Can Reduction of NO to N2O in Cytochrome c Dependent Nitric Oxide Reductase Proceed through a Trans-Mechanism?
Can Reduction of NO to N2O in Cytochrome c Dependent Nitric Oxide Reductase Proceed through a Trans-Mechanism?
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DOI：
10.1021/acs.biochem.6b00788
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发表时间：
2017-01-10
期刊：
影响因子：
2.9
通讯作者：
Blomberg, Margareta R. A.
中科院分区：
文献类型：
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作者：
Blomberg, Margareta R. A.
作为微生物反硝化作用的一部分，NO在膜结合酶一氧化氮还原酶（NOR）中被还原为N2O， N - N偶联发生在二铁双核活性位点（BNC），这一反应步骤的不同机制已被提出。计算研究支持所谓的顺式：b(3)-机制，其中还原性N - N键形成的次亚硝酸盐产物与BNC中的一个氮与血红素铁结合，两个氧与非血红素铁结合。相反，实验结果被解释为支持所谓的反式机制，其中亚硝酸盐中间体与两个铁离子中的每个氮原子配位。混合密度泛函理论在这里被用来执行一个广泛的搜索可能的中间体在cNOR酶的NO还原。发现带负电的氧与带正电的铁离子配位的亚硝酸盐结构是最稳定的结构。在建议的反式机制中涉及的次亚硝酸盐中间体，只与氮离子配合铁离子，被发现能量过高，导致反应太慢，这应该排除这种机制。此外，在BNC中，将一个NO分子与每个铁离子结合的中间体被认为启动了反式机制，但发现能量太高而无法观察到，这表明实验观察到的支持这种铁-亚硝基二聚体中间体的电子顺磁共振信号应该重新解释。
As part of microbial denitrification, NO is reduced to N2O in the membrane bound enzyme nitric oxide reductase, NOR The N N coupling occurs in the diiron binuclear active site, BNC, and different mechanisms for this reaction step have been suggested. Computational studies have supported a so-called cis:b(3)-mechanism, in which the hyponitrite product of the reductive N N bond formation coordinates with one nitrogen to the heme iron and with both oxygens to the non-heme iron in the BNC. In contrast, experimental results have been interpreted to support a so-called trans-mechanism, in which the hyponitrite intermediate coordinates with one nitrogen atom to each of the two iron ions. Hybrid density functional theory is used here to perform an extensive search for possible intermediates of the NO reduction in the cNOR enzyme. It is found that hyponitrite structures coordinating with their negatively charged oxygens to the positively charged iron ions are the most stable ones. The hyponitrite intermediate involved in the suggested trans-mechanism, which only coordinates with the nitrogens to the iron ions, is found to be prohibitively high in energy, leading to a too slow reaction, which should rule out this mechanism. Furthermore, intermediates binding one NO molecule to each iron ion in the BNC, which have been suggested to initiate the trans-mechanism, are found to be too high in energy to be observable, indicating that the experimentally observed electron paramagnetic resonance signals, taken to support such an iron-nitrosyl dimer intermediate, should be reinterpreted.