Silaghi-Dumitrescu Radu
Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK.
J Inorg Biochem. 2006 Mar;100(3):396-402. doi: 10.1016/j.jinorgbio.2006.01.001. Epub 2006 Feb 10.
Copper-containing nitrite reductases (Cu-NIRs) reduce nitrite to NO. Reported here are DFT (density functional theory) results on models of the Cu-NIR active site bound to nitrite and nitric oxide. The Cu-NIR active site appears to have been designed to exclude N-nitrite binding even though N-O bond cleavage would be equally facile in the N- and O-isomers. The active site also appears to force a side-on coordination of the end-product, nitric oxide. The latter feature has to rely on the sterics of the active site to destabilize, thermodynamically speaking, the Cu-NO adduct; under these conditions, the absence of N-nitrite coordination is proposed to be merely a side-effect. For the Cu(II)-NO adduct, sterical crowding appears to also favour the Cu-NO electromer over Cu(I)-NO+, helping to avoid the potentially damaging chemistry associated with an NO+ moiety. These conclusions are in reasonable agreement with previous conclusions drawn from experiment [Science 304 (2004) 867].
含铜亚硝酸还原酶（Cu-NIRs）将亚硝酸盐还原为一氧化氮。本文报道了关于与亚硝酸盐和一氧化氮结合的Cu-NIR活性位点模型的密度泛函理论（DFT）结果。尽管在N-异构体和O-异构体中N-O键断裂同样容易，但Cu-NIR活性位点似乎被设计成排除N-亚硝酸盐结合。活性位点似乎还迫使终产物一氧化氮以侧基配位方式结合。从热力学角度讲，后一个特征必须依靠活性位点的空间效应来使Cu-NO加合物不稳定；在这些条件下，N-亚硝酸盐不发生配位被认为仅仅是一种副作用。对于Cu(II)-NO加合物，空间拥挤似乎也有利于形成Cu-NO电异构体而非Cu(I)-NO⁺，这有助于避免与NO⁺部分相关的潜在有害化学反应。这些结论与先前从实验得出的结论[《科学》304 (2004) 867]合理地一致。
