The purification and N-terminal amino acid sequence analysis of the high molecular-weight gluten polypeptides of wheat

Nine high molecular weight gluten subunits have been purified from cultivars of bread wheat (Triticum aestivum). They have broadly similar amino acid compositions with 34–39 mol% Glx, 12–17 mol% Pro and 14–19 mol% Gly. Some differences in the contents of other amino acids were apparent; notably cysteine varied from 0.4 to 1.5 mol%. On the basis of these compositions, the peptide maps with V8 proteinase and N-terminal amino acid sequences the subunits could be divided into four groups. Two of these contained subunits encoded by structural loci on chromosomes 1A and 1B, respectively, while the other two probably represented the products of two subfamilies of genes at a single locus on chromosome 1D. The N-terminal amino acid sequences were homologous, but differed in substitutions of single amino acids and in deletions of three and seven amino acids. Two subunits purified from Triticum monococcum and Aegilops squarrosa had N-terminal sequences closely related or identical to those of the 1A subunits and one group of 1D subunits respectively. Two cysteine residues were present in the N-terminal sequences of all the subunits, but the distances between these were affected by the deletions and varied from 7 to 14 residues. The results are discussed in relation to the ability of the subunits to form elastic disulphide-linked aggregates, and the importance of these in the structure and functionality of gluten.