Disulphide bonds of adjacent cysteine residues in low molecular weight subunits of wheat glutenin

The adjacent cysteine residues C-f1 and C-f2 located in the homologous sequence division III of LMW subunits of glutenin, and of alpha- and gamma-gliadins are important elements of the disulphide structure of these proteins. Two different analytical approaches were used to assign the disulphide linkages of the -Cys-Cys- sequence found in four cystine-containing peptides derived from LMW subunits of glutenin. Direct Edman degradation of the acetylated and cyanogen bromide treated peptide with detection of di-PTH-cystine was one method. Partial reduction of peptides with Tris(2-carboxyethyl)phosphine hydrochloride, subsequent separation of fragments by RP-HPLC, alkylation with iodoacetamide and sequence analysis was the second method. Both these methodologies gave identical results. It was shown that the first of the adjacent cysteines (C-f1) is linked with another cysteine residue of division III (C-c) and that the second one of the pair (C-f2) is linked with a cysteine residue in the C-terminal division V (C-y) of the primary structure. A model for the complete disulphide structure of LMW subunits is presented. (C) 1998 Academic Press Limited.