FOURIER-TRANSFORM IR SPECTROSCOPIC STUDY OF HYDRATION-INDUCED STRUCTURE CHANGES IN THE SOLID-STATE OF OMEGA-GLIADINS

The hydration of omega-gliadins and partly deamidated and esterified o mega-gliadins has been studied by Fourier transform IR spectroscopy. T he secondary structure of the fully hydrated proteins was a mixture of beta-turns and extended chains, with a small amount of intermolecular beta-sheets. The absorption of the glutamine side chain amide groups contributed considerably to the amide I band with two well-defined pea ks at 1658 and 1610 cm(-1) The amide I band of the dry native sample c ould not be resolved into single component bands. There the backbone s tructure seemed to be distorted by extensive hydrogen bonding involvin g glutamine side chains. With increasing water content, these hydrogen bonds were broken successively by water molecules, resulting in an in crease in extended: hydrated structures, which gave rise to the format ion of intermolecular beta-sheet structures. Above 35 % (w/w) water th e beta-sheet content fell sharply and was replaced by extensively hydr ated extended structures. An amide I band similar to dissolved poly-L- proline proved that parts of the polymer were in a solution-like state . The replacement of many glutamine side chains in the esterified prot ein produced more resolved secondary structures even in the dry sample . The beta-sheet content of the dry sample was higher than in the nati ve omega-gliadins, but hydration generally caused very similar changes . At all hydration levels the spectra indicated a more ordered structu re than in the native sample. Overall, the modification caused changes that go beyond the simple presence or absence of glutamine bands.