RESUMEN
Energy profiles have been established for the transport of Na+, K+ and Cs+ through the gramicidin A channel. In Urry’s head-to-head β 6.3 left-handed helical dimer structure, using a refined methodology for the calculation of intra and intermolecular interactions. The computations show the important role, for the energy profile and the position of the possible binding site, of the flexible ethanolamine chain, whose significance was till now overlooked. The calculations indicate that the barriers at the entrance and at the center of the channel should be in the order Na+ > K+ > Cs+ but predict also that the energies of the binding sites should be the greatest for Na+ and, then, comparable for K+ and Cs+. The indications concerning the barriers are confirmed by experiment.