Table 5.
Opioid peptides generated from the enzymatic hydrolysis of animal and plant proteins in the gastrointestinal tract
| Source | Name of opioid peptide | Amino acid sequence |
|---|---|---|
| Milk casein | Bovine β-casomorphin 1–3 | Tyr-Pro-Phe-OH |
| Bovine β-casomorphin 1–4 | Tyr-Pro-Phe-Pro-OH | |
| Bovine β-casomorphin 1–4, amide | Tyr-Pro-Phe-Pro-NH2 | |
| Bovine β-casomorphin 5 | Tyr-Pro-Phe-Pro-Gly-OH | |
| Bovine β-casomorphin 7 | Tyr-Pro-Phe-Pro-Gly-Pro-Ile-OH | |
| Bovine β-casomorphin 8 | Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-OHa | |
| Gluten protein | Gluten exorphin A5 | Gly-Tyr-Tyr-Pro-Thr-OH |
| Gluten exorphin B4 | Tyr-Gly-Gly-Trp-OH | |
| Gluten exorphin C | Tyr-Pro-Ile-Ser-Leu-OH | |
| Gliadorphin | Tyr-Pro-Gln-Pro-Gln-Pro-Phe-OH | |
| Soybean protein | Soymorphin-5b | Tyr-Pro-Phe-Val-Val-OH |
| Soymorphin-5, amide | Tyr-Pro-Phe-Val-Val-NH2 | |
| Soymorphin-6 | Tyr-Pro-Phe-Val-Val-Asn-OH | |
| Soymorphin-7 | Tyr-Pro-Phe-Val-Val-Asn-Ala-OH | |
| Spinach protein | Rubiscolin-5 | Gly-Tyr-Tyr-Pro-OH |
| Rubiscolin-6 | Gly-Tyr-Tyr-Pro-Thr-OH |
Adapted from Li-Chan [21], López-Barrios et al. [22], Shimizu and Son [35], Bah et al. [36], and Froetschel [42]
aAnother form of bovine β-casomorphin 8 has histidine instead of proline in position 8, depending on whether the peptide is derived from A1 or A2 beta-casein
bDerived from β-conglycinin β-subunit