O₂ Reduction to H₂O by the multicopper oxidases

In nature the four electron reduction of O₂ to H₂O is carried out by Cytochrome c oxidase (CcO) and the multicopper oxidases (MCOs). In the former, Cytochrome c provides electrons for pumping protons to produce a gradient for ATP synthesis, while in the MCOs the function is the oxidation of substrates, either organic or metal ions. In the MCOs the reduction of O₂ is carried out at a trinuclear Cu cluster (TNC). Oxygen intermediates have been trapped which exhibit unique spectroscopic features that reflect novel geometric and electronic structures. These intermediates have both intact and cleaved O–O bonds, allowing the reductive cleavage of the O–O bond to be studied in detail both experimentally and computationally. These studies show that the topology of the TNC provides a unique geometric and electronic structure particularly suited to carry out this key reaction in nature.