Fig. 7. Observed changes in the selectivity (reversal potential) in yeast VDAC channels following single site-directed mutations. The reversal potentials were divided by the magnitude and sign of the charge change at the site produced by the amino-acid substitution. They are plotted against the position of the residue from the N terminus. The reversal potentials are compilations of previously-published data (Blachly-Dyson et al, 1990; Peng et al., 1992a). The were collected on single channels after reconstitution into a planar membrane (as in Fig. 1) in the presence of a 10 fold KCl gradient. Positive values indicate that the selectivity change was in the direction expected from the charge change. Solid bars represent significant changes in selectivity.