Identification of a spin-coupled Mo(III) in the nitrogenase iron-molybdenum cofactor
Identification of a spin-coupled Mo(III) in the nitrogenase iron-molybdenum cofactor
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DOI：
10.1039/c4sc00337c
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发表时间：
2014-01-01
期刊：
影响因子：
8.4
通讯作者：
DeBeer, Serena
中科院分区：
文献类型：
--
作者：
Bjornsson, Ragnar;Lima, Frederico A.;DeBeer, Serena
固氮酶是一种复杂的酶，利用MoFe 7S 9 C簇催化氨的形成。最近发现了中心碳原子的存在，最终完成了活性位点的原子水平描述。然而，理解该机制的重要先决条件--总电荷、金属氧化态和电子结构尚不清楚。本文介绍了固氮酶的高能量分辨率荧光检测钼K边X射线吸收光谱。与已知氧化态的FeMo模型复合物的比较表明，固氮酶的FeMo辅因子中的Mo最好描述为Mo（III），与普遍接受的Mo（IV）分配相反。的氧化态分配支持的理论计算，揭示了一个不寻常的自旋耦合钼（III）网站的存在。虽然到目前为止还没有报道Mo（III）在生物学中出现，但这一建议与已知的用于N-2还原的均相Mo催化剂（其中Mo（III）化合物是N-2结合物种）提出了有趣的相似之处。它还需要在辅因子的Fe氧化态的重新分配。
Nitrogenase is a complex enzyme that catalyzes the formation of ammonia utilizing a MoFe7S9C cluster. The presence of a central carbon atom was recently revealed, finally completing the atomic level description of the active site. However, important prerequisites for understanding the mechanism - the total charge, metal oxidation states and electronic structure are unknown. Herein we present high-energy resolution fluorescence detected Mo K-edge X-ray absorption spectroscopy of nitrogenase. Comparison to FeMo model complexes of known oxidation state indicates that the Mo in the FeMo cofactor of nitrogenase is best described as Mo(III), in contrast to the universally accepted Mo(IV) assignment. The oxidation state assignment is supported by theoretical calculations, which reveal the presence of an unusual spin-coupled Mo(III) site. Although so far Mo(III) was not reported to occur in biology the suggestion raises interesting parallels with the known homogenous Mo catalysts for N-2 reduction, where a Mo(III) compound is the N-2-binding species. It also requires a reassignment of the Fe oxidation states in the cofactor.