Figure 4.

Distribution of distances between N121 and N139 in different protonation models of CcO. For the other models, see Figure S1. The different models are labelled according to the protonation states of residues D132, E286, K362, and E101, where “0” means unprotonated and “1” means protonated. Letters a–f refer to a ${\mathrm{H}}_3{\mathrm{O}}^{+}$ ion in the K-channel at different heights (see also Table 5 in “Materials and Methods”).