 Met-enkephalin 3D structure, alpha-carbons shown as balls and labeled by residue.[1] | |||||||
| Identifiers | |||||||
|---|---|---|---|---|---|---|---|
| Symbol | PENK | ||||||
| NCBI gene | 5179 | ||||||
| HGNC | 8831 | ||||||
| OMIM | 131330 | ||||||
| RefSeq | NM_006211 | ||||||
| UniProt | P01210 | ||||||
| Other data | |||||||
| Locus | Chr. 8q23-q24 | ||||||
| |||||||
Anenkephalin is apentapeptide involved in regulatingnociception (pain sensation) in the body. The enkephalins are termed endogenousligands, as they are internally derived (and thereforeendogenous) and bind asligands to the body'sopioid receptors. Discovered in 1975, two forms of enkephalin have been found, one containingleucine ("leu"), and the other containingmethionine ("met"). Both are products of the proenkephalingene.[2]
There are three well-characterized families ofopioid peptides produced by the body: enkephalins,β-endorphin, anddynorphins. The met-enkephalin peptide sequence is coded for by the enkephalin gene; the leu-enkephalin peptide sequence is coded for by both the enkephalin gene and the dynorphin gene.[3] The proopiomelanocortin gene (POMC) also contains the met-enkephalin sequence on the N-terminus of beta-endorphin, but the endorphin peptide is not processed into enkephalin.[citation needed]
Enkephalin is also considered aneuropeptide, which in the human body performs as an important signaling molecule in the brain. Enkephalins are found in high concentration in thebrain as well as in the cells ofadrenal medulla. In response to pain,norepinephrine, ahormone that is activated in fight-or-flight response, is released along withendorphins.[4] A 2017 study indicates that this polypeptide may be linked to brain functioning during thestress response, especially in thehippocampus andprefrontal cortex. This research has suggested that, as part of the stress response, several met-enkephalin analogs have increased activity in thehippocampus, while leu-enkephalin analogs as well assomatostatins aredownregulated during stress. Stressors may impact neuropeptides whose action is localized to a specific brain region.[5]
The receptors for enkephalin are thedelta opioid receptors andmu opioid receptors. Opioid receptors are a group ofG-protein-coupled receptors, with otheropioids asligands as well. The otherendogenousopioids aredynorphins (that bind to kappa receptors),endorphins (mu receptors),endomorphins, andnociceptin-orphanin FQ. The opioid receptors are ~40% identical tosomatostatinreceptors (SSTRs).[citation needed]
