Gluten exorphin C

Abstract
A novel opioid peptide, Tyr‐Pro‐Ile‐Ser‐Leu, was isolated from the pepsin‐trypsin‐chymotrypsin digest of wheat gluten. Its IC50 values were 40 μM and 13.5 μM in the GPI and MVD assays, respectively. This peptide was named gluten exorphin C. Gluten exorphin C had a structure quite different from any of the endogenous and exogenous opioid peptides ever reported in that the N‐terminal Tyr was the only aromatic amino acid. The analogs containing Tyr‐Pro‐X‐Ser‐Leu were synthesized to study its structure‐activity relationship. Peptides in which X was an aromatic amino acid or an aliphatic hydrophobic amino acid had opioid activity.