The single-channel conductance lambda and the mean channel lifetime gamma of natural and synthetic gramicidins A, B, and C has been studied. Significant differences in delta were found between gramicidin A and B; both gramicidins differ only in one amino acid (tryptophan replaced by phenylaline). The distribution of lambda is narrow in glycerylmonooleate membranes but considerably broader in dioleoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine membranes. The ratio of the single-channel conductances in glycerylmonooleate and dioleoyl phosphatidylcholine membranes is only about two and is considerable smaller than the conductance ratio of nonactin-mediated cation transport. This finding suggests that dipolar potentials at the membrane/solution interface have little influence on the conductance of the gramicidin channel.
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