Gluten exorphin C is an opioid peptide derived from wheat gluten. Its IC₅₀ values are 40 μM and 13.5 μM for μ opioid and δ opioid activities in the GPI and MVD assays, respectively. IC50 & Target: IC50: 40 μM (μ opioid), 13.5 μM (δ opioid)^[1] In Vitro: Gluten exorphin C, a novel opioid peptide, is isolated from the pepsin-trypsin-chymotrypsin digest of wheat gluten. Gluten exorphin C is evaluated its opioid activities by the GPI and MVD assays and its receptor affinities by radioreceptor assays. Its IC₅₀s are 40 μM and 13.5 μM in the GPI and the MVD assays, respectively. Gluten exorphin C has a structure quite different from any of the endogenous and exogenous opioid peptides ever reported in that the N terminal Tyr is the only aromatic amino acid. The analogs containing Tyr-Pro-X-Ser-Leu are synthesized to study its structure-activity relationship. Peptides in which X is an aromatic amino acid or an aliphatic hydrophobic amino acid has opioid activity^[1].