melanocortin receptor is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-06-04. Numbers and descriptions here follow the published literature rather than marketing material.
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controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports.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.
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
Early published reports described melanotan-2 as a tanning agent without sun protection, which means darkening is not the same as protection against ultraviolet radiation. Later studies explored the peptide in erectile dysfunction, hemorrhagic shock, and some skin conditions. No regulator in the United States or Europe has approved it for clinical use. Many products labelled melanotan-2 are sold without approval and their identity and purity are unverified. Its long-term safety in humans remains an open question.
Melanotan-2, also written Melanotan II, is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and the lactam bridge between the aspartate and lysine side chains constrains the peptide into a ring. This structural change increases receptor affinity and metabolic stability relative to the native hormone. The compound was created in the 1980s as a research tool for studying pigmentation biology.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Alpha-MSH analogue with a lactam ring |
| Molecular formula | C50H69N15O9 | Commonly cited value for the neutral peptide |
| Molecular weight | 1024.18 g/mol | Calculated for the free molecule |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water, DMSO and ethanol | Dissolution in pure water is often slow |
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.
Melanocortin receptors comprise five subtypes with distinct tissue distributions and functions. Melanotan-2 is described in the literature as a non-selective agonist that engages several of these subtypes, including MC1R, MC3R, MC4R, and MC5R. MC1R is the subtype most directly linked to melanin production in skin cells. Because the compound is not subtype-selective, its observed effects in experimental settings are generally attributed to activity across multiple receptor pathways rather than to a single target.
Melanotan-2 is a synthetic linear peptide built from seven amino acids arranged in a short chain. Its sequence is commonly written as Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-NH2, which includes a modified N-terminus and an amidated C-terminus. The molecule belongs to the melanocortin family and acts as a receptor agonist. Structural features such as the D-phenylalanine residue and the Nle substitution are associated with increased stability against enzymatic degradation relative to the natural parent peptide.
A case of major potassium depletion has been attributed to chronic licorice ingestion, and consequently professional herbalists avoid the use of licorice where they recognize that this may be a risk. Black cohosh has been implicated in a case of liver failure. Few studies are available on the safety of herbs for pregnant women, and one study found that use of complementary and alternative medicines is associated with a 30% lower ongoing pregnancy and live birth rate during fertility treatment. Examples of herbal treatments with likely cause-effect relationships with adverse events include aconite (which is often a legally restricted herb), Ayurvedic remedies, broom, chaparral, Chinese herb mixtures, comfrey, herbs containing certain flavonoids, germander, guar gum, liquorice root, and pennyroyal. Examples of herbs that may have long-term adverse effects include ginseng, the endangered herb goldenseal, milk thistle, senna, aloe vera juice, buckthorn bark and berry, cascara sagrada bark, saw palmetto, valerian, kava (which is banned in the European Union), St. John's wort, khat, betel nut, the restricted herb ephedra, and guarana. There is also concern with respect to the numerous well-established interactions of herbs and drugs.
== Structure == In bacteria, HDH is a single chain polypeptide; in fungi it is the C-terminal domain of a multifunctional enzyme which catalyses three different steps of histidine biosynthesis; and in plants it is expressed as a nuclear encoded protein precursor which is exported to the chloroplast.
Nuclear export of SENP2 additionally downregulates endothelial nitric oxide synthase, eNOS while it upregulates inflammatory adhesion molecules. As eNOS is required for healthy vascular physiology, pathological oxidative stress ensues in vascular endothelial cells. With the oxidative stress comes subsequent accumulation of cellular lipids; this results in the inflammatory foamy cell state that is typified by atherosclerosis as well as the similarly inflammatory myelin-laden macrophages known to produce chronic inflammation in SCI. In cardiovascular disease, many proteins are subject to SUMOylation. To say SUMOylation itself is bad or good regarding this or any other class of disease is to overlook the role of the multiple proteins in question. One common denominator among many conditions is fibrosis; in myocardial fibrosis, PPARγ1 is understood to have a role in regulating expression of some key genes, and its transcriptional activity is generally inhibited by SUMOylation. Therefore, one possible therapeutic intervention in the case of cardiac hypertrophy may be countering the SUMOylation of PPARγ1. In neurodegenerative disease, we often observe pathological accumulation of proteins. Inclusion bodies form when for example, the Huntington's disease protein, aptly named Huntingtin, accumulates and folds into a form which is impervious to the proteasome.
=== brGDGT === The building blocks of brGDGT, specifically the long alkyl groups (iso-diabolic acid), are detected in acidobacteria subdivisions 1, 3, 4, and 6. Small amounts of brGDGT-I was detected in Acidobacteriaceae strain A2-4c by full mass spectrum and tentatively in Acidobacteriaceae strain 307 by single-ion monitoring MS; none has been detected in the 44 other strains tested as of 2018. More complex brGDGTs known from nature have not yet been detected in any cell culture.
Sources: en.wikipedia.org
There were other witnesses for the defense who did not show up. Several scientists who had been listed as potential witnesses for the state, backed out because of what Clark termed "peer pressure." Another state witness, Dr. Dean Kenyon, a biophysicist at San Francisco State University, mysteriously disappeared on the eve of his day in court. He had flown into Little Rock on a Sunday evening, but when one of Clark's assistants went to take his deposition he could not find him. Kenyon had checked out of the hotel and flown back home. Bird had encouraged Kenyon not to testify, although Kenyon taught evolution theory for 16 years until three years ago when he became a creationist. Bird, who is general counsel to Institute for Creation Research, said he attempted to get other defense witnesses not to testify after he perceived the trial as botched by Clark.
