O_2还原机理中形成的中间产物。在第二个研究中，我们建议使用Fe K-前边分析和含时密度泛函理论相结合的方法来研究氧合血红蛋白的电子结构。这些数据将与脱氧血红蛋白、高铁血红蛋白和血红素模型络合物相关联，以准确区分氧合血红蛋白中[(血红素)Fe-O2]物种的下列可能的电子构型：i)低自旋S=0FeII单态S=0O2，ii)中自旋S=1FeII三重态S=1O2(反铁磁性(AF)耦合)和iii)低自旋S=1/2FeIII S=1/2O2-(超氧化物)。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We propose to investigate two heme proteins involved in O2 binding using solution and single crystal XAS spectroscopy. The first study will be on cytochrome c peroxidase, which catalyzes the two-electron reduction of H2O2 to water. The reduction of H2O2 proceeds via the formation of two high-valent heme intermediates; compound I and compound II. We plan to study compound I using single crystal Fe K-edge XAS and EXAFS to determine the rate of photoreduction and the concomitant change in the EXAFS signal (specifically the Fe-O bond). These studies will be extended to compound II of CCP to understand differences in the geometric and electronic structure between the two high-valent states. The XAS data will be coupled to DFT (density functional theory) and Fe K-pre-edge time dependent-DFT calculations, which will help shed light on the intermediates formed in the catalytic mechanism of H2O2 reduction by CCP. In the second study we propose to investigate the electronic structure of oxyhemoglobin using a combination of Fe K-pre-edge analysis and time-dependent DFT calculations. The data will be correlated to deoxyhemoglobin, methemoglobin and heme model complexes to accurately distinguish between the following possible electronic configurations of the [(heme)Fe-O2] species present in oxyhemoglobin: i) low-spin S=0 FeII + singlet S=0 O2, ii) an intermediate-spin S=1 FeII + triplet S=1 O2 (antiferromagnetically (AF) coupled) and iii) a lowspin S=1/2 FeIII + S=1/2 O2 - (superoxide).