Evidence for the presence of only one cysteine residue in the D-type low molecular weight subunits of wheat subunits of wheat glutenin

D-type low molecular weight subunits of bread wheat glutenin have omega-gli adin type N-terminal amino acid sequences, but are incorporated into the gl utenin polymers because of the presence of cysteine residues. In order to d etermine the number and position of cysteine residues, ID-encoded D-type lo w molecular weight subunits of wheat glutenin were purified from the cv. Ch inese Spring using a procedure thai allowed high recovery. Comparison of th e molecular weights of alkylated and unalkylated subunits by MALDI mass spe ctrometry indicated the presence of only one cysteine residue per molecule. This was supported also by the detection of dimers of D subunits in gluten . An internal sequence of 62 amino acids preceding the cysteine was obtaine d, but it was nor possible to identify the cysteine residue, either because it was nor within the range of N-terminal sequencing of peptides obtained, or because it was present in one of the two unidentified positions. (C) 19 99 Academic Press.