Species heterogeneity of Gly-11 gramicidin A incorporated into sodium dodecyl sulfate micelles.

Evidence is presented for species heterogeneity of the gly-11 analog of gramicidin A incorporated into sodium dodecyl sulfate (SDS) micelles. The evidence for species heterogeneity has been obtained using one-dimensional (1D) 1H NMR spectroscopy. The 1D spectra of the indole NH moiety of tryptophans 9, 13, and 15 show the presence of more than one species. It has been found that the heterogeneity is dependent upon the gly-11/SDS molar ratio. At high SDS concentration (i.e., gly-11/SDS of 3 mM/700 mM) the heterogeneity almost completely disappears. The temperature dependence of these 1H NMR signals suggests that the two species do not interconvert. The results of nuclear Overhauser effect spectroscopy NMR experiments indicate that one species is embedded within the micelle, while the other is nearer the aqueous interface. The importance of side chain interactions with the membrane environment in producing stable, solubilized species of small peptides in SDS micelles is illustrated.