Abstract
ABSTRACTShort alanine (Ala) oligopeptides in aqueous solution adopt polyproline II [PPII; (φ, ψ) = (−60°, 150°)] and extended β conformations [(φ, ψ) = (−150°, 150°)], whose conformers are related to the denatured state of proteins. In this study, we investigated pressure-induced conformational changes of penta- and hexa-alanines (Ala5 and Ala6, respectively) in aqueous solutions using Fourier-transform infrared (FTIR) spectroscopy. A remarkable observation was that two peaks at 1620 and 1690 cm−1 in Ala6 assigned to the intermolecular β-sheets were generated with increasing pressure. These peaks were not observed in Ala5. Our analyses of absorbance changes and frequency shifts further suggested that pressure was responsible for the PPII → β conformational change of Ala5, and the PPII → intermolecular β-sheet structure of Ala6, respectively. These results indicated a differing conformational stability of Ala5 under high pressure as compared with Ala6.
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