Calcium acetate - their coordination complexes Poly(alkyl methacrylate) - especially poly(isobutyl methacrylate) Polystyrene Aluminum oxide - (some grades) Paraffin wax Aluminum alcoholate (ISO-series) Silicon dioxide (some grades) Natural rubber (LA-series) tetraoxyborate - their coordination complexes Casein Sulfur (polysulfides) Polybutadiene Asphalt - and other organic minerals Bentonite clay (lyophilic type) Colloidal metal Metallic soaps - especially hydroxyaluminum soaps Cellulose derivatives Metal alkyls - especially dialkyl hydroxygallium and trialkyltin fluorides Carbomer Alginate
=== Pharmacogenetics === Since doxepin is mainly metabolized by CYP2D6, CYP2C9, and CYP2C19, genetic variations within the genes coding for these enzymes can affect its metabolism, leading to changes in the concentrations of the drug in the body. Increased concentrations of doxepin may increase the risk for side effects, including anticholinergic and nervous system adverse effects, while decreased concentrations may reduce the drug's efficacy. Individuals can be categorized into different types of cytochrome P450 metabolizers depending on which genetic variations they carry. These metabolizer types include poor, intermediate, extensive, and ultrarapid metabolizers. Most people are extensive metabolizers, and have "normal" metabolism of doxepin. Poor and intermediate metabolizers have reduced metabolism of the drug as compared to extensive metabolizers; patients with these metabolizer types may have an increased probability of experiencing side effects. Ultrarapid metabolizers break down doxepin much faster than extensive metabolizers; patients with this metabolizer type may have a greater chance of experiencing pharmacological failure. A study assessed the metabolism of a single 75 mg oral dose of doxepin in healthy volunteers with genetic polymorphisms in CYP2D6, CYP2C9, and CYP2C19 enzymes. In CYP2D6 extensive, intermediate, and poor metabolizers, the mean clearance rates of (E)-doxepin were 406, 247, and 127 L/hour, respectively (~3-fold difference between extensive and poor).
The lowest temperatures on record in most cities in the eastern United States were set after a mass of cold air came south from Canada. Record lows ranged from International Falls, Minnesota −45 °F (−43 °C) to Washington, D.C. and Jackson, Mississippi−5 °F (−21 °C), and were set in Milwaukee −26 °F (−32 °C), Pittsburgh −18 °F (−28 °C) and Cleveland −17 °F (−27 °C) Winston Cenac resigned as Prime Minister of Saint Lucia after 8 months in office, and was succeeded temporarily by Finance Minister Michael Pilgrim. Born: Dwyane Wade, American NBA player and team owner, 2006 MVP of the NBA Finals for the Miami Heat, inductee to the Basketball Hall of Fame, and later a minority owner of the Utah Jazz and the WNBA Chicago Sky; in Chicago Died: Varlam Shalamov, Russian writer known for Kalyma's Notes, an exposure of the horrors of Soviet labor camps, where he had been incarcerated from 1937 to 1954 Jusuf Gërvalla, 38, Albanian-born Yugoslavian Kosovo independence activist and founder of a Yugoslavian separatist group, the National Movement for the Liberation of Kosovo, was shot to death in West Germany by Yugoslavia's State Security Service. He, his brother Bardhosh Gërvalla, and another activist, Kadri Zeka, were sitting in a car in the town of Untergruppenbach when all three were killed. William Price, 86, British World War One flying ace with seven shootdowns Pierre De Cazenove De Pradines, 87, French flying ace in World War One with seven aerial victories.
Thrombocytopenia, typically multifactorial, is due to alcoholic marrow suppression, sepsis, lack of folate, platelet sequestering in the spleen, and decreased thrombopoietin. However, this rarely results in a platelet count < 50,000/mL. Aminotransferases AST and ALT are moderately elevated, with AST > ALT. However, normal aminotransferase levels do not preclude cirrhosis. Alkaline phosphatase – slightly elevated but less than 2–3 times the upper limit of normal. Gamma-glutamyl transferase – correlates with AP levels. Typically, much higher in chronic liver disease from alcohol. Bilirubin levels are normal when compensated, but may elevate as cirrhosis progresses. Albumin levels fall as the synthetic function of the liver declines with worsening cirrhosis, since albumin is exclusively synthesized in the liver. Prothrombin time increases, since the liver synthesizes clotting factors. Globulins increase due to shunting of bacterial antigens away from the liver to lymphoid tissue. Serum sodium levels fall (hyponatremia) due to inability to excrete free water resulting from high levels of ADH and aldosterone. Leukopenia and neutropenia are due to splenomegaly with splenic margination. Coagulation defects occur, as the liver produces most of the coagulation factors; thus, coagulopathy correlates with worsening liver disease. Glucagon is increased in cirrhosis. Vasoactive intestinal peptide is increased as blood is shunted into the intestinal system because of portal hypertension.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide modelled on alpha-melanocyte-stimulating hormone. A lactam bridge links two side chains, forming a ring that stabilises the molecule against proteolysis. It belongs to the broader melanocortin peptide family.
No national medicines agency has approved melanotan-2 for clinical use. Afamelanotide, a related but distinct peptide, holds a marketing authorisation in the European Union for a rare photosensitivity disorder. Melanotan-2 itself is handled as a laboratory chemical.
Its broad activity across melanocortin receptors makes it a tool for probing pigmentation, appetite and vascular signalling. Early trials recorded skin darkening and other effects that were not the original focus of the work. Those observations generated hypotheses that later studies have examined.
No. It is a laboratory-made peptide, while the natural hormone is alpha-melanocyte-stimulating hormone, a longer peptide produced by the pituitary gland and by skin cells. Melanotan-2 mimics only a short active region of that hormone and contains non-natural residues such as D-phenylalanine.