This is a working overview of melanocortin receptor, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-01-24 and is reviewed periodically as new material appears.
Melanotan II binds several melanocortin receptor subtypes rather than a single target. MC1R on melanocytes drives melanin synthesis, while MC3R and MC4R participate in energy balance, appetite, and sexual response pathways. This lack of selectivity explains why reported effects extend beyond skin darkening. Substitutions at positions four and seven, including norleucine and D-phenylalanine, increase potency and resistance to peptidases. Understanding which receptor mediates which effect remains an active area of investigation.
Published human data come mostly from small, short studies rather than large controlled trials. Reported outcomes include increased skin pigmentation and, in some reports, effects on appetite and libido, but sample sizes are small and follow-up is limited. Whether long-term use produces durable pigment changes or adverse effects is not established. Because products sold outside pharmacies are not standardized, the actual content of any given vial is often unknown. Independent testing of such material is uncommon.
Melanotan II is a synthetic cyclic heptapeptide analog derived from the core sequence of alpha-melanocyte-stimulating hormone. Researchers at the University of Arizona synthesized it during the 1980s while studying pigmentation and appetite signaling. The compound is not an approved medicine in any major jurisdiction and appears mainly in laboratory and research-chemical settings. Its structure incorporates a lactam bridge between side chains, which constrains the ring and slows enzymatic breakdown relative to the natural hormone.
The compound was developed in the late 1980s and early 1990s by academic researchers investigating melanocortin signaling and pigmentation. Early work explored whether synthetic analogs could reproduce effects of the natural hormone under controlled conditions. The molecule never advanced through the full regulatory pathway required for approval as a medicine. From the mid-2000s onward it appeared in unregulated consumer markets, often distributed through informal channels. That gap between research origins and commercial availability shapes how the compound is discussed today.
Melanotan-2 is a synthetic peptide designed as an analog of alpha-melanocyte-stimulating hormone, a signaling molecule produced in the pituitary and skin. Its structure is a linear chain of seven amino acids that folds into a ring through an internal lactam bridge joining two side chains. The compound is sometimes written as MT-II or MEL-2 in informal and commercial contexts. It belongs to the melanocortin peptide family, a group of short signaling molecules that share a conserved core sequence recognized by melanocortin receptors.
Two structural changes distinguish the synthetic peptide from the natural hormone. A norleucine residue replaces methionine at one position, and a D-configured phenylalanine replaces the natural L-form at another. Both substitutions slow enzymatic breakdown, which extends the molecule's persistence relative to the parent hormone. The lactam bridge further constrains the backbone into a stable conformation. These features are standard design strategies in peptide chemistry and are not unique to this compound; they appear across many research peptides built for improved stability.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Analog of alpha-melanocyte-stimulating hormone |
| Primary receptor family | Melanocortin receptors MC1R through MC5R | Binding is not subtype-selective |
| Development period | 1980s | Synthesized during pigmentation and appetite research |
| Regulatory status | Not an approved medicine | No major regulator has authorized human use |
| Related compound | Afamelanotide | Linear analog studied for photoprotection |
Activity is attributed to agonism at melanocortin receptors, particularly MC1R and MC4R. Activation of MC1R on melanocytes increases melanin synthesis, which underlies the reported tanning effect. MC4R engagement in the central nervous system is linked to appetite suppression and to effects on sexual arousal reported in early clinical studies. Those studies were small and were not designed to establish efficacy or long-term safety. Receptor selectivity among the melanocortin subtypes is not absolute, which complicates attribution of any effect to a single pathway.
Regulatory treatment varies between countries. Several national medicines agencies have classified the peptide as unapproved, and customs authorities in some jurisdictions seize shipments on that basis. A few jurisdictions channel supply through prescription-only frameworks that do not list the substance by name. Because the material circulates mainly through online vendors, composition and purity are rarely verified before sale. Surveys of unapproved peptide products have reported labels that did not match measured content in a substantial fraction of samples.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its sequence incorporates modified residues that increase potency and extend biological activity relative to the native hormone. The compound binds receptors of the melanocortin family and is examined mainly in laboratory research. It does not occur naturally and exists only as a manufactured chemical entity produced by solid-phase synthesis.
The peptide was developed during the 1980s by researchers investigating melanocortin signalling and skin pigmentation pathways. Early work focused on analogues of alpha-melanocyte-stimulating hormone that would resist enzymatic breakdown more effectively than the parent molecule. Melanotan-2 emerged from that programme as a shortened, cyclised variant. Reports describing its synthesis and receptor activity later appeared in the scientific literature. Commercial availability grew through unregulated channels rather than through pharmaceutical approval.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence incorporates a lactam bridge that constrains the peptide into a ring, which increases resistance to enzymatic breakdown relative to the natural hormone. Researchers at the University of Arizona synthesised the compound in the late 1980s and early 1990s while studying pigmentation pathways. It has never received marketing approval from any national medicines regulator. In the scientific literature it is usually described as a laboratory research reagent rather than a therapeutic product.
The peptide acts as a non-selective agonist at melanocortin receptors, showing affinity for MC1R, MC3R, MC4R and MC5R. Activation of MC1R on melanocytes drives the conversion of tyrosine into melanin and shifts production toward the darker eumelanin form. MC4R signalling in the central nervous system is linked to appetite and energy balance, which helps explain why reduced food intake appeared in early human studies. Effects on MC4R and on vascular tone also account for the erectile responses recorded as unexpected findings in those same trials.
