Computational Study of the Non-Heme Iron Active Site in Superoxide Reductase and Its Reaction with Superoxide
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- 作者：Radu Silaghi-Dumitrescu ; Ioan Silaghi-Dumitrescu ; Eric D. Coulter ; and Donald M. Kurtz ; Jr.
- 刊名：Inorganic Chemistry
- 出版年：2003
- 出版时间：January 27, 2003
- 年：2003
- 卷：42
- 期：2
- 页码：446 - 456
- 全文大小：231K
- 年卷期：v.42,no.2(January 27, 2003)
- ISSN：1520-510X
文摘
The ferrous square-pyramidal [Fe(NHis)4(SCys)] site of superoxide reductases (SORs) has been shown to reducesuperoxide at a nearly diffusion-controlled rate. The final products of the reaction are hydrogen peroxide and theferric hexacoordinated SOR site, with a carboxylate group from a conserved glutamate serving as the sixth ligandtrans to the cysteine sulfur. A transient intermediate absorbing at ~600 nm in the reaction of the ferrouspentacoordinated site with superoxide has been proposed to be a ferric-(hydro)peroxo complex (Coulter, E.; Emerson,J.; Kurtz, D. M., Jr.; Cabelli, D. J. Am. Chem. Soc. 2000, 122, 11555-11556.). In the present study, DFT andZINDO/S-CI results are shown to support the description of the 600-nm intermediate as an end-on, low-spin ferric-peroxo or -hydroperoxo complex. Side-on peroxo coordination was found to be significantly less stable than end-on because of constraints on the imidazole ligand ring orientations imposed mostly by the protein. The modeledferric-hydroperoxo complex had a decidedly nonplanar CysC
-S-Fe-O-O geometry that appears to be imposedby the same constraints. A single prominent visible absorption of the (hydro)peroxo model is shown to be duemainly to a CysS 
Fe(III) 
charge transfer (CT) transition with a minor portion of His Fe(III) CT characterand very little peroxo Fe(III) CT character. On the basis of calculations of models with various mono- anddiprotonated peroxo ligands, protonation of the iron-bound peroxo oxygen is a key step in the decay of the ferric-(hydro)peroxo complex favoring release of hydrogen peroxide over cleavage of the O-O bond, as occurs in theheme structural analogue, cytochrome P450.
-S-Fe-O-O geometry that appears to be imposedby the same constraints. A single prominent visible absorption of the (hydro)peroxo model is shown to be duemainly to a CysS Fe(III) charge transfer (CT) transition with a minor portion of His Fe(III) CT characterand very little peroxo Fe(III) CT character. On the basis of calculations of models with various mono- anddiprotonated peroxo ligands, protonation of the iron-bound peroxo oxygen is a key step in the decay of the ferric-(hydro)peroxo complex favoring release of hydrogen peroxide over cleavage of the O-O bond, as occurs in theheme structural analogue, cytochrome P450.