Pressure-tuning FT-IR spectroscopic study on the helix-coil transition of Ala-rich oligopeptide in aqueous solution

We investigated the effect of pressure on the helix-coil transition of an Ala-rich peptide (AK16: YGAAKAAAAKAAAAKA-NH2) in aqueous solution by FT-IR spectroscopy. The spectra of the amide I' region of AK16 in aqueous solution was decomposed into some component bands using a curve fitting method. The peak at around 1635 cm −1 corresponding to the solvent exposed α-helix conformer increases with increasing pressures, while the peak at around 1655 cm −1 corresponding to the random coil conformer decreases. From the pressure dependence of the band intensities, we determined the volume change from the α-helix to random coil conformers of AK16 to be + 10.5 ± 0.3 cm3/mol. The positive volume change is different from the negative volume change generally observed in the pressure denaturation of proteins.