Referenced in: none

Automatically associated channels: Kv2.1 , Slo1

Title: Tryptophan contributions to the empirical free-energy profile in gramicidin A/M heterodimer channels.

Authors: Jacob Devin Durrant, Devin Caywood, David D Busath

Journal, date & volume: Biophys. J., 2006 Nov 1 , 91, 3230-41

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/16861266

Abstract
Gramicidin A/gramicidin M heterodimer conductances were measured in planar lipid bilayers and found to form two distinguishable populations about halfway between the gramicidin A and gramicidin M homodimer conductances. This implies that the principle difference in the gramicidin A and gramicidin M transport free-energy profiles occurs at the channel center, where it would produce similar effects on the rate-limiting barrier for the two heterodimers. Kinetic analysis based on this and nearly all previously published homodimer conductance data for both gramicidin A and gramicidin M channels confirms this conclusion, indicating that the translocation step is approximately 100-fold slower in gramicidin M homodimers than in gramicidin A homodimers and that first- and second-ion exit-rate constants are higher by factors of 24 and 10, respectively. Assuming that the ratios of rate constants are related to the free-energy difference between gramicidin A and gramicidin M, we construct an effective ion-Trp free-energy interaction profile that has a minimum at the channel center.