XES AND XAS STUDIES OF SOLUBLE METHANE MONOOXYGENASE

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心赠款提供。次级项目的主要支助 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 为子项目列出的总成本可能 表示子项目使用的中心基础设施的估计数量， NCRR赠款不直接向子项目或子项目工作人员提供资金。 在生物学上，甲烷的羟基化是由甲烷营养细菌中发现的甲烷单加氧酶（MMO）进行的。MMO的可溶形式利用二铁活性位点，其与分子氧反应以生成α-过氧-Fe（III）Fe（III）物质（MMO-P），然后生成Fe（IV）Fe（IV）物质（MMO-Q），其负责氧化甲烷。MMO催化循环的中间体一直是实验和理论研究的主题。然而，MMO-Q和MMO-P的结构表征，以及这些中间体的性质的许多问题仍然存在。MMO-P的实验数据已被用于论证顺式-mu-1，2-过氧桥接模式，而计算研究有利于mu-2：2-O2核心。对于MMO-Q，EXAFS的2.5 <$Fe-Fe距离有利于双-mu-氧代Fe（IV）-Fe（IV）金刚石核结构。然而，不存在振动数据来支持任何假定的核心结构，并且MMO-P转化为MMO-Q的机制是未知的。本研究的目的是利用新的光谱方法来阐明甲烷羟基化反应中这些关键中间体的电子结构。K-β X射线发射光谱提出作为一个选择性的探头的Fe 2 O2的上价区域，这应该提供一个灵敏的测量的氧键强度和结合模式。这些数据将补充传统的XAS数据和相关的DFT计算的光谱。我们的初步研究将集中在良好的特点模型复合物，然后将扩展到酶的中间体。这些研究的结果应该提供基本的见解甲烷羟基化的生物过程。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Biologically, the hydroxylation of methane is carried out by methane monoxygenases(MMO) found in methantrophic bacteria. The soluble form of MMO utilizes a diiron active site, which reacts with dioxygen to generate a -peroxo-Fe(III)Fe(III) species (MMO-P) and then an Fe(IV)Fe(IV) species (MMO-Q), which is responsible for oxidizing methane. The intermediates of the MMO catalytic cycle have been the subject of intense experimental and theoretical studies. However, MMO-Q and MMO-P have eluded structural characterization, and many questions about the nature of these intermediates remain. The experimental data for MMO-P have been used to argue for a cis-mu-1,2-peroxo bridging mode, while computational studies favor a mu-2:2-O2 core. For MMO-Q the 2.5 ¿ Fe-Fe distance from EXAFS favors a bis-mu-oxo Fe(IV)-Fe(IV) diamond core structure. However, no vibrational data exist to support any of the postulated core structures and the mechanism for conversion of MMO-P to MMO-Q is unknown. The proposed research is aimed at elucidating the electronic structure of these key intermediates in methane hydroxylation by utilizing new spectroscopic methods. K-Beta x-ray emission spectroscopy is proposed as a selective probe of the Fe2O2 upper valence region, which should provide a sensitive measure of the oxygen bond strength and the binding mode. These data will be complemented by conventional XAS data and correlated to DFT calculations of the spectra. Our initial studies will focus on well characterized model complexes and will then be extended to the enzymatic intermediates. The results of these studies should provide fundamental insights into the biological process of methane hydroxylation.