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Bovine cytochrome c oxidase structures enable O 2 reduction with minimization of reactive oxygens and provide a proton-pumping gate

2010; National Academy of Sciences; Volume: 107; Issue: 17 Linguagem: Inglês

10.1073/pnas.0910410107

1091-6490

Kazumasa Muramoto, Kazuhiro Ohta, Kyoko Shinzawa‐Itoh, K. Kanda, Maki Taniguchi, Hiroyuki Nabekura, Eiki Yamashita, Tomitake Tsukihara, Shinya Yoshikawa,

Electrochemical Analysis and Applications

The O 2 reduction site of cytochrome c oxidase (CcO), comprising iron (Fe a 3 ) and copper (Cu B ) ions, is probed by x-ray structural analyses of CO, NO, and CN - derivatives to investigate the mechanism of the complete reduction of O 2 . Formation of the derivative contributes to the trigonal planar coordination of and displaces one of its three coordinated imidazole groups while a water molecule becomes hydrogen bonded to both the CN - ligand and the hydroxyl group of Tyr244. When O 2 is bound to , it is negatively polarized ( ), and expected to induce the same structural change induced by CN - . This structural change allows to receive three electron equivalents nonsequentially from , , and Tyr-OH, providing complete reduction of O 2 with minimization of production of active oxygen species. The proton-pumping pathway of bovine CcO comprises a hydrogen-bond network and a water channel which extend to the positive and negative side surfaces, respectively. Protons transferred through the water channel are pumped through the hydrogen-bond network electrostatically with positive charge created at the Fe a center by electron donation to the O 2 reduction site. Binding of CO or NO to induces significant narrowing of a section of the water channel near the hydrogen-bond network junction, which prevents access of water molecules to the network. In a similar manner, O 2 binding to is expected to prevent access of water molecules to the hydrogen-bond network. This blocks proton back-leak from the network and provides an efficient gate for proton-pumping.