Mechanism of H-H activation by nickel-iron hydrogenase
Mechanism of H-H activation by nickel-iron hydrogenase
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DOI：
10.1021/ja971681
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发表时间：
1998-01-28
影响因子：
15
通讯作者：
Crabtree, RH
中科院分区：
文献类型：
--
作者：
Pavlov, M;Siegbahn, PEM;Crabtree, RH
用密度泛函量子化学方法研究了镍-铁氢化酶的反应机理。从实验的X-射线结构，所有合理的氧化态和自旋态进行了研究，NiFe簇的结构和反应模式是最好的再现通过假设NiFe（II，III）的氧化态分配的集群的静止状态。在我们提出的酶氧化H-2的机制中，H-2首先以分子氢络合物的形式与Fe结合，然后进行异裂。这个过程是自旋相关的，不会发生在高自旋六重态。在关键步骤中，氢化物转移到铁和质子转移到相邻的半胱氨酸硫醇配体伴随着从Ni的质子化半胱氨酸硫醇的解配位，同时保持与铁结合。同时，铁上的氰化物配体以罕见的桥接结合模式与镍原子结合。在H-2解离之后，与Fe结合的氢化物然后可以转移到Ni，这应该是随后的氢原子或电子传输的必要预备。对氢裂解的过渡态进行了定位，计算的能垒与实验值吻合得很好。
DFT quantum chemical methods are used to probe the mechanism of the nickel-iron hydrogenases. Starting from the experimental X-ray structure, all plausible oxidation states and spin states were investigated, The structure and reactivity pattern of the NiFe cluster are best reproduced by assuming a NiFe(II,III) oxidation state assignment of the resting state of the cluster. In our proposed mechanism of H-2 oxidation by the enzyme, H-2 first binds to Fe in the form of a molecular hydrogen complex, which then undergoes heterolytic splitting. This process is spin-dependent and does not occur for the high-spin sextet state. In the key step, hydride transfer to iron and proton transfer to the adjacent cysteinethiolate ligand is accompanied by decoordination of the protonated cysteinethiol from Ni while remaining bound to iron. Simultaneously, the cyanide ligand on iron binds with the nickel atom in a rare bridging binding mode. After the H-2 dissociation, the hydride bound to Fe can then be transferred to Ni which should be a necessary preliminary for subsequent hydrogen atom or electron transport. The transition state for hydrogen splitting was located, and the resulting calculated energy barrier is in remarkably good agreement with the experimental value.