Figure 6.

Structural comparison of demonstrated and proposed proton channels towards the BNC in O₂Rs (a–c) and NORs (d,e). D-channel residues are denoted in green, whereas the K-channel and structural analogues thereof are shown in violet. The two hydrophobic and bulky residues interrupting the putative K-channel of cNOR are shown in brown, and the replacement channels transporting protons from the P-side towards the BNC are marked in lighter and darker shades of yellow. Residue numbering is according to the respective pdb-files as indicated in figure 3.