Structure of alamethicin in solution: nuclear magnetic resonance relaxation studies

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Abstract
A NMR relaxation study at 500 MHz of the icosapeptide antibiotic alamethicin is reported. A partly helical, partly extended, amphiphilic and dimeric structure was suggested. The N-acetyl methyl groups toward the N terminus of alamethicin in this solvent system exhibited unusual NMR relaxation behavior. The decay of the transverse magnetization due to these protons was nonexponential; the spin-lattice relaxation recovery of the longitudinal magnetization was exponential. In a solution saturated with urea, both decays were exponential. These observations were consistent with the proposed structure. Studies in H2O yielded qualitatively similar, but more complex results. The transverse relaxation times suggest further aggregation in H2O and indicate that the larger aggregates in H2O may be made up of the smaller units observed in methanol.

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