An enkephalin is a peptide involved in regulating nociception (pain sensation) in the body. The enkephalins are termed endogenous , as they are internally derived (and therefore endogenous) and bind as to the body'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:
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.
[ Opioid peptides: Molecular pharmacology, biosynthesis and analysis , R.S. Rapaka and R. L. Hawks (editors) in a National Institute on Drug Abuse Research Monograph (#70), 1986.] 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
Human 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
are
downregulation during stress. Stressors may impact neuropeptides whose action is localized to a specific brain region.
Enkephalin 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
as
as well. The other
endogenous opioids are
(that bind to kappa receptors),
(mu receptors),
endomorphins, and
nociceptin FQ. The opioid receptors are ~40% identical to
somatostatin receptors (SSTRs).
See also
External links
