Spectroscopic Description of the E 1 State of Mo Nitrogenase Based on Mo and Fe X-ray Absorption and Mössbauer Studies
Spectroscopic Description of the E 1 State of Mo Nitrogenase Based on Mo and Fe X-ray Absorption and Mössbauer Studies
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基于 Mo 和 Fe X 射线吸收和穆斯堡尔研究的 Mo 固氮酶 E 1 态的光谱描述
DOI：
10.1021/acs.inorgchem.9b01951
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发表时间：
2019
影响因子：
4.6
通讯作者：
DeBeer, Serena
中科院分区：
文献类型：
--
作者：
Van Stappen, Casey;Davydov, Roman;Yang, Zhi-Yong;Fan, Ruixi;Guo, Yisong;Bill, Eckhard;Seefeldt, Lance C.;Hoffman, Brian M.;DeBeer, Serena
Mo氮化酶（N2ase）利用催化MoFe及其电子转移伙伴FeP这一双组分蛋白质体系将大气中的二氮（N2）还原为氨（NH3）。MoFe蛋白中包含的FeMo辅助因子作为该反应的催化中心，长期以来一直启发着以激活N2为导向的模型化学。这一化学领域在很大程度上依赖于Mo N2ase如何完成这一壮举的详细描述。了解Mo N2ase本身的反应机制是生物无机化学中最具挑战性的问题之一，因为其催化中间体的短暂性，即使不是不可能，也很难单独分离。这进一步加剧了FeP几乎必须减少原生MoFe，使得大多数传统的选择性减少方法无能为力。我们现在研究了MoFe催化循环的第一个基本中间体E1，它是通过低通量周转和辐射分解冷冻还原制备的，使用Mo Kα高能分辨率荧光检测和Fe k边缘部分荧光产率x射线吸收光谱技术的组合。结果表明，这一状态的形成是铁中心还原的结果，Mo保持氧化还原无罪。此外，利用Fe x射线吸收和57fe Mössbauer光谱，我们将先前报道的在低温还原条件下形成的独特物种与退火后形成的原生e1态相关联，证明了低温还原在研究MoFe催化中间体中的可行性。
Mo nitrogenase (N2ase) utilizes a two-component protein system, the catalytic MoFe and its electron-transfer partner FeP, to reduce atmospheric dinitrogen (N2) to ammonia (NH3). The FeMo cofactor contained in the MoFe protein serves as the catalytic center for this reaction and has long inspired model chemistry oriented toward activating N2. This field of chemistry has relied heavily on the detailed characterization of how Mo N2ase accomplishes this feat. Understanding the reaction mechanism of Mo N2ase itself has presented one of the most challenging problems in bioinorganic chemistry because of the ephemeral nature of its catalytic intermediates, which are difficult, if not impossible, to singly isolate. This is further exacerbated by the near necessity of FeP to reduce native MoFe, rendering most traditional means of selective reduction inept. We have now investigated the first fundamental intermediate of the MoFe catalytic cycle, E1, as prepared both by low-flux turnover and radiolytic cryoreduction, using a combination of Mo Kα high-energy-resolution fluorescence detection and Fe K-edge partial-fluorescence-yield X-ray absorption spectroscopy techniques. The results demonstrate that the formation of this state is the result of an Fe-centered reduction and that Mo remains redox-innocent. Furthermore, using Fe X-ray absorption and57Fe Mössbauer spectroscopies, we correlate a previously reported unique species formed under cryoreducing conditions to the natively formed E1state through annealing, demonstrating the viability of cryoreduction in studying the catalytic intermediates of MoFe.