Dioxygen activation and bond cleavage by mixed-valence cytochrome c oxidase
Dioxygen activation and bond cleavage by mixed-valence cytochrome c oxidase
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DOI：
10.1073/pnas.95.14.8020
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发表时间：
1998-07-07
影响因子：
11.1
通讯作者：
Babcock, GT
中科院分区：
文献类型：
--
作者：
Proshlyakov, DA;Pressler, MA;Babcock, GT
阐明细胞色素 c 氧化酶将 O-2 还原为水的中间体结构对于理解酶的氧活化和质子泵送至关重要。在这项工作中，O-2 与混合价酶的反应，其中只有双核中心的血红素 a(3) 和 Cu-B 被还原，并通过时间分辨共振拉曼光谱进行跟踪。结果表明，O=O键断裂发生在反应引发后200μs内；未检测到独特稳定的 Fe-O-O(H) 过氧物质的存在。这种快速反应的产物是血红素 a(3) 氧铁基 (Fe-IV=O) 物质，这要求除了血红素 a(3) 和 Cue 之外还必须有电子供体参与。现有证据表明额外的供体是氨基酸侧链。最近的晶体学数据 [Yoshikawa, S,, Shinzawa-Itoh, K,, Nakashima, R, Yaono, R,, Yamashita, E,, Inoue, N,, Yao, M,, Fel, M, J,, Libeu, C, P,, Mizushima, T,, et nl。科学，正在出版； Ostermeier, C,、Harrenga, A、Ermler, U 和 Michel, H, (1997) Proc。国家。阿卡德。科学。 USA 94, 10547-10553]表明 Cu-B 配体之一 His240 与 Tyr244 交联，并且该交联的酪氨酰处于参与双氧活化的理想位置。我们提出了一种 O-O 键断裂机制，该机制通过从交联的 His-Tyr 物种中协调氢原子转移来产生产物氧代铁基物种、Cu-B(2+)-OH- 和酪氨酰自由基。该机制提供了驱动氧化酶中质子泵的两个关键中间体的分子结构；此外，它与光合作用中 O-2 演化过程中发生的 O-O 键形成化学有明显的相似之处。
Elucidating the structures of intermediates in the reduction of O-2 to water by cytochrome c oxidase is crucial to understanding both oxygen activation and proton pumping by the enzyme. In the work here, the reaction of O-2 with the mixed-valence enzyme, in which only heme a(3) and Cu-B in the binuclear center are reduced, has been followed by time-resolved resonance Raman spectroscopy. The results show that O=O bond cleavage occurs within the first 200 mu s after reaction initiation; the presence of a uniquely stable Fe-O-O(H) peroxy species is not detected. The product of this rapid reaction is a heme a(3) oxoferryl (Fe-IV=O) species, which requires that an electron donor in addition to heme a(3) and Cue must be involved. The available evidence suggests that the additional donor is an amino acid side chain. Recent crystallographic data [Yoshikawa, S,, Shinzawa-Itoh, K,, Nakashima, R, Yaono, R,, Yamashita, E,, Inoue, N,, Yao, M,, Fel, M, J,, Libeu, C, P,, Mizushima, T,, et nl. Science, in press; Ostermeier, C,, Harrenga, A, Ermler, U, & Michel, H, (1997) Proc. Natl. Acad. Sci. USA 94, 10547-10553] show that one of the Cu-B ligands, His240, is cross-linked to Tyr244 and that this cross-linked tyrosyl is ideally positioned to participate in dioxygen activation. We propose a mechanism for O-O bond cleavage that proceeds by concerted hydrogen atom transfer from the cross-linked His-Tyr species to produce the product oxoferryl species, Cu-B(2+)-OH-, and the tyrosyl radical. This mechanism provides molecular structures for two key intermediates that drive the proton pump in oxidase; moreover, it has clear analogies to the proposed O-O bond forming chemistry that occurs during O-2 evolution in photosynthesis.