Enkephalin

Overview
An enkephalin is a pentapeptide involved in regulating pain and nociception in the body. The enkephalins are termed endogenous ligands, or specifically endorphins, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin were revealed, one containing leucine ("leu"), while the other contains methionine ("met"). Both are products of the proenkephalin gene.


 * Met-enkephalin is Tyr-Gly-Gly-Phe-Met.
 * Leu-enkephalin has Tyr-Gly-Gly-Phe-Leu.

Endogenous opioid peptides
There are three well-characterized families of opioid peptides produced by the body: enkephalins, endorphins and dynorphins. The met-enkephalin peptide sequence is coded for by both the enkephalin gene and the endorphin gene (also known as the POMC gene) and that the leu-enkephalin peptide sequence is coded for by both the enkephalin gene and the dynorphin gene.

Enkephalin receptor
The receptors for enkephalin are the opioid receptors. These are a group of G-protein coupled receptors, with other opioids as ligands as well. The other endogenous opioids are dynorphins, endorphins, endomorphins and nociceptin/orphanin FQ. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs).