The gramicidin A channel: comparison of the energy profiles of Na+, K+ and Cs+. Influence of the flexibility of the ethanolamine end chain on the profiles.

The energy profiles for single occupancy by Cs+, K+ and Na+ in the gramicidin A channel assumed to be in a head-to-head beta 6.3 3.3 helical dimeric structure, were computed: (A) allowing complete conformational freedom to the ethanolamine end, (B) constraining it to stay in its intrinsically preferred conformation. Whatever the constraint, both the entrance barrier and the central barrier appear in the order Cs+ less than K+ less than Na+. Introducing the flexibility of the tail modifies appreciably the profiles and the location of the extrema along it.