Opioid peptides

class=skin-invert-image|thumb|Chemical structure of met-enkephalin

An enkephalin is a pentapeptide involved in regulating nociception (pain sensation) in the body. The enkephalins are termed endogenous ligands, as they are internally derived (and therefore endogenous) and bind as ligands to the body's opioid receptors. 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: Met-enkephalin is Tyr-Gly-Gly-Phe-Met. Leu-enkephalin is Tyr-Gly-Gly-Phe-Leu.

Dynorphins (Dyn) are a class of opioid peptides that arise from the precursor protein prodynorphin. When prodynorphin is cleaved during processing by proprotein convertase 2 (PC2), multiple active peptides are released: dynorphin A, dynorphin B, and α/β-neoendorphin. Depolarization of a neuron containing prodynorphin stimulates PC2 processing, which occurs within synaptic vesicles in the presynaptic terminal. Occasionally, prodynorphin is not fully processed, leading to the release of big dynorphin, a 32-amino acid molecule consisting of both dynorphin A and dynorphin B.

class of peptides that bind to opioid receptors

β-Endorphin (beta-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 humans, the others being α-endorphin and γ-endorphin.

Opiorphin is an endogenous chemical compound first isolated from human saliva. Initial research with mice shows the compound has a painkilling effect greater than that of morphine. It works by stopping the normal breakup of enkephalins, natural pain-killing opioids in the spinal cord. It is a relatively simple molecule consisting of a five-amino acid polypeptide, Gln-Arg-Phe-Ser-Arg (QRFSR).

Dermorphin is a hepta-peptide first isolated from the skin of South American frogs belonging to the genus Phyllomedusa. The peptide is a natural opioid that binds as an agonist with high potency and selectivity to mu opioid receptors. Dermorphin is about 30–40 times more potent than morphine. The amino acid sequence of dermorphin is H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2.

Nociceptin/orphanin FQ (N/OFQ), a 17-amino acid neuropeptide, is the endogenous ligand for the nociceptin receptor (NOP, ORL-1). Nociceptin acts as a potent anti-analgesic, effectively counteracting the effect of pain-relievers; its activation is associated with brain functions such as pain sensation and fear learning.

γ-Endorphin (gamma-endorphin) is an opioid peptide that is characterized by the presence of 17 amino acids. The first 16 amino acids are identical to α-endorphin; leucine added at the end. In addition, γ-endorphin is identical to the first 17 amino acids of β-endorphin. Similar to other endorphins, research focusing upon γ-endorphin has been ongoing since its discovery in the 1970s. Yet, most of the information about the substance's exact role within the body is speculation that has yet to be proven. Some studies have indicated, however, that the polypeptide has antipsychotic effects on a cert

Met-enkephalin, also known as metenkefalin (INN), sometimes referred to as opioid growth factor (OGF), is a naturally occurring, endogenous opioid peptide that has opioid effects of a relatively short duration. It is one of the two forms of enkephalin, the other being leu-enkephalin. The enkephalins are considered to be the primary endogenous ligands of the δ-opioid receptor, due to their high potency and selectivity for the site over the other endogenous opioids.

Adrenorphin, also sometimes referred to as metorphamide, is an endogenous, C-terminally amidated, opioid octapeptide (Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-NH2, YGGFMRRV-NH2) that is produced from proteolytic cleavage of proenkephalin A and is widely distributed throughout the mammalian brain. It was named based on the fact that it was originally detected in human phaeochromocytoma tumour derived from the adrenal medulla, and was subsequently found in normal human and bovine adrenal medulla as well. Adrenorphin exhibits potent opioid activity, acting as a balanced μ- and κ-opioid receptor agonist wh

chemical compound

chemical compound

Difelikefalin, sold under the brand name Korsuva, is an opioid peptide used for the treatment of moderate to severe itch. It acts as a peripherally-restricted, highly selective agonist of the κ-opioid receptor (KOR).

Exorphins are exogenous opioid peptides, distinguished from endorphins, or endogenous opioid peptides.

α-Endorphin (alpha-endorphin) is an endogenous opioid peptide with a length of 16 amino acids, and the amino acid sequence: Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr. Researchers at the Salk Institute were pioneers in isolating, sequencing, and synthesizing the peptides they named α- and γ-endorphin, and they determined that they had morphinomimetic activity. With the use of mass spectrometry and dansyl-Edman methods, Nicholas Ling, one of the researchers from the Salk Institute, was able to determine the primary sequence of α-endorphin.

