Direct evidence that the number and location of cysteine residues affect glutenin polymer structure

In this study, the possible roles of three well-characterised model prolami ns in the structure of the glutenin macropolymer were examined. Model prola mins were labelled with fluorescein isothiocyanate (FITC), and incorporated into the glutenin macropolymer of a base flour using a partial reduction-o xidation scheme. The effect of incorporation of the model prolamins on doug h behaviour was determined by assessing differences in polymer size distrib ution, mixing properties, and distribution of the model prolamins in a doug h after incorporation. Using this approach, the prolamins capable of formin g inter-chain disulphide bonds were shown to be incorporated into the glute nin macropolymer while prolamins that were not capable of forming inter-cha in disulphide bonds were retained as monomers. The distribution of fluoresc ently-labelled prolamins after their incorporation into the glutenin macrop olymer of the dough was examined by confocal light scanning microscopy, in order to determine the possible roles of omega-gliadins and glutenin-like s ubunits with varied cysteine residue compositions in the structural organis ation. The role of the model prolamins was a function of the disulphide-bon ding capabilities of the polypeptides. Model omega-gliadins were retained a s monomers and functioned as space fillers; model glutenin-like subunits co ntaining a single cysteine residue incorporated into the glutenin macropoly mer but functioned as chain terminators; and model glutenin-like subunits c ontaining two cysteine residues incorporated into the glutenin macropolymer and acted as chain extenders.