Dispersity of des-L X Val7-D X Val8-Gramicidin A single channel conductances argues for different side chain orientations as basis.

Planar bilayer studies are reported on the channel activity of des-L X Val7-D X Val8-Gramicidin A. This analog is designed to provide more long-lived side chain distributions involving the Trp residues than occur with Gramicidin A. The carbonyls of these residues coordinate the permeant cation and the energetics of the coordination, which is proposed to depend on side chain orientation, determines the free energies of the rate limiting entrance-exit barriers and the binding sites. The finding of an increased dispersity of single channel conductance for the analog supports the perspective that dispersity derives from different side chain distributions on the same backbone conformation. Channel mechanism is not understood until dispersity is explained.