Fig. 5. Stereo representation of the electron transfer pathways in the ba₃-cytochrome c oxidase from T.thermophilus. The haems b and a_s3 are shown in orange, the copper atoms in blue and the metal-ligating amino acid residues in green. The two arginine residues (Arg450 and Arg449) and Phe385, which are involved in the electron transfer from Cu_A via haem b to the active site haem a_s3 Cu_B are depicted in purple. The residues that form the newly postulated electron transfer pathway leading from Cu_A to the aromatic ring system of Tyr136 and from there via a hydrogen bond and Trp229 to the Cu_B ligand His238 are represented in cyan, including the corresponding distances. This figure was prepared with MAIN (Turk, 1992).