If you have been reading about melanocortin receptor and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-04-11. Numbers and descriptions here follow the published literature rather than marketing material.
Melanotan II is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous peptide involved in pigment production. The analogue carries a lactam bridge that constrains the ring and slows enzymatic breakdown relative to the native hormone. In research literature it appears under several abbreviations, and naming conventions are not fully standardized. Published descriptions usually place it within the broader melanocortin agonist family.
Receptor binding at MC1R on melanocytes raises intracellular cyclic AMP and increases expression of tyrosinase and related enzymes. The downstream result is greater synthesis of eumelanin, the dark pigment, without ultraviolet exposure acting as the trigger. The compound is not selective, however, and also engages MC3R, MC4R and MC5R, which are expressed in the central nervous system and elsewhere. That lack of selectivity is the explanation usually offered for effects reported outside pigmentation, including appetite suppression and nausea. Selectivity remains a central theme in comparative studies of related peptides.
Human data remain limited and mostly short-term. Reports describe small trials and observational accounts rather than large controlled studies, so questions about dose-response relationships and long-term effects on melanocytes stay open. Whether repeated exposure alters naevus behaviour is not settled in the published record. Researchers also note that self-administered use outside clinical settings makes actual exposure difficult to quantify. Statements about efficacy and safety should therefore be read as preliminary rather than established.
Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, corresponding to a molecular formula of C50H69N15O9 and a monoisotopic mass near 1024 daltons. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, a peptide hormone produced by cleavage of proopiomelanocortin. A lactam bridge between the aspartate and lysine side chains closes the ring, and the C-terminal amide removes a free carboxyl group. Both modifications increase resistance to enzymatic degradation compared with the linear parent hormone. Four substitutions distinguish it from afamelanotide, the linear analogue studied under the name melanotan I.
Receptor-binding studies classify melanotan II as a non-selective melanocortin agonist. It interacts with MC1R, MC3R, MC4R and MC5R, with reported affinities in the low nanomolar range and no strong subtype preference. Activation of MC1R on dermal melanocytes shifts pigment synthesis toward eumelanin, the dark polymer deposited in melanosomes and transferred to keratinocytes. Because the same peptide engages MC4R in the hypothalamus, it also appears in animal work on food intake and erectile response, which is why it is discussed in both pigment and metabolic research. Which receptor populations dominate after systemic exposure in humans is not fully established.
Published pharmacokinetic information is limited and comes mainly from small studies rather than registrational trials. Plasma half-life is usually described as short, on the order of tens of minutes, followed by rapid tissue distribution and clearance of the intact peptide. Metabolites and low concentrations of parent compound have been reported in urine, a detail relevant to anti-doping and forensic testing. Whether repeated exposure changes receptor sensitivity or clearance over time remains an open question. Values differ noticeably between analytical assays, so published numbers should be read as approximate rather than definitive.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Melanocortin receptor agonist |
| Molecular formula | C50H69N15O9 | Neutral form, mass near 1024.2 g/mol |
| Primary targets | MC1R, MC3R, MC4R, MC5R | Binding is non-selective across subtypes |
| Related compounds | Alpha-MSH, melanotan I, afamelanotide | Structurally or functionally related peptides |
| Common abbreviations | MT-II, MT-2 | Naming in the literature is not uniform |
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.
Receptor studies place melanotan-2 among non-selective melanocortin agonists, binding MC1R, MC3R, MC4R and MC5R rather than a single subtype. Activation of MC1R on cutaneous melanocytes raises tyrosinase activity and shifts pigment synthesis toward eumelanin, which is darker and more photostable than pheomelanin. Central receptors, particularly MC4R, are associated with appetite suppression and with reported effects on sexual function. Because subtype selectivity is low, the same molecule engages pigment, metabolic and vascular pathways at once, and this breadth is a common explanation offered for the range of adverse events described in user reports.
No regulatory authority has approved melanotan-2 for human use, and several countries classify it as a prescription-only or controlled substance, which restricts lawful supply. Material sold online is generally labelled as a research chemical and is not required to meet pharmaceutical standards of identity or purity. Published human data consist mainly of small uncontrolled studies, case reports and adverse-event notifications, so the evidence base is descriptive rather than confirmatory. Whether repeated melanocyte stimulation alters long-term naevus behaviour remains an open question that no completed trial has resolved.
=== Anti-inflammatory role for sulfoxide === In 1999 researchers in Glasgow University found that an oxidised derivative of thymosin β4 (the sulfoxide, in which an oxygen atom is added to the methionine near the N-terminus) exerted several potentially anti-inflammatory effects on neutrophil leucocytes. It promoted their dispersion from a focus, inhibited their response to a small peptide (F-Met-Leu-Phe) which attracts them to sites of bacterial infection and lowered their adhesion to endothelial cells. (Adhesion to endothelial cells of blood vessel walls is pre-requisite for these cells to leave the bloodstream and invade infected tissue). A possible anti-inflammatory role for the β4 sulfoxide was supported by the group's finding that it counteracted artificially-induced inflammation in mice. The group had first identified the thymosin sulfoxide as an active factor in culture fluid of cells responding to treatment with a steroid hormone, suggesting that its formation might form part of the mechanism by which steroids exert anti-inflammatory effects. Extracellular thymosin β4 would be readily oxidised to the sulfoxide in vivo at sites of inflammation, by the respiratory burst.
