The One-Electron Reduced Active-Site FeFe-Cofactor of Fe-Nitrogenase Contains a Hydride Bound to a Formally Oxidized Metal-Ion Core
The One-Electron Reduced Active-Site FeFe-Cofactor of Fe-Nitrogenase Contains a Hydride Bound to a Formally Oxidized Metal-Ion Core
复制标题
Fe-固氮酶的单电子还原活性位点 FeFe-辅因子含有与形式氧化的金属离子核心结合的氢化物
DOI：
10.1021/acs.inorgchem.2c00180
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发表时间：
2022
影响因子：
4.6
通讯作者：
Hoffman, Brian M.
中科院分区：
文献类型：
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作者：
Lukoyanov, Dmitriy A.;Harris, Derek F.;Yang, Zhi-Yong;Pérez-González, Ana;Dean, Dennis R.;Seefeldt, Lance C.;Hoffman, Brian M.
固氮酶活性位点辅因子必须在N2结合和还原之前积累4 e-/4 H+（E4（4 H）状态）。早期的研究表明，E4（4 H）状态将还原当量储存为两个电子，辅因子金属离子核心形式上处于其静息态氧化还原水平。这导致了这样的理解，即N2结合与产生H2的两个质子的还原消除机械地耦合。已获得2 e-/2 H+（E2（2 H））的状态相应地包含一个具有静止态核心氧化还原能级的氢化物。余因子如何适应第一个e-/H+（E1（H）态）的增加是未知的。Fe-固氮酶FeFe-辅因子用于解决这个问题，因为它在E1（H）状态下具有EPR活性，不像Mo-固氮酶的FeMo-辅因子，因此允许通过EPR光谱进行表征。Fe固氮酶的E1（H）态具有S = 1/2 EPR谱，g = [1.965，1.928，1.779]。这种状态是光活性的，并且在1/2 K低温腔内，450 nm光解转化为新的并且同样光活性的S = 1/2状态（表示为E1（H）*），g = [2.009，1.950，1.860]，这导致光稳态，其中E1（H）* 在145 K以上弛豫为E1（H）。12 K E1（H）/E1（H）* 光互变产生2.4的H/D动力学同位素效应。这些观察结果表明，除了第一个e-/H+的Fe固氮酶的FeFe-辅因子产生铁结合的氢化物，而不是硫结合的质子。因此，相对于静止状态，簇金属离子核心形式上是单电子氧化的。有人建议，这一行为适用于所有三种固氮酶同工酶。
The nitrogenase active-site cofactor must accumulate 4e–/4H+(E4(4H) state) before N2can bind and be reduced. Earlier studies demonstrated that this E4(4H) state stores the reducing-equivalents as two hydrides, with the cofactor metal-ion core formally at its resting-state redox level. This led to the understanding that N2binding is mechanistically coupled to reductive-elimination of the two hydrides that produce H2. The state having acquired 2e–/2H+(E2(2H)) correspondingly contains one hydride with a resting-state core redox level. How the cofactor accommodates addition of the first e–/H+(E1(H) state) is unknown. The Fe-nitrogenase FeFe-cofactor was used to address this question because it is EPR-active in the E1(H) state, unlike the FeMo-cofactor of Mo-nitrogenase, thus allowing characterization by EPR spectroscopy. The freeze-trapped E1(H) state of Fe-nitrogenase shows anS= 1/2 EPR spectrum withg= [1.965, 1.928, 1.779]. This state is photoactive, and under 12 K cryogenicintracavity, 450 nm photolysis converts to a new and likewise photoactiveS= 1/2 state (denoted E1(H)*) withg= [2.009, 1.950, 1.860], which results in a photostationary state, with E1(H)* relaxing to E1(H) at temperatures above 145 K. An H/D kinetic isotope effect of 2.4 accompanies the 12 K E1(H)/E1(H)* photointerconversion. These observations indicate that the addition of the first e–/H+to the FeFe-cofactor of Fe-nitrogenase produces an Fe-bound hydride, not a sulfur-bound proton. As a result, the cluster metal-ion core isformallyone-electron oxidized relative to the resting state. It is proposed that this behavior applies to all three nitrogenase isozymes.