The Nature of the Exchange Coupling between High-Spin Fe(III) Heme o3 and CuB(II) in Escherichia coli Quinol Oxidase, Cytochrome bo
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- 作者：Myles R. Cheesman ; Vasily S. Oganesyan ; Nicholas J. Watmough ; Clive S. Butler ; and Andrew J. Thomson
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：April 7, 2004
- 年：2004
- 卷：126
- 期：13
- 页码：4157 - 4166
- 全文大小：197K
- 年卷期：v.126,no.13(April 7, 2004)
- ISSN：1520-5126
文摘
Fully oxidized cytochrome bo3 from Escherichia coli has been studied in its oxidized and severalligand-bound forms using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD)spectroscopies. In each form, the spin-coupled high-spin Fe(III) heme o3 and CuB(II) ion at the active sitegive rise to similar fast-relaxing broad features in the dual-mode X-band EPR spectra. Simulations of dual-mode spectra are presented which show that this EPR can arise only from a dinuclear site in which themetal ions are weakly coupled by an anisotropic exchange interaction of 
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1 cm-1. A variable-temperatureand magnetic field (VTVF) MCD study is also presented for the cytochrome bo3 fluoride and azide derivatives.New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presenceof strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPRstudy, also shows that the spin-coupling within the active site is weak with rbar.gif">Jrbar.gif"> 1 cm-1. These conclusionsoverturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an S' = 2ground state resulting from strong exchange coupling (rbar.gif">Jrbar.gif"> > 102 cm-1) within the active site.
rbar.gif">Jrbar.gif"> 1 cm-1. A variable-temperatureand magnetic field (VTVF) MCD study is also presented for the cytochrome bo3 fluoride and azide derivatives.New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presenceof strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPRstudy, also shows that the spin-coupling within the active site is weak with rbar.gif">Jrbar.gif"> 1 cm-1. These conclusionsoverturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an S' = 2ground state resulting from strong exchange coupling (rbar.gif">Jrbar.gif"> > 102 cm-1) within the active site.