Cell death occurs when a cell ceases to carry out its functions, as a result of ageing, or types of cell injury (necrosis). Programmed cell death, including apoptosis, and autophagy is a natural process of replacing dead cells with new ones. A separate mode of cellular death is known as a mitotic catastrophe, which occurs during mitosis, following the improper progression of, or entrance to the cell cycle. This mechanism operates to prevent genomic instability. Other cell death pathways are described, and include anoikis, pyroptosis, mitoptosis, parthanatos, and necroptosis.
sulfur amino acid metabolic processes DNA methylation methionine metabolic processes methionine biosynthetic processes methylation S-adenosylmethionine (SAM) cycle homocysteine catabolic processes folic acid metabolic processes oxidation-reduction processes negative regulation of cystathionine beta-synthase activity.
Sources: en.wikipedia.org
=== Non-inhibitory roles === Non-inhibitory extracellular serpins also perform a wide array of important roles. Thyroxine-binding globulin and transcortin transport the hormones thyroxine and cortisol, respectively. The non-inhibitory serpin ovalbumin is the most abundant protein in egg white. Its exact function is unknown, but it is thought to be a storage protein for the developing foetus. Heat shock serpin 47 is a chaperone, essential for proper folding of collagen. It acts by stabilising collagen's triple helix whilst it is being processed in the endoplasmic reticulum. Some serpins are both protease inhibitors and perform additional roles. For example, the nuclear cysteine protease inhibitor MENT, in birds also acts as a chromatin remodelling molecule in a bird's red blood cells.
(R)-3,4-Methylenedioxy-N-methylamphetamine ([R]-MDMA), also known as (R)-midomafetamine or as levo-MDMA, is the (R)- or levorotatory (l-) enantiomer of 3,4-methylenedioxy-N-methylamphetamine (MDMA; midomafetamine; "ecstasy"), a racemic mixture of (R)-MDMA and (S)-MDMA. Like MDMA, (R)-MDMA is an entactogen or empathogen. It is taken by mouth. The drug is a serotonin–norepinephrine releasing agent (SNRA) and weak serotonin 5-HT2A receptor agonist. It has substantially less or no significant dopamine-releasing activity compared to MDMA and (S)-MDMA. In preclinial studies, (R)-MDMA shows equivalent therapeutic-like effects to MDMA, such as increased prosocial behavior, but shows reduced psychostimulant-like effects, addictive potential, and serotonergic neurotoxicity. In clinical studies, (R)-MDMA produces similar effects to MDMA and (S)-MDMA, but is less potent and has a longer duration. (R)-MDMA was first described in enantiopure form by 1978. Under the developmental code names EMP-01, developed by AtaiBeckley, and DT402 (formerly MM402), developed by Definium Therapeutics (formerly MindMed), it is under development for the treatment of post-traumatic stress disorder (PTSD), social phobia, and pervasive development disorders (PDDs) such as autism. It is thought that (R)-MDMA might have a better safety profile than MDMA itself whilst retaining its therapeutic benefits.
Proteins are often thought of as relatively stable tertiary structures that experience conformational changes after being affected by interactions with other proteins or as a part of enzymatic activity. However, proteins may have varying degrees of stability, and some of the less stable variants are intrinsically disordered proteins. These proteins exist and function in a relatively 'disordered' state lacking a stable tertiary structure. As a result, they are difficult to describe by a single fixed tertiary structure. Conformational ensembles have been devised as a way to provide a more accurate and 'dynamic' representation of the conformational state of intrinsically disordered proteins. Protein ensemble files are a representation of a protein that can be considered to have a flexible structure. Creating these files requires determining which of the various theoretically possible protein conformations actually exist. One approach is to apply computational algorithms to the protein data in order to try to determine the most likely set of conformations for an ensemble file. There are multiple methods for preparing data for the Protein Ensemble Database that fall into two general methodologies – pool and molecular dynamics (MD) approaches (diagrammed in the figure). The pool based approach uses the protein's amino acid sequence to create a massive pool of random conformations. This pool is then subjected to more computational processing that creates a set of theoretical parameters for each conformation based on the structure.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide and a non-selective melanocortin receptor agonist. Structurally it is modelled on alpha-melanocyte-stimulating hormone, a peptide that occurs naturally in the body.
Activation of MC1R increases pigment synthesis independently of ultraviolet exposure, which is the mechanism usually cited for darkening without sun exposure. Ultraviolet light still influences skin response through separate biological pathways.
Because the peptide binds several melanocortin receptor subtypes, its effects are not confined to pigmentation. This complicates interpretation of both intended and unintended outcomes reported in studies.
No. It is a synthetic analogue carrying four amino acid changes, a lactam ring and an amidated C-terminus. The natural hormone is a linear thirteen-amino-acid peptide processed from proopiomelanocortin.