Partial product ion mass spectrum of the 35-mer gliadin peptide (residues 198–232). The spectrum displays two series of peaks, the so-called b-ions and y-ions, that allow the sequence to be elucidated. A part of the y-ion series consists of the masses 857.5, 985.5, 1,084.5, and 1,171.6, which correspond to the partial sequence Glutamine/Lysine (Q/K),Valine (V), Serine (S). This information, together with the total mass of the 35-mer peptide (3,897 Da), was put in the program peptidesearch. This led to several hits, but only one gliadine-related peptide was found, gda09 198–232. In a similar fashion, the peptide sequences of the 2,479- and 2,679-Da peaks (Fig. 1C) were elucidated. These peaks were found to represent gliadin residues 3–24 (sequence VPVPQLQPQNPSQQQPQEQVPL) and glutenin residues 50–72 (sequence SQQQQPPFSQQQPPFSQQELPIL).