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Opioid Peptides are short sequences of amino acids which mimic the effect of opiates in the brain. Opioid peptides may be produced by the body itself, for example endorphins, or be absorbed from partially digested food (casomorphins, exorphins and rubiscolins). The effect of these peptides vary, but they all resemble opiates. The opioid food peptides have lengths of typically 4-8 amino acids. The body's own opioids are generally much longer.
Opioid peptides produced by the body
The human genome contains three homologous genes that are known to code for endogenous opioid peptides. Each gene codes for a large protein that can be processed to yield smaller peptides that have opiate-like activity.
- The nucleotide sequence of the human gene for proopiomelanocortin (POMC) was characterized in 1980. The POMC gene codes for endogenous opiates such as β-endorphin and gamma-endorphin. The peptides with opiate activity that are derived from proopiomelanocortin comprise the class of endogenous opioid peptides called "endorphins".
- The human gene for enkephalins was isolated and its sequence described in 1982.
- The human gene for dynorphins (originally called the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983.
- Opiorphin, found in human saliva, is an enkephalinase inhibitor, i.e. it prevents the metabolism of enkephalins.
Opioid food peptides
- Casomorphin (from milk)
- Gluten exorphin (from gluten)
- Gliadorphin/gluteomorphin (from gluten)
- Rubiscolin (from spinach)
References & Bibliography
- Chang AC, Cochet M, Cohen SN. "Structural organization of human genomic DNA encoding the pro-opiomelanocortin peptide." Proceedings of the National Academy of Sciences 1980 Aug;77(8):4890-4. PMID 6254047
- Ling N, Burgus R, Guillemin R. "Isolation, primary structure, and synthesis of α-endorphin and γ-endorphin, two peptides of hypothalamic-hypophysial origin with morphinomimetic activity." Proceedings of the National Academy of Sciences 1976 Nov;73(11):3942-6. PMID 1069261
- Noda M, Teranishi Y, Takahashi H, Toyosato M, Notake M, Nakanishi S, Numa S. "Isolation and structural organization of the human preproenkephalin gene." Nature 1982 Jun 3;297(5865):431-4. PMID 6281660
- Horikawa S, Takai T, Toyosato M, Takahashi H, Noda M, Kakidani H et al. "Isolation and structural organization of the human preproenkephalin B gene." Nature Nature. 1983 Dec 8-14;306(5943):611-4. PMID 6316163