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It has been suggested that the alanine-based peptide with sequence Ac-XX-[A]₇-OO-NH₂, termed XAO where X denotes diaminobutyric acid and O denotes ornithine, exists in a predominantly polyproline-helix (P_II) conformation in aqueous solution. In our recent work, we demonstrated that this "polyproline conformation" should be regarded as a set of local conformational states rather than as the overall conformation of the molecule. In this work, we present further evidence to support this statement. Differential scanning calorimetry measurements showed only a very small peak in the heat capacity of an aqueous solution of XAO at 57°C, whereas the suggested transition to the P_II structure should occur at ∼30°C. We also demonstrate that the temperature dependence of the ³J_HNHα coupling constants of the alanine residues can be explained qualitatively in terms of Boltzmann averaging over all local …