Isolation and characterization of ω-gliadin fractions

Abstract ω-Gliadins of Cappelle wheat were isolated by a two-step fractionation of gliadin: ω-gliadin was isolated by chromatography on sulfoethyl-Sephadex, then fractionated by chromatography on sulfoethylcellulose. Seven of the eight fractions isolated gave only one major constituent upon starch gel electrophoresis at pH 3.2. The heterogeneity of those constituents, revealed upon electrophoresis at alkaline pH, was shown to result from “in vitro” deamidation. ω-Gliadins can be distributed among three groups on the basis of their nitrogen content, molecular weight, N-terminal amino acid and amino acid compositions. The molecular weights of ω-gliadins, determined by gel filtration were found to be in the range 64 000–80 000 and the N-terminal amino acids of the three groups are alanine, threonine and serine. The amino acid compositions are characterized by very high glutamine contents since several ω-gliadins have glutamine contents higher than 55% residues. The similarities of the amino acid compositions lead us to consider the constituents belonging to each of the three groups as the expressions of homologous genes located on homeologous chromosomes of the wheat genome.