NEW STRUCTURAL INSIGHTS INTO THE IRON MOLYBDENUM COFACTOR FROM AZOTOBACTER-VINELANDII NITROGENASE THROUGH SULFUR-K AND MOLYBDENUM-L X-RAY ABSORPTION-EDGE STUDIES
NEW STRUCTURAL INSIGHTS INTO THE IRON MOLYBDENUM COFACTOR FROM AZOTOBACTER-VINELANDII NITROGENASE THROUGH SULFUR-K AND MOLYBDENUM-L X-RAY ABSORPTION-EDGE STUDIES
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DOI：
10.1021/ja00220a013
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发表时间：
1988-06-08
影响因子：
15
通讯作者：
HODGSON, KO
中科院分区：
文献类型：
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作者：
HEDMAN, B;FRANK, P;HODGSON, KO
利用x射线吸收边和近边光谱（以下简称XANES）在硫K和钼L3和L2吸收边研究了从固氮菌vinelandii MoFe蛋白中分离的FeMo辅因子（FeMo -co）中硫和钼的电子和结构性质。相对于x射线吸收边缘在高能量（例如，钼K边缘在20 keV时的几个电子伏）的分辨率相对较差，2.5-3.0 keV区域的分辨率显著提高（例如，硫K边缘在2.47 keV时的0.5 eV），导致更多的边缘结构，对电子和结构环境的变化具有更高的灵敏度。为了记录低能稀释样品的光谱，提出了一种利用波动磁体高通量同步辐射的实验方法。XANES光谱记录了FeMo-co的氧化（ox）和半还原（s-r）形式，以及一些含钼和硫的无机配合物的比较。为了消除二亚砜及其分解产物和其他未结合小分子对FeMO-co光谱的干扰，开发了厌氧柱层析纯化方法。因此，可以记录氧化形式的无二硫代盐的FeMo-co的光谱。结果表明，除了桥接硫化物外，还存在一种前所未有的与FeMo-co结合的氧化形式的硫。分析表明，该物种与结合的硫代硫酸盐具有密切的对应关系。氯化物在FeMo-co结扎过程中不起作用。最后，通过对几种Mo-Fe-S簇的氧化和半还原的FeMo-co态的钼L边和硫K边进行比较，发现钼的氧化态在氧化还原过程中是不变的。本文的研究结果为FeMo-co的提纯提供了一种新的方法，并对二亚砜及其分解产物在萃取机理和FeMo-co性能中的作用提出了一些重要的问题。
The electronic and structural nature of sulfur and molybdenum in the FeMo cofactor (FeMO-co) isolated from Azotobacter vinelandii MoFe protein has been studied by X-ray absorption edge and near-edge spectroscopy (referred to herein collectively as XANES) at the sulfur K and molybdenum L3 and L2 absorption edges. In contrast to the relatively poor resolution found for X-ray absorption edges at higher energies (e.g., several electronvolts at the molybdenum K edge at 20 keV), resolution in the 2.5-3.0-keV region is significantly improved (e.g., 0.5 eV at the sulfur K edge at 2.47 keV), resulting in more edge structure with higher sensitivity to changes in electronic and structural environment. In order to record spectra from dilute samples at these low energies, an experimental method that takes advantage of the higher flux synchrotron radiation from an undulator magnet has been developed. XANES spectra hve been recorded for FeMo-co in the oxidized (ox) and semireduced (s-r) forms and, for comparison, a number of inorganic complexes containing molybdenum and sulfur. To remove the interference of dithionite, its decomposition products, and other small unbound molecules from the FeMO-co spectrum, an anaerobic column chromatographic method of purification has been developed. The spectrum of dithionite-free FeMo-co in the oxidized form could thus be recorded. The results show that, in addition to the bridging sulfides, an unprecedented, oxidized form of sulfur bound to FeMo-co is present. Analysis reveals that the species shows a close correspondence with bound thiosulfate. It is also shown that chloride plays no part in ligation of FeMo-co. Finally, by comparison of both the molybdenum L and sulfur K edges of the oxidized and semireduced FeMo-co states with several Mo-Fe-S clusters, it is found that the oxidation state of molybdenum is unchanged upon redox. The results reported herein demonstrate a new method for FeMo-co purification and raise some important questions about the role of dithionite and its decomposition products in both the mechanism of extraction and the properties of FeMo-co.