Dioxygen Binding, Proton Translocation, and Electron Transport

3 Dioxygen Binding, Proton Translocation, and Electron Transport 

In the fully reduced model, four electrons are transferred to dioxygen through sequential one-electron oxidations of heme as s iron ion, the Cub ion, the heme a iron ion, and one of the bimetallic center s Cua ions. The sequence of electron transferal differs in the mixed valence model, and a tyrosine radical (tyr) is generated. The proposed formation of a tyrosine radical during catalytic turnover arises from the known post-translational modification in most CcO s in which a covalent bond is formed between the his240 ligand of Cub 

0-0 bond cleavage formation oxo-ferryl state at heme a. internal pT at catalytic site (H transfer from YOH to Cub(I) and formation of tyrosine radical) 

PDB 1M56 R. spharoides D and K pathway entrance aa residues in green. H-bonding network aa residues in blue. Red dashed lines describe proton translocation routes. 

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