An enkephalin is a pentapeptide involved in regulating nociception in the body. The enkephalins are termed endogenous

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...

s, as they are internally derived and bind to the body's

opioid receptors Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatosta ...

. Discovered in 1975, two forms of enkephalin have been found, one containing

leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- ...

("leu"), and the other containing methionine ("met"). Both are products of the proenkephalin

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

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

Leu-enkephalin Leu-enkephalin is an endogenous opioid peptide neurotransmitter with the amino acid sequence Tyr-Gly-Gly-Phe-Leu that is found naturally in the brains of many animals, including humans. It is one of the two forms of enkephalin; the other is met-e ...

has Tyr-Gly-Gly-Phe-Leu.

Endogenous opioid peptides

There are three well-characterized families of opioid peptides produced by the body: enkephalins,

B-endorphin ''beta''-Endorphin (β-endorphin) is an endogenous opioid neuropeptide and peptide hormone that is produced in certain neurons within the central nervous system and peripheral nervous system. It is one of three endorphins that are produced in ...

, 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 Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like th ...

, which in the human body performs as an important signaling molecule in the brain. Enkephalins are found in high concentration in the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

as well as in the cells of adrenal medulla. In response to pain,

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad ...

, a

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

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 The hippocampus (via Latin from Greek , ' seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, ...

and

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA ...

. This research has suggested that, as part of the stress response, several met-enkephalin analogs have increased activity in the

, 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

The receptors for enkephalin are the

delta opioid receptor Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D ( NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may als ...

s and mu opioid receptors. Opioid receptors are a group of

G-protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related p ...

s, with other

opioid Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioi ...

s as

s as well. The other endogenous

opioids Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid us ...

are dynorphins (that bind to kappa receptors),

endorphin Endorphins (contracted from endogenous morphine) are chemical signals in the brain that block the perception of pain and increase feelings of wellbeing. They are produced and stored in an area of the brain known as the pituitary gland. Hist ...

s (mu receptors), endomorphins, and nociceptin/orphanin FQ. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs).

References

External links

* * Opioid peptides Pentapeptides {{biochemistry-stub

Endogenous opioid peptides

Effects on stress

Enkephalin receptor

See also

References

External links