Strong Excitonic Interactions in the Oxygen-Reducing Site of bd-Type Oxidase: The Fe-to-Fe Distance between Hemes d and b595 is 10 Å

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• 作者：Alexander M. Arutyunyan ; Vitaliy B. Borisov ; Vladimir I. Novoderezhkin ; Josh Ghaim ; Jie Zhang ; Robert B. Gennis ; Alexander A. Konstantinov
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：February 12, 2008
• 年：2008
• 卷：47
• 期：6
• 页码：1752 - 1759
• 全文大小：136K
• 年卷期：v.47,no.6(February 12, 2008)
• ISSN：1520-4995

文摘

Absorption and circular dichroism (CD) spectra of cytochrome bd from Escherichia coli havebeen compared for the wild type enzyme and an inactive mutant in which a highly conserved E445 insubunit I has been replaced by alanine [Zhang, J., Hellwig, P., Osborne, J. P., Huang, H. W., Moenne-Loccoz, P., Konstantinov, A. A., and Gennis, R. B. (2001) Biochemistry 40, 8548-8556]. The absorptionbands of ferrous heme b₅₉₅ are absent from the spectrum of the dithionite-reduced E445A form ofcytochrome bd. The difference between the spectra of the dithionite-reduced WT and E445A enzymesindicates that in the mutant, heme b₅₉₅ is present but is not reducible by dithionite. Cytochrome bd revealsintense CD signals dominated by heme d, with almost no contribution from heme b₅₉₅ or heme b₅₅₈. TheCD spectrum of the reduced wild type enzyme in the Soret band indicates strong excitonic interactionsbetween ferrous heme d and ferrous heme b₅₉₅, and these interactions are not observed in dithionite-reduced E445A mutant, in which heme b₅₉₅ remains in the ferric state. Modeling the excitonic interactionsin both absorption and CD spectra has been carried out, yielding an estimate of the Fe-to-Fe distancebetween heme d and heme b₅₉₅ of about 10 Å. The physical proximity supports the hypothesis that hemed and heme b₅₉₅ can form a di-heme oxygen reducing site, a unique structure for respiratory oxidases.