Fourier Transform Infrared Characterization of a CuB-Nitrosyl Complex in Cytochrome ba3 from Thermus thermophilus: Relevance to NO Reductase Activ

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• 作者：Takahiro Hayashi ; I-Jin Lin ; Ying Chen ; James A. Fee ; Pierre Mo&euml ; nne-Loccoz
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：December 5, 2007
• 年：2007
• 卷：129
• 期：48
• 页码：14952 - 14958
• 全文大小：199K
• 年卷期：v.129,no.48(December 5, 2007)
• ISSN：1520-5126

文摘

The two heme-copper terminal oxidases of Thermus thermophilus have been shown to catalyzethe two-electron reduction of nitric oxide (NO) to nitrous oxide (N₂O) [Giuffre, A.; Stubauer, G.; Sarti, P.;Brunori, M.; Zumft, W. G.; Buse, G.; Soulimane, T. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 14718-14723].While it is well-established that NO binds to the reduced heme a₃ to form a low-spin heme {FeNO}⁷ species,the role Cu_B plays in the binding of the second NO remains unclear. Here we present low-temperatureFTIR photolysis experiments carried out on the NO complex formed by addition of NO to fully reducedcytochrome ba₃. Low-temperature UV-vis, EPR, and RR spectroscopies confirm the binding of NO to theheme a₃ and the efficiency of the photolysis at 30 K. The (NO) modes from the light-induced FTIR differencespectra are isolated from other perturbed vibrations using ¹⁵NO and ¹⁵N¹⁸O. The (N-O)a₃ is observed at1622 cm^-1, and upon photolysis, it is replaced by a new (N-O) at 1589 cm^-1 assigned to a Cu_B-nitrosylcomplex. This N-O stretching frequency is more than 100 cm^-1 lower than those reported for Cu-NOmodels with three N-ligands and for Cu_B⁺-NO in bovine aa₃. Because the UV-vis and RR data do notsupport a bridging configuration between Cu_B and heme a₃ for the photolyzed NO, we assign theexceptionally low (NO) to an O-bound (¹-O) or a side-on (²-NO) Cu_B-nitrosyl complex. From this study,we propose that, after binding of a first NO molecule to the heme a₃ of fully reduced Tt ba₃, the formationof an N-bound {CuNO}¹¹ is prevented, and the addition of a second NO produces an O-bond Cu_B-hyponitritespecies bridging Cu_B and Fea₃. In contrast, bovine cytochrome c oxidase is believed to form an N-boundCu_B-NO species; the [{FeNO}⁷{CuNO}¹¹] complex is suggested here to be an inhibitory complex.