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|Title:||Probing dioxygen activation mechanisms in heme-containing enzymes by heme models|
Cytochrome <i>c</i> oxidase
|Abstract:||In this mini-review, we summarize our recent synthetic model studies on the mechanism of dioxygen reduction reaction involved in cytochrome <i>c </i>oxidase (C<i style="">c</i>O), as well as on the dioxygen binding and activation associated with general heme<b>-</b>containing enzymes. A series of heme/copper dinuclear complexes bearing a cross-linked His-Tyr mimic have been designed and synthesized as synthetic models of the active site of C<i style="">c</i>O, focusing on the possible role(s) of the cross-linked His<b>-</b>Tyr<b>-</b>Cu<sub>B</sub> moiety. The spectroscopic evidences from the oxygenation reaction of these model compounds demonstrate that the role(s) of the cross-linked His<b>-</b>Tyr moiety is more likely to be structural and a proton mediator rather than acting as the fourth electron donor in the dioxygen<i style=""> </i>reduction process<i style="">. </i>It also implies that after one-electron reduction of the oxyheme unit in C<i style="">c</i>O under physiological conditions, O<b>-</b>O bond cleavage could occur through a Fe<sup>III</sup><b>-</b>OOH rather than a peroxo Fe<sup>III</sup><b>-</b>(O<sub>2</sub><sup>2-</sup>)<b>-</b>Cu<sup>II</sup> species. In addition, as key intermediates involved in the catalytic cycles of heme-containing enzymes, the low<b>-</b>spin end-on ferric<b>-</b>peroxo and ferric<b>-</b>hydroperoxo intermediates have been successfully captured and spectroscopically characterized in solution for the first time by using of delicate designed heme models. The results suggest the crucial role of the axial imidazole ligation to heme for O<sub>2</sub> activation|
|Appears in Collections:||IJC-A Vol.50A(03-04) [March-April 2011]|
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