EXAFS SPECTROSCOPIC STUDIES OF THE NIFE 'C-CLUSTER' IN CARBON MONOXIDE DEHYDROGE

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 细菌R. rubrum（Rr）和C.产氢菌（Ch）含有Ni一氧化碳脱氢酶（CODH），使它们能够在CO作为其唯一碳源上生长。Ni CODH的活性位点是所谓的“C簇”，这是一种新型的Ni-Fe-S中心，可以催化CO氧化为CO2。最近的X-射线晶体学已经表明，“C-簇”包括一个Ni配位到FeS 4单元，桥接到外部Fe位点。这是一个惊喜，因为之前的EXAFS分析排除了对称的NiFeS 4单元。然而，各种“C-簇”晶体结构显示出显着的差异与对方，而且，他们也显示出集群的异质性在一个给定的晶体的证据。我们有最近的EXAFS数据，显示证据的集群重新安排减少和/或CO结合。这意味着簇结构动态地重新排列，或者作为“活化”过程的一部分，或者作为其催化机制的一部分。我们建议使用EXAFS来调查的“C-簇”网站的结构变化的Rr和Ch CODH。这是对C-星系团进行全面光谱研究的一部分。我们计划研究已经：还原平衡; CO结合和抑制的酶。我们有可用的变体Rr CODH的活性位点残基已被修改，其中外部Fe被删除。我们也有Co-CODH和Zn-CODH，其中Ni被另一种过渡金属取代。我们相信，使用其他光谱，如EPR，FT-IR和共振拉曼作为对照，我们可以制备均匀的C-簇样品的EXAFS分析。这应该使我们能够参数化的C-集群结构动力学，并从那里了解基础集群化学，并最终催化循环的生物重要的酶系统。此外，新的生物无机化学发现可能会导致新的催化剂的发展。

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. The bacteria R. rubrum (Rr) and C. hydrogenoformans (Ch) contain a Ni carbon monoxide dehydrogenase (CODH) that enables them to grow on CO as their sole carbon source. The active site of Ni CODH is the so-called 'C-cluster' a novel Ni-Fe-S center that catalyzes the oxidation of CO to CO2. Recent X-ray crystallography has shown the 'C-cluster' to comprise a Ni coordinated to a FeS4 unit, bridged to an external Fe site. This was a surprise, as prior EXAFS analysis had excluded a symmetric NiFeS4 unit. However, the various 'C-cluster' crystal structures show significant differences with each other, and, they also show evidence of cluster heterogeneity within a given crystal. We have recent EXAFS data that shows evidence of cluster re-arrangement on reduction and/or CO binding. The implication is that the cluster structure dynamically rearranges, either as part of an "activation" process, or as part of its catalytic mechanism. We propose to use EXAFS to investigate the structural changes of the 'C-cluster' sites for Rr and Ch CODH. This is part of a comprehensive spectroscopic study on the C-cluster. We plan to study enzyme that has been: reductively poised; CO-bound and inhibited. We have available variants of Rr CODH where active site residues have been modified, one where the external Fe is deleted. We also have Co-CODH and Zn-CODH, where the Ni has been replaced by another transition metal. We are confident that, using other spectroscopies such as EPR, FT-IR and resonance Raman as controls, we can prepare homogeneous C-cluster samples for EXAFS analysis. This should enable us to parameterize the C-cluster structural dynamics and from there understand the underpinning cluster chemistry and eventually the catalytic cycle of this biologically important enzyme system. In addition, the novel bioinorganic chemistry uncovered could well lead to the development of novel catalysts.