Figure 4.

Structural model of the redox centers in A. ambivalens aa₃ oxidase. The model was created based on the structural coordinates of Paracoccus cytochrome c oxidase, taking only the first 491 residues of the amino acid sequence into consideration. The residues are numbered as in bovine sequence. Shown in the picture are heme a, heme a₃ (red), Cu_B (blue), and some of the neighboring residues (in thick lines), His-290 (one of the three histidine ligands to Cu_B), Tyr-244, Asp-364, His-368, Arg-438, and Arg-439. The residues shown in thin lines but not labeled are the histidine ligands to hemes a and a₃ and Cu_B. The arrows denote the proposed path of proton translocation from His-290 to the Asp-364–propionate pair to the Arg-438–propionate region.