The effects of bilayer thickness and tension on gramicidin single-channel lifetime.

Measurements have been made of gramicidin single-channel lifetimes in monoacylglycerol bilayers chosen so that their thickness ranged from above to below the length of the gramicidin channel. Contact angles, electrical capacities and bulk-phase interfacial tensions have also been determined for these systems. The mean channel lifetime decreased with the hydrocarbon thickness of the membrane until the latter reached 2.2 nm, after which the lifetime was relatively constant. A theoretical model has been proposed which relates the mean channel lifetime (or dissociation constant) to both the thickness and the tension of the bilayers. The analysis of the present results and of those of previous studies has led to the idea that aggregates of water molecules may play an important rôle in the dissociation of the gramicidin channel.