Enkephalin

Endogenous opioid peptides

There are three well-characterized families of 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. 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.

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 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. 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 somatostatins are downregulated during stress. Stressors may impact neuropeptides whose action is localized to a specific brain region.

Enkephalin receptor

Main article: Opioid receptor

The receptors for enkephalin are the delta opioid receptors and mu opioid receptors. Opioid receptors are a group of G-protein-coupled receptors, with other opioids as ligands as well. The other endogenous opioids are dynorphins (that bind to kappa receptors), endorphins (mu receptors), endomorphins, and nociceptin-orphanin FQ. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs).

References

References

1. (March 2004). "A multidimensional 1H NMR investigation of the conformation of methionine-enkephalin in fast-tumbling bicelles". Biophys. J..
2. (June 1982). "Isolation and structural organization of the human preproenkephalin gene". Nature.
3. [http://drugabuse.gov/pdf/monographs/70.pdf Opioid peptides: Molecular pharmacology, biosynthesis and analysis] {{Webarchive. link. (2009-08-26 , R.S. Rapaka and R. L. Hawks (editors) in a [[National Institute on Drug Abuse]] Research Monograph (#70), 1986.)
4. Pasternak, Gavril W.. "Endorphins". AccessScience.
5. (2017). "Enkephalins: Endogenous Analgesics with an Emerging Role in Stress Resilience". Neural Plasticity.