database / hormone
Met-enkephalin
also known as opioid growth factor
Skeletal structure drawn from the computed atomic coordinates in PubChem CID 443363. Carbons are implicit vertices; hydrogens on carbon are suppressed, as in any structural formula. Nothing here is estimated — every atom sits where PubChem placed it.
Research reference only. The observations below are recorded in the cited literature. Nothing here is advice or a recommendation, and no dosing information is published on this site.
Sequence
YGGFM
Tyr-Gly-Gly-Phe-Met
- hydrophobic
- positive
- negative
- polar
- aromatic
- glycine
- proline
- cysteine
Computed backbone mass 573.66 Da agrees with PubChem's reported 573.7 Da (Δ 0.04 Da). Two independent sources agree on the primary structure.
Molecular data
| molecular formula | C27H35N5O7S |
|---|---|
| molecular weight | 573.7 Da (PubChem) |
| computed backbone mass | 573.66 Da |
| length | 5 residues |
| net charge (pH 7.4) | 0 |
| mean hydropathy | 0.52 |
| half-life | not characterised |
| delivery route | not characterised |
| PubChem CID | 443363 |
| PDB | not characterised |
| UniProt parent | P01210 |
Mechanism
Endogenous opioid pentapeptide; delta-opioid receptor preferring.
Reported targets: DOR MOR
Experimental structure
No experimental structure of this peptide is deposited in the PDB. Nothing is rendered here — a predicted fold would not be a structure, and this site does not draw one.
Position in the parent protein
…LPQDGTSTLRENSKPEESHLLAKRYGGFMKRYGGFMKKMDELYPMEPEEEANG…
Parent sequence from UniProt P01210. Released from proenkephalin.
Reported effects
Each row is an outcome described in the literature indexed for this peptide. Reported in the cited work — not a claim, not a recommendation.
| reported outcome | where it appears |
|---|---|
| analgesic signalling | Heat and cold stresses exert disparate effects on expression of proenkephali… Poultry science 2026 |
| immune modulation | Met-enkephalin modulates the stress responses of plasma concentrations of co… Frontiers in physiology 2025 |
Literature (8)
Heat and cold stresses exert disparate effects on expression of proenkephalin, and concentrations of Met-enkephalin in the hypothalamus, pituitary and adrenal glands, plasma concentrations Met-enkephalin, Leu-enkephalin, β-endorphin and corticosterone and opioid receptor binding in chickens — Poultry science 2026
abstract not reproduced — this record is not open-access, so it is linked rather than copied.
publisher record ↗ · PMID 42617248 · DOI 10.1016/j.psj.2026.107516
Met-enkephalin modulates the stress responses of plasma concentrations of corticosterone, delta opioid receptor binding, pro-enkephalin expression, and processing in chickens — Frontiers in physiology 2025
IntroductionMet-enkephalin is a neuropeptide whose release into the circulation is enhanced by stress. There have been no studies on the effects of peripherally administered Met-enkephalin in chickens.MethodsThe effects of peripheral administration of Met-enkephalin on the stress response in chickens were investigated measuring plasma concentrations of corticosterone and Met-enkephalin, together with expression of pro-enkephalin (PENK) and delta-opioid binding in the hypothalamus, anterior pituitary and adrenal glands.ResultsAdministration of Met-enkephalin was followed by decreases in the basal and stressed plasma concentrations of the principal glucocorticoid, corticosterone, in chickens. In addition, the increase in plasma concentrations of corticosterone evoked by restraint stress was markedly decreased when the birds were treated with Met-enkephalin. Administration of Met-enkephalin…
open access ↗ · PMID 41669367 · DOI 10.3389/fphys.2025.1736176
Correction: Met-enkephalin modulates the stress responses of plasma concentrations of corticosterone, delta opioid receptor binding, pro-enkephalin expression, and processing in chickens — Frontiers in physiology 2026
abstract not reproduced — this record is not open-access, so it is linked rather than copied.
publisher record ↗ · PMID 42630893 · DOI 10.3389/fphys.2026.1936355
Met-enkephalin and other opioid peptides in the stress response of chickens: lessons from laboratory animals and livestock — Frontiers in physiology 2026
abstract not reproduced — this record is not open-access, so it is linked rather than copied.
open access ↗ · PMID 41835143 · DOI 10.3389/fphys.2026.1756240
Peptide chirality and opioid receptor modulation: Hepatoprotective effect of d-Met-enkephalin in acetaminophen-induced liver injury — Acta pharmaceutica (Zagreb, Croatia) 2025
abstract not reproduced — this record is not open-access, so it is linked rather than copied.
publisher record ↗ · PMID 41527975 · DOI 10.2478/acph-2025-0036
Unraveling the role of iodide in photosensitized oxidation of Met-Enkephalin — Journal of photochemistry and photobiology. B, Biology 2026
abstract not reproduced — this record is not open-access, so it is linked rather than copied.
publisher record ↗ · PMID 42019119 · DOI 10.1016/j.jphotobiol.2026.113439
Research note: Peripheral administration of Met-enkephalin: Novel attenuation of the adrenal medullary and thyroidal stress responses in young female chickens — Poultry science 2025
Adrenal hormones play a critical response to stresses in poultry, livestock and other vertebrates. Moreover, there are stress effects on thyroid hormones. Plasma concentrations of epinephrine (EP), norepinephrine (NE), thyroxine (T4) and triiodothyronine (T3) were increased by restraint stress (placing pullets into a small cage in darkness) in 14-week-old pullets. There has been a complete dearth of publications on the effects of peripheral administered Met-enkephalin on endocrine systems in chickens. To remedy this, the effects of peripheral administration of Met-enkephalin per se was examined as was along with its ability to either potentiate or attenuate the responses to stress. Plasma concentrations of EP and NE were modestly increased in chickens receiving Met-enkephalin injection peripherally. The increase in plasma concentrations of EP, NE, T3 and T4 together with the decrease in …
open access ↗ · PMID 40896952 · DOI 10.1016/j.psj.2025.105748
Effects of Cholinergic and Opioid Antagonists on In Vitro Release of Met-Enkephalin, Somatostatin and Insulin-like Growth Factor-1 by and PENK Expression in Crop, Proventriculus and Duodenum of Newly Hatched Chickens — Animals : an open access journal from MDPI 2025
The gastrointestinal (GI) tract is under neural, endocrine and paracrine control. The release (basal and in the presence of either cholinergic and opioid antagonists) of Met-enkephalin, insulin-like growth factor 1 (IGF-1) and somatostatin (SRIF) was determined quantitatively in vitro using explants of the crop, proventriculus and duodenum from either day 0 or day 1 chicks. In addition, the effects of cholinergic and opioid antagonists on PENK gene expression were examined. Thus, the aim of this study was to determine the roles of cholinergic and opioid receptors in the GI tract in newly hatched chickens. Moreover, the effect of IGF-1 and Met-enkephalin on cell division in duodenal explants in vitro was determined. There was both the release of Met-enkephalin from, and PENK expression in, the explants of the crop, proventriculus and duodenum tissue. This is the first report of any neurop…
open access ↗ · PMID 40564255 · DOI 10.3390/ani15121702
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