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Lookup NU author(s): Dr Clive Butler
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Fully oxidized cytochrome bo3 from Escherichia coli has been studied in its oxidized and several ligand-bound forms using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopies. In each form, the spin-coupled high-spin Fe(III) heme o 3 and CuB(II) ion at the active site give 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 the metal ions are weakly coupled by an anisotropic exchange interaction of |J| ā 1 cm-1. A variable-temperature and magnetic field (VTVF) MCD study is also presented for the cytochrome bo 3 fluoride and azide derivatives. New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presence of strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPR study, also shows that the spin-coupling within the active site is weak with |J| ā 1 cm-1. These conclusions overturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an Sā² S = 2 ground state resulting from strong exchange coupling (|J| > 102 cm-1) within the active site.
Author(s): Cheesman MR, Oganesyan VS, Watmough NJ, Butler CS, Thomson AJ
Publication type: Article
Publication status: Published
Journal: Journal of the American Chemical Society
Year: 2004
Volume: 126
Issue: 13
Pages: 4157-4166
ISSN (print): 0002-7863
ISSN (electronic): 1943-2984
Publisher: American Chemical Society
URL: http://dx.doi.org/10.1021/ja038858m
DOI: 10.1021/ja038858m
PubMed id: 15053605
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