Fig. 6.

Computed free energy of H⁺/Na⁺ selectivity of the c subunit binding sites in M. acetivorans, relative to that of the I. tartaricus c₁₁ ring. More negative values indicate greater selectivity for H⁺ and against Na⁺. All values are given in reference to analogous calculations for the complete c₁₁ ring from I. tartaricus, previously reported (32). Selectivity values are shown for two alternative models of a M. acetivorans c₄ oligomer, one based on the architecture of the I. tartaricus c₁₁ ring (Left), and another based on the c₁₅ ring from S. platensis (Right). The computed selectivity of analogous c₄ constructs from I. tartaricus, S. platensis, and B. pseudofirmus OF4 is also given.