Figure 6. Subunit symmetry of αV218 mutants.

Left, 2 hybrid populations were apparent in αV218Y. The change in gating energy for the double mutant (Dbl) was equal to the sum of these energies calculated for the individual hybrid populations (H1 and H2). Right, one hybrid population was apparent in αV218F. The gating energy change for the double-mutant was exactly twice that of the hybrid. The αV218F mutation is energetically symmetric in the two α subunits, so that the two hybrids appear as a single population. For both F and Y substitutions, the φ values for the hybrids were the same as for the double mutant.