Fig. 3.

Conformational exchange for dimeric gramicidin A in isotropic solvents is enhanced by more than a 1000 fold by the addition of water (a protic solvent) that can facilitate hydrogen bond exchange. The conformational exchange is observed by GCOSY spectra of various double helical gramicidin A conformations in dioxane (a non-protic solvent). The red resonances highlight the stable state in this environment and its corresponding conformation is highlighted in red. a-c). a, d-f) In the presence of approximately 1% water in dioxane the conversion occurs in less than 1 h. This suggests that conformational interconversion in native membranes may be hindered by the sparsity of water in the membrane interstices. Reproduced with permission from (Xu and Cross 1999).