7 Spectroscopic studies of high molecular weight subunits of wheat gluten.

P. S. BELTON. Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney Lane, Norwich, Norfolk NR4 7UA, UK.

Studies of the structure and dynamics of high molecular weight subunits were made, using high resolution NMR, NMR relaxation time, FTIR and CD. In solution, the protein repeat unit shows a ?-turn structure, while the N and ,C termini tend to form ?-helix. In the solid state more complex behaviour is observed. FTIR measurements of repetitive peptides show very little structure when dry. As the hydration level increases ?-sheet structures form. The sheet content then decreases and hydrated turn structures appear. Proton and carbon solid state magic angle spinning NMR show increased resolution with hydration but a population of glutamine amide groups are observed which are not in exchange with water on the NMR time scale. These are assumed to be from sheet structures. NMR relaxation time measurements show two populations, the ratios being dependent on hydration and temperature. It is assumed that the glutamine rich repeat units are able to form interchain hydrogen bonded networks with a ?-sheet structure. On hydration, hydrogen bonding with water forms regions of hydrated extended turns but not all interchain bonds are broken, bonded regions remaining together with unbonded regions. These regions, termed “Trains and Loops” respectively, are implicated in the viscoelastic properties of the subunits since the restoration of the loop/train equilibrium will be a restoring force when extension causes the breaking of interchain hydrogen bonds and loop distortion.