Melanotan-2 is frequently confused with afamelanotide, a linear analogue authorised in the European Union for erythropoietic protoporphyria. The two compounds differ in chain length, ring structure and receptor selectivity, so findings for one cannot be transferred directly to the other. Published controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports. Questions about effect size, dose-response behaviour and long-term safety therefore remain unresolved.
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More data on this classification are discoverable at the Expasy metallothionein page.Secondary structure elements have been observed in several MTs SmtA from Syneccochoccus, mammalian MT3, echinoderm SpMTA, fish Notothenia coriiceps MT, crustacean MTH, but until this moment, the content of such structures is considered to be poor in MTs, and its functional influence is not considered. Tertiary structure of MTs is also highly heterogeneous. While vertebrate, echinoderm and crustacean MTs show a bidominial structure with divalent metals as Zn(II) or Cd(II) (the protein is folded so as to bind metals in two functionally independent domains, with a metallic cluster each), yeast and prokaryotic MTs show a monodominial structure (one domain with a single metallic cluster). In yeast, the first 40 residues in the protein wrap around the metal by forming two large parallel loops separated by a deep cleft containing the metal cluster. Although no structural data is available for molluscan, nematoda and Drosophila MTs, it is commonly assumed that the former are bidominial and the latter monodominial. No conclusive data are available for Plant MTs, but two possible structures have been proposed: 1) a bidominial structure similar to that of vertebrate MTs; 2) a codominial structure, in which two Cys-rich domains interact to form a single metallic cluster. Quaternary structure has not been broadly considered for MTs.
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Sources: en.wikipedia.org
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=== Environment === Viral proteins, engulfed molecules, or degraded self-structures may initiate autoimmunity via molecular mimicry. This may increase the chances of developing Sjögren's disease. Epstein–Barr virus, hepatitis C, and human T-cell leukemia virus-1 are among the most studied infectious agents in Sjögren's disease. To date, no direct cause-and-effect relationship has been identified between these pathogens and the development of Sjögren's disease. Damaged self-structures targeted for apoptosis may be mistakenly exposed to the immune system, triggering autoimmunity in exocrine glands, which are often prone to autoimmune responses.
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== Regulation == H2S decreases transcription of cystathionase at concentrations between 10 and 80 μM. However, transcription is increased by concentrations near 120 μM, and inhibited completely at concentrations in excess of 160 μM.
Sources: en.wikipedia.org
=== Peptides with similar functions === In 2001, biologically active hydroxyproline-rich glycopeptides were isolated from tobacco which activated the production of protease inhibitors in a similar way to systemin in tomatoes. Although they are structurally unrelated to systemins, their similar function resulted in them being named hydroxyproline-rich systemins (HypSys). Following the initial discovery other HypSys peptides were found in tomato, Petunia and black nightshade. In 2007, HypSys were found outside the Solanaceae, in sweet potato (Ipomoea batatas) and sequence analysis identified HypSys analogs in poplar (Populus trichocarpa) and coffee (Coffea canephora). Systemins are highly conserved between species, whereas HypSys are more divergent but all contain a conserved proline or hydroxyproline-rich central domain. In 2006, AtPEP1, a 23 amino acid polypeptide was isolated from Arabidopsis thaliana, which was found to activate components of the innate immune response. Unlike HypSys, AtPEP1 is not post-translationally modified by hydroxylation or glycosylation. Six paralogs of the precursor have been identified in A. thaliana as well as orthologs in grape, rice, maize, wheat, barley, canola, soybean, medicago and poplar, although the activity of these orthologs has not been tested in assays. The predicted structures of the paralogs of AtPEP1 are varied within A. thaliana but all contain a SSGR/KxGxxN sequence motif. The orthologs identified in other species are more varied but still contain components of the sequence motif.
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Kainite, KMg(SO4)·Cl·3H2O Schönite (now known as picromerite), K2SO4·MgSO4·6H2O Leonite, K2SO4·MgSO4·4H2O Langbeinite, K2Mg2(SO4)3 Aphthitalite (previously known as glaserite), K3Na(SO4)2 Polyhalite, K2SO4·MgSO4·2CaSO4·2H2O The potassium sulfate can be separated from some of these minerals, like kainite, because the corresponding salt is less soluble in water. Kieserite, MgSO4·H2O, can be combined with a solution of potassium chloride to produce potassium sulfate.
Sources: en.wikipedia.org
No regulator in a major market has approved it for human use. It appears in research settings and in products marketed outside pharmacy channels. Legal status for personal possession varies by country.
Afamelanotide is a linear analog that has received approval in some jurisdictions for a specific photoprotection indication. Melanotan II is cyclic and less selective across melanocortin receptors. The two are related but are not interchangeable in regulatory or clinical terms.
A compound that activates several receptor subtypes may produce effects beyond pigmentation. Selectivity influences which tissues respond and shapes the side-effect profile described in reports. Designing subtype-selective analogs is a stated goal of melanocortin research.
It is a synthetic seven-amino-acid peptide modeled on alpha-melanocyte-stimulating hormone. It carries two non-natural substitutions and a cyclic bridge that increase its stability relative to the natural hormone. It circulates as a research chemical and is not an approved medicine.