XES AND XAS STUDIES OF SOLUBLE METHANE MONOOXYGENASE

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。 从生物学上讲，甲烷羟化是由产甲烷细菌中发现的甲烷单加氧酶(MMO)进行的。可溶形式的MMO利用双铁活性中心，该活性中心与氧气反应生成a-peroxo-Fe(III)Fe(III)物种(MMO-P)，然后生成Fe(IV)Fe(IV)物种(MMO-Q)，负责氧化甲烷。MMO催化循环的中间体一直是密集的实验和理论研究的主题。然而，MMO-Q和MMO-P一直没有得到结构表征，关于这些中间体的性质仍然存在许多问题。MMO-P的实验数据被用来论证顺式-MU-1，2-过氧基桥联模式，而计算研究则倾向于MU-2：2-O2核。对于MMO-Q来说，与EXAFS的2.5°Fe-Fe距离有利于双Mu-oxo Fe(IV)-Fe(IV)金刚石核结构。然而，没有振动数据支持任何假设的核心结构，并且MMO-P转化为MMO-Q的机制尚不清楚。这项研究旨在利用新的光谱方法来阐明甲烷羟化反应中这些关键中间体的电子结构。K-Beta X射线发射光谱被认为是对Fe2O2上价区的选择性探针，它可以提供氧键强度和结合方式的灵敏测量。这些数据将得到常规XAS数据的补充，并与光谱的DFT计算相关联。我们最初的研究将集中在表征良好的模型络合物上，然后将扩展到酶促中间体。这些研究的结果应该会为甲烷羟化的生物过程提供基本的见解。

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. 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.