Figure 29.

Mechanism of O₂ reduction to water by the MCOs. Red arrows indicate the steps that take place in catalytic cycle of the MCOs. Black arrows indicate steps that can be experimentally observed but are not part of the catalytic cycle. The dashed arrows at the right indicate the transfer of an electron from the T1 Cu to the T2 Cu to create PI+e⁻, that occurs in going from PI to NI but is not experimentally observed in the wild type enzyme.