D-GLUTENIN SUBUNITS - N-TERMINAL SEQUENCES AND EVIDENCE FOR THE PRESENCE OF CYSTEINE

The two-chromosome, 1D-coded D subunits of low molecular weight gluten ins from Chinese Spring wheat were purified by using preparative isoel ectric focusing and reversed-phase high-performance liquid chromatogra phy. Their N-terminal sequences corresponded to those of the two-chrom osome, 1D-coded omega-gliadins, which they also resemble in molecular weight and isoelectric point. In order to show the presence of cystein e in D subunits, which should account for their presence in glutenin, the reduced subunits were reacted with a fluorogenic reagent specific for sulfhydryl groups in a mixture with the 1D-controlled omega-gliadi ns that were assumed to have no cysteine residues. When the mixture wa s separated in a reversed-phase high-performance liquid chromatography system equipped with UV absorbance and fluorescence detectors in seri es, all components were detected by UV absorbance, but only the peaks corresponding to the D subunits showed fluorescence. This confirmed th e presence of at least one cysteine in the D glutenin subunits. If onl y one cysteine residue is present, which seems likely, it is possible that D subunits would negatively influence quality characteristics bec ause they would be able to form only intermolecular disulfide bonds, t hereby acting as terminators of the growing glutenin polymers.