Editing Enkephalin

{{Short description|Pentapeptide}}
{{infobox protein
|Name=
|caption=Met-enkephalin 3D structure, alpha-carbons shown as balls and labeled by residue.<ref name="pmid14990485">{{PDB|1plx}}; {{cite journal | vauthors = Marcotte I, Separovic F, Auger M, Gagné SM | title = A multidimensional 1H NMR investigation of the conformation of methionine-enkephalin in fast-tumbling bicelles | journal = Biophys. J. | volume = 86 | issue = 3 | pages = 1587–600 |date=March 2004 | pmid = 14990485 | pmc = 1303993 | doi = 10.1016/S0006-3495(04)74226-5 | bibcode=2004BpJ....86.1587M}}</ref>
|image=Met-enkephalin 1plx model 1.png
|width=
|HGNCid=8831
|Symbol=PENK
|AltSymbols=
|EntrezGene=5179
|OMIM=131330
|RefSeq=NM_006211
|UniProt=P01210
|PDB=
|ECnumber=
|Chromosome=8
|Arm=q
|Band=23
|LocusSupplementaryData=-q24
}}

An '''enkephalin''' is a [[peptide|pentapeptide]] involved in regulating [[nociception]] (pain sensation) in the body.  The enkephalins are termed endogenous [[ligand]]s, as they are internally derived (and therefore [[endogenous]]) and bind as [[ligand]]s to the body's [[opioid receptor]]s.  Discovered in 1975, two forms of enkephalin have been found, one containing [[leucine]] ("leu"), and the other containing [[methionine]] ("met"). Both are products of the proenkephalin [[gene]].<ref name="pmid6281660">{{cite journal | vauthors = Noda M, Teranishi Y, Takahashi H, Toyosato M, Notake M, Nakanishi S, Numa S | title = Isolation and structural organization of the human preproenkephalin gene | journal = Nature | volume = 297 | issue = 5865 | pages = 431–4 |date=June 1982 | pmid = 6281660 | doi =10.1038/297431a0 |bibcode = 1982Natur.297..431N | s2cid = 4371340 }}</ref>
* [[Met-enkephalin]] is Tyr-Gly-Gly-Phe-'''Met'''.
* [[Leu-enkephalin]] is Tyr-Gly-Gly-Phe-'''Leu'''.

==Endogenous opioid peptides==
There are three well-characterized families of [[Opioid peptide#Opioid peptides produced by the body|opioid peptides produced by the body]]: enkephalins, [[β-endorphin]], and [[dynorphins]]. 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.<ref>[http://drugabuse.gov/pdf/monographs/70.pdf Opioid peptides: Molecular pharmacology, biosynthesis and analysis] {{Webarchive|url=https://web.archive.org/web/20090826150330/http://drugabuse.gov/pdf/monographs/70.pdf |date=2009-08-26 }}, R.S. Rapaka and R. L. Hawks (editors) in a [[National Institute on Drug Abuse]] Research Monograph (#70), 1986.</ref> 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.{{cn|date=July 2024}}

==Effects on stress==

Enkephalin is also considered a [[neuropeptide]], which in the human body performs as an important signaling molecule in the brain. Enkephalins are found in high concentration in the [[Human brain|brain]] as well as in the cells of [[adrenal medulla]]. In response to pain, [[norepinephrine]], a [[hormone]] that is activated in fight-or-flight response, is released along with [[endorphins]].<ref>{{cite journal | title = Endorphins | first = Gavril W. | last = Pasternak | name-list-style = vanc | journal = AccessScience | doi = 10.1036/1097-8542.232500 }}</ref> A 2017 study indicates that this polypeptide may be linked to brain functioning during the [[stress response]], especially in the [[hippocampus]] and [[prefrontal cortex]]. This research has suggested that, as part of the stress response, several met-enkephalin analogs have increased activity in the [[hippocampus]], while leu-enkephalin analogs as well as [[somatostatin]]s are [[downregulation|downregulated]] during stress. Stressors may impact neuropeptides whose action is localized to a specific brain region.<ref name="Henry_2017">{{cite journal | vauthors = Henry MS, Gendron L, Tremblay ME, Drolet G | title = Enkephalins: Endogenous Analgesics with an Emerging Role in Stress Resilience | journal = Neural Plasticity | volume = 2017 | pages = 1546125 | date = 2017 | pmid = 28781901 | pmc = 5525068 | doi = 10.1155/2017/1546125 | doi-access = free }}</ref>

==Enkephalin receptor==
{{Main|Opioid receptor}}
The receptors for enkephalin are the [[delta opioid receptor]]s and [[mu opioid receptor]]s. Opioid receptors are a group of [[G-protein-coupled receptor]]s, with other [[opioid]]s as [[ligand]]s as well. The other [[endogenous]] [[opioids]] are [[dynorphin]]s (that bind to kappa receptors), [[endorphin]]s (mu receptors), [[endomorphins]], and [[nociceptin|nociceptin-orphanin]] FQ. The opioid receptors are ~40% identical to [[somatostatin]] [[receptor (biochemistry)|receptor]]s (SSTRs).{{Citation needed|date=September 2019}}

==See also==
* [[Endorphin]]
* [[Enkephalinase]]
* [[Opioid peptide]]
* [[Racecadotril]]
* [[RB-101]]

==References==
{{Reflist|2}}

==External links==
* {{MeshName|Enkephalins}}
* {{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 6/6ch2/s6ch2_36 |chapter-url=http://humanphysiology.tuars.com/program/section6/6ch2/s6ch2_36.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section6/6ch2/s6ch2_36.htm|archive-date=2016-03-24}}

{{Opioid peptides}}
{{Opioidergics}}
{{Chocolate}}

[[Category:Opioid peptides]]
[[Category:Pentapeptides]]