Gliadin is a gluten component. This peptide is derived from amino acid residues 57-68 of a9-gliadin and represents an immunodominant epitope that has been shown to elicit HLA-DQ2-restricted T-cell responses in celiac patients. This epitope is resistant to pancreatic proteolysis.
Pyroglutamyl (pGlu) peptides may spontaneously form when either Glutamine (Q) or Glutamic acid (E) is located at the sequence N-terminus. The conversion of Q or E to pGlu is a natural occurrence and in general it is believed that the hydrophobic γ-lactam ring of pGlu may play a role in peptide stability against gastrointestinal proteases. Pyroglutamyl peptides are therefore considered a normal subset of such peptides and are included as part of the peptide purity during HPLC analysis.