Valorphin, also known as VV-hemorphin-5, is a naturally occurring, endogenous opioid heptapeptide of the hemorphin family with the amino acid sequence H-Val-Val-Tyr-Pro-Trp-Thr-Gln-OH (VVYPWTQ). It is produced in the body via proteolyic cleavage of residues 33-39 of the β-chain of hemoglobin. Valorphin binds preferentially to the μ-opioid receptor and produces effects such as analgesia and self-administration in animals. It also possesses cytotoxic and antiproliferative properties against tumor cells, the mediation of which, because they are reversed by naloxone, appears to be dependent on the

Gliadorphin-7 (also known as gluteomorphin) is an opioid peptide that is formed during digestion of the gliadin component of the gluten protein. It is usually broken down into amino acids by digestion enzymes. It has been hypothesized that children with autism have abnormal leakage from the gut of this compound. This is partly the basis for the gluten-free, casein-free diet. Abnormally high levels of gliadorphin have been found in the urine of autistic children via mass spectrometry testing.

Spinorphin is an endogenous, non-classical opioid peptide of the hemorphin family first isolated from the bovine spinal cord (hence the prefix spin-) and acts as a regulator of the enkephalinases, a class of enzymes that break down endogenous the enkephalin peptides. It does so by inhibiting the enzymes aminopeptidase N (APN), dipeptidyl peptidase III (DPP3), angiotensin-converting enzyme (ACE), and neutral endopeptidase (NEP). Spinorphin is a heptapeptide and has the amino acid sequence Leu-Val-Val-Tyr-Pro-Trp-Thr (LVVYPWT). It has been observed to possess antinociceptive, antiallodynic, and

Morphiceptin is a tetrapeptide (Tyr-Pro-Phe-Pro-NH2) that is a selective μ-opioid receptor agonist. It is derived from β-casomorphin and has over 1,000 times selectivity for μ- over δ-opioid receptors. When injected intracerebroventricularly (into the ventricular system of the brain), morphiceptin had an analgesic ED50 of 1.7 nmol per animal. The analgesic effects of morphiceptin were reversed by naloxone, meaning that the analgesic effect is mediated by the μ-opioid receptor.

DADLE ([D-Ala2, D-Leu5]-Enkephalin) is a synthetic opioid peptide with analgesic properties. Although it is often considered a selective δ-opioid receptor agonist, it also binds to the μ1 subtype of μ-opioid receptors.

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-enkephalin. The tyrosine residue at position 1 is thought to be analogous to the 3-hydroxyl group on morphine. Leu-enkephalin has agonistic actions at both the μ- and δ-opioid receptors, with significantly greater preference for the latter. It has little to no effect on the κ-opioid receptor.

Hemorphin-4 is an endogenous opioid peptide of the hemorphin family which possesses antinociceptive properties and is derived from the β-chain of hemoglobin in the bloodstream. It contains a tetrapeptide core with the amino acid sequence Tyr-Pro-Trp-Thr. Hemorphin-4 serves as a opioid receptor ligand that has affinities for the μ-, δ-, and κ-opioid receptors in the same range as the structurally related β-casomorphins, although affinity to the κ-opioid receptor is markedly higher in comparison. It acts as an agonist at these sites. It presents high affinity for other receptors such as angioten

The rubiscolins are a group of opioid peptides that are formed during digestion of the ribulose bisphosphate carboxylase/oxygenase (Rubisco) protein from spinach leaves. Two of them are known, acting as weak agonists of the delta opioid receptor selective for the G protein signaling pathway.

chemical compound

Amidorphin is an endogenous, C-terminally amidated, opioid peptide generated as a cleavage product of proenkephalin A in some mammalian species; in humans and most other species, the peptide is 1 residue longer and is not amidated. Amidorphin is widely distributed in the mammalian brain, with particularly high concentrations found in the striatum, and outside of the brain in adrenal medulla and posterior pituitary. The 26-residue peptide named amidorphin is found in several species including bovine (Bos taurus), sheep (Ovis aries), and pig (Sus scrofa). Humans and commonly studied lab animals

Leumorphin, also known as dynorphin B1–29, is a naturally occurring endogenous opioid peptide. Derived as a proteolytic cleavage product of residues 226-254 of prodynorphin (preproenkephalin B), leumorphin is a nonacosapeptide (29 amino acids in length) and has the sequence Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Gln-Phe-Lys-Val-Val-Thr-Arg-Ser-Gln-Glu-Asp-Pro-Asn-Ala-Tyr-Ser-Gly-Glu-Leu-Phe-Asp-Ala. It can be further reduced to dynorphin B (dynorphin B-13) and dynorphin B-14 by pitrilysin metallopeptidase 1 (formerly referred to as "dynorphin-converting enzyme"), an enzyme of the endopeptidase family. Le

DAMGO ([D-Ala2, N-MePhe4, Gly-ol]-enkephalin) is a synthetic opioid peptide with high μ-opioid receptor specificity. It was synthesized as a biologically stable analog of δ-opioid receptor-preferring endogenous opioids, leu- and met-enkephalin. Structures of DAMGO bound to the μ opioid receptor reveal a very similar binding pose to morphinans.