Spectroscopic elucidation of a new heme/copper dioxygen structure type: implications for O···O bond rupture in cytochrome c oxidase.
Spectroscopic elucidation of a new heme/copper dioxygen structure type: implications for O···O bond rupture in cytochrome c oxidase.
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DOI：
10.1002/anie.201104080
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发表时间：
2012-01-02
影响因子：
16.6
通讯作者：
Solomon, Edward I.
中科院分区：
文献类型：
--
作者：
Kieber-Emmons, Matthew T.;Qayyum, Munzarin F.;Li, Yuqi;Halime, Zakaria;Hodgson, Keith O.;Hedman, Britt;Karlin, Kenneth D.;Solomon, Edward I.
Cytochromec oxidase (CcO) catalyzes the four-electron reduction of dioxygen to form water in the terminal step of the electron transport chain.[1] Dioxygen binds to a unique heme–copper bimetallic active site, wherein the copper is ligated about 5 above the heme by three His residues.[2, 3] One of these ligating His residues is covalently crosslinked to a nearby Tyr residue. The crosslinked Tyr is thought to participate in catalysis by providing the fourth electron needed to cleave the OÀO bond in a net hydrogen abstraction.[4] This hypothesis stems from the observation of an intermediate state (PM) in CcO that occurs after OÀO bond cleavage, which is suggested to contain a tyrosyl radical based on chemical and spectral evidence.[5–8] The only observable enzymatic dioxygen intermediate before OÀO bond rupture has been assigned as a ferric–superoxo species (A),[9, 10] leading some to suggest this species is directly responsible for the net hydrogen abstraction from Tyr.[11, 12] We and others favor an alternative mechanistic scenario in which an unobserved peroxo intermediate functions as the active oxidant.[13–15] A putative peroxo moiety would take advantage of the His–Tyr crosslink and the copper ion as a pathway to access the fourth electron necessary for cleavage of its OÀO bond. However, heme–peroxo–copper adducts are generally unreactive towards phenols, thus motivating efforts towards understanding factors required for OÀO bond rupture by heme–copper sites. Recently, we reported preliminary evidence that the reaction of a heme–peroxo–copper adduct {[F8Fe]-O2-[CuAN]}+(1; F8= 5, 10, 15, 20-tetrakis (2, 6-difluorophenyl) porphyrinate, AN= bis (3-(dimethylamino) propyl)-amine) with a coordinating base DCHIm (DCHIm= 1, 5-dicyclohexylimidazole) results in formation of a discrete complex (2) that has enhanced reactivity towards phenols.[16] Herein we present the molecular and electronic structure of 2, which is an example of a heme–peroxo–copper complex in which the electronic state of the heme fragment is low-spin (LS).[17] Concomitant with the change in spin of the heme fragment from high-spin (HS) to LS upon conversion from 1 to 2, the Fe-O2-Cu core undergoes a change from μ-η2: η2 (side-on) in 1 to μ-1, 2 (end-on) in 2 (Scheme 1). This novel bridging mode has not been observed previously in heme–copper model complexes, but it has been proposed in recent crystallographic studies on resting CcO.[18–20] However, comparison of the spectral features of resting CcO to those described herein for 2 reveal inconsistencies, suggesting a reevaluation of the bridging mode of the peroxo group in resting CcO and providing insight into the electronic structure requirements for OÀO bond cleavage. Low-temperature reaction of a degassed THF solution of 1 with a molar equivalent of DCHIm generated 2, as indicated by changes in the optical spectrum (Figure 1). Specifically, a shift in the Soret band from 418 nm (e= 133.6 L mmolÀ1 cmÀ1) to 421 nm (e= 142.7 L mmolÀ1 cmÀ1) was observed along with a shift and collapse of the split Qband of 1 (lmax [nm](e [L mmolÀ1 cmÀ1])= 538 (8.4), 561 (6.9)) to 537nm (e= 11.5 L mmolÀ1 cmÀ1) in 2. While the spectrum of 2 is dominated by the heme spectral features, two low-energy features were observed at 789 nm (e= 1.5 L mmolÀ1 cmÀ1) and 951 nm
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影响因子：
64.8
作者：
IWATA, S;OSTERMEIER, C;MICHEL, H
通讯作者：
MICHEL, H
影响因子：
56.9
作者：
Collman, James P.;Devaraj, Neal K.;Chidsey, Christopher E. D.
通讯作者：
Chidsey, Christopher E. D.
影响因子：
3
作者：
Oganesyan, Vasily S.;White, Gaye F.;Thomson, Andrew J.
通讯作者：
Thomson, Andrew J.
影响因子：
4.9
作者：
Collman, James P.;Decreau, Richard A.;Sunderland, Christopher J.
通讯作者：
Sunderland, Christopher J.
影响因子：
4.6
作者：
Halime, Zakaria;Kieber-Emmons, Matthew T.;Qayyum, Munzarin F.;Mondal, Biplab;Gandhi, Thirumanavelan;Puiu, Simona C.;Chufan, Eduardo E.;Sarjeant, Amy A. N.;Hodgson, Keith O.;Hedman, Britt;Solomon, Edward I.;Karlin, Kenneth D.
通讯作者：
Karlin, Kenneth D.