The short version of melanocortin receptors fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
The compound was developed in the late 1980s and 1990s by academic researchers investigating photoprotection. The rationale held that stimulating melanin production might reduce ultraviolet damage to skin and lower skin cancer risk. Early work examined receptor binding, pigment response, and short-term tolerability in small studies. That program did not produce an approved drug, and formal development stalled after early-phase trials. Whether induced pigmentation confers meaningful photoprotection remains an open question.
Outside regulated medicine, melanotan II circulates through online vendors as a research chemical, often marketed for tanning. Products sold this way vary widely in purity, concentration, and labeling accuracy, and independent testing has documented discrepancies. Published reports describe both pigment effects and adverse reactions, including nausea, flushing, and darkening of existing moles. Long-term safety data are sparse, and no large controlled trial has established a risk profile. Questions about cumulative effects on melanocytes remain unresolved in the literature.
Melanotan II is a synthetic peptide analog modeled on alpha-melanocyte-stimulating hormone, a naturally occurring signaling peptide involved in pigmentation. Its structure is a cyclic heptapeptide containing two non-natural substitutions, norleucine at position four and D-phenylalanine at position seven. These modifications resist enzymatic breakdown and extend the molecule's activity relative to the native hormone. The compound binds melanocortin receptors and is studied mainly as a pharmacological tool rather than a therapeutic product. It has never received approval as a medicine in any major jurisdiction.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Belongs to the melanocortin agonist family |
| Key substitutions | Nle4 and D-Phe7 | Improve resistance to enzymatic degradation |
| Molecular formula | C50H69N15O9 | Approximately 1024 g/mol |
| Regulatory status | Not approved as a medicine | Distributed as a research chemical |
| Common synonyms | Melanotan II, MT-II, MT-2 | Spelling varies across sources |
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, the naturally occurring peptide involved in pigmentation signalling. Its sequence is conventionally written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, with a lactam bridge joining the aspartate side chain to the lysine side chain. The empirical formula is C50H69N15O9 and the monoisotopic mass lies near 1023.5 daltons. N-terminal acetylation and the D-configured phenylalanine both increase resistance to enzymatic breakdown compared with the parent hormone.
Pharmacologically, melanotan-2 behaves as a non-selective agonist across the melanocortin receptor family. Binding at MC1R on dermal melanocytes promotes eumelanin synthesis, which underlies the tanning response described in early human work. Activity at the centrally expressed MC4R receptor is associated with reported effects on appetite and erectile function. Because the peptide does not discriminate strongly among receptor subtypes, attributing any single observed effect to one receptor pathway is generally not possible without selective antagonists or receptor knockout models.
Research interest has centred on photoprotection and pigmentation, with a smaller body of work on appetite and sexual function. Published human data remain limited to small, frequently uncontrolled studies, and the compound has never received marketing approval from a national medicines regulator. Most laboratory work treats it as a pharmacological tool for probing melanocortin signalling in cell culture or animal models. Whether pigmentation changes observed in people translate into measurable protection against ultraviolet-induced DNA damage remains an open question.
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.
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.
It is the most common cause of infections of burn injuries and of the outer ear (otitis externa) and is the most frequent colonizer of medical devices (e.g. catheters). Pseudomonas can be spread by equipment that becomes contaminated and is not properly cleaned or on the hands of healthcare workers. Pseudomonas can, in rare circumstances, cause community-acquired pneumonias, as well as ventilator-associated pneumonias, being one of the most common agents isolated in several studies. Pyocyanin is a virulence factor of the bacteria and has been known to cause death in C. elegans by oxidative stress. However, salicylic acid can inhibit pyocyanin production. One in ten hospital-acquired infections is from Pseudomonas . Cystic fibrosis patients are also predisposed to P. aeruginosa infection of the lungs due to a functional loss in chloride ion movement across cell membranes as a result of a mutation. P. aeruginosa may also be a common cause of "hot-tub rash" (dermatitis), caused by lack of proper, periodic attention to water quality. Since these bacteria thrive in moist environments, such as hot tubs and swimming pools, they can cause skin rash or swimmer's ear. Pseudomonas is also a common cause of postoperative infection in radial keratotomy surgery patients. The organism is also associated with the skin lesion ecthyma gangrenosum. P. aeruginosa is frequently associated with osteomyelitis involving puncture wounds of the foot, believed to result from direct inoculation with P. aeruginosa via the foam padding found in tennis shoes, with diabetic patients at a higher risk.
Dissociation of the target mRNA strand from RISC after the cleavage allows more mRNA to be silenced; this dissociation process is likely to be promoted by extrinsic factors driven by ATP hydrolysis. Sometimes, cleavage of the target mRNA molecule does not occur. In some cases, the endonucleolytic cleavage of the phosphodiester backbone may be suppressed by mismatches of siRNA and target mRNA near the cleaving site. Other times, the Argonaute proteins of the RISC lack endonuclease activity even when the target mRNA and siRNA are perfectly paired. In such cases, gene expression will be silenced by an miRNA-induced mechanism instead.
== External links == Parathyroid+Hormone+Receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH) "Parathyroid Hormone Receptors". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.
Sources: en.wikipedia.org
=== Sequencing insulin === Neuberger moved to the National Institute for Medical Research in London, but Sanger stayed in Cambridge and in 1943 joined the group of Charles Chibnall, a protein chemist who had recently taken up the chair in the Department of Biochemistry. Chibnall had already done some work on the amino acid composition of bovine insulin and suggested that Sanger look at the amino groups in the protein. Insulin could be purchased from the pharmacy chain Boots and was one of the very few proteins that were available in a pure form. Up to this time Sanger had been funding himself. In Chibnall's group he was initially supported by the Medical Research Council and then from 1944 until 1951 by a Beit Memorial Fellowship for Medical Research. Sanger's first triumph was to determine the complete amino acid sequence of the two polypeptide chains of bovine insulin, A and B, in 1952 and 1951, respectively. Prior to this it was widely assumed that proteins were somewhat amorphous. In determining these sequences, Sanger proved that proteins have a defined chemical composition. To get to this point, Sanger refined a partition chromatography method first developed by Richard Laurence Millington Synge and Archer John Porter Martin to determine the composition of amino acids in wool. Sanger used a chemical reagent 1-fluoro-2,4-dinitrobenzene (now, also known as Sanger's reagent, fluorodinitrobenzene, FDNB or DNFB), sourced from poisonous gas research by Bernard Charles Saunders at the Chemistry Department at Cambridge University.
==== Autoimmune diseases ==== Monoclonal antibodies used for autoimmune diseases include infliximab and adalimumab, which are effective in rheumatoid arthritis, Crohn's disease, ulcerative colitis and ankylosing spondylitis by their ability to bind to and inhibit TNF-α. Basiliximab and daclizumab inhibit IL-2 on activated T cells and thereby help prevent acute rejection of kidney transplants. Omalizumab inhibