The conformations of wheat gluten proteins, II, aggregated gliadins and low molecular weight subunits of glutenin

Fractions containing low-molecular-weight (LMW) subunits of glutenin and aggregated gliadins were prepared from four cultivars of winter wheat that varied in their quality for breadmaking. The fractions were analysed by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and their amino acid compositions determined. Their secondary structures were studied by circular dichroism (cd) spectroscopy and the proportions of α-helix and β-sheet calculated from the spectra. These values were compared with the secondary structure content predicted from the published amino acid sequence of an aggregated gluten protein. When dissolved in 50% (v/v) aqueous propan-1-o1 at 20°C the proportions of a-helix varied from 34 to 37% and β-sheet from 18 to 24%, compared with calculated values of 37% et α-helix and 15% β-sheet. Heating to 80°C resulted in greater decreases in the secondary structure contents of the reduced LMW subunits of glutenin than of the unreduced aggregated gliadins, indicating that the latter were partially stabilized by the intact disulphide bonds. There were no major differences in the secondary structure contents or thermal stabilities of the fractions from the four cultivars. The cd spectra of both the aggregated gliadin and LMW subunit fractions were more similar to those of the α-, β- and γ-gliadins than to those of the ω-gliadins or high-molecular-weight (HMW) subunits of glutenin, which is consistent with their known amino acid sequence relationships.