Conformational studies of peptides derived by the enzymic hydrolysis of a gamma-type gliadin

The secondary structures of γ₄₄ gliadin and peptides derived from it by enzymic hydrolysis were studied by circular dichroism spectroscopy. Two peptides, obtained by chymotryptic cleavage, broadly corresponding to the proline-rich repetitive N-terminal domain and to the proline-poor non-repetitive C-terminal domain respectively, were studied in detail. A cryogenic solvent system, ethanediol : water (2:1 v/v), was used to determine the cd spectra of the protein and peptides at temperatures down to − 100°C. The proline-rich repetitive peptide showed a spectrum typical of βI/III reverse turns at high-temperature, but a spectrum similar to that of the poly-L-proline II helix at −100 °C. The proline-poor non-repetitive peptide, however, showed an α-helical-type cd spectrum over the temperature range studied. The results are discussed in relation to the conformations of γ-gliadins.