Evidence to Support the Model

In the binuclear haem-copper centre of cytochrome oxidases there is no cation radical formed at the active site. Instead the extra positive charge is held by the copper atom as it converts from cuprous (Cu1+) to cupric (Cu2+). In fact there is growing evidence to support the model of Mitchell [56] that it is the protonation steps associated with oxidation state changes in this copper atom (Cub) that provide the link between the electron transfer and proton translocation activities of this enzyme. 

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