2d Nmr of Single and Double Stranded Helices of Gramicidin a in Micelles and Solutions

The linear pentadecapeptide gramicidin A (GA) HCO-L-Val-Gly-L-Ala-Z)Leu4-L-Ala-£»-Val-L-Val-Z?-Val-LTrp-Z^Leu-L-Trp-Z>-Leu-L-TrpD-Leu-L-Trp-NHCH2CH2OH attracts attention due to its ability to form monovalent cations permeable channels in membranes. Once it has been appreciated (1), that two molecules of GA are combined in such a way as to span the membrane bilayer (Fig. 1) a number of detailed models of the channel were proposed. The models were based on obvious requirements of such a structure: (i) a lipophilic exterior and hydrophilic axial cavity; (ii) a length sufficient to span the lipid portion of the bilayer; and (iii) the capacity to interact with ions. The problem of spatial structure of the GA channel is dramatically complicated because of diver-