Figure 5. Free energy barriers experienced by O₂.

Free energy barriers experienced by O₂ when moving from the membrane region to the BNC, along Channel 1 (A), Channel 2 (B) and Channel 3 (C). For details related to the errors calculation see the data analysis section of the Materials and Methods. The “*” in the fig. indicates the transitions for which the errors could not be calculated. In Fig. A, the black lines correspond to Channel 1, which starts between helices 5 and 8 of subunit I, whereas the orange lines correspond to the second entrance point located between helices 11 and 13 of subunit I. In A and C, the dashed lines correspond to alternative routes for O₂ inside the same channel (for example in Fig. C, O₂ can move directly from M₁₄ to M₁₆, or it can go from M₁₄ to M₁₅ and only then to M₁₆). The numbers inside the plots on top of the transition states indicate the free energy barriers experienced by O₂ when moving from the membrane in the direction of the BNC (i.e. between the different minima on their immediate left and the transition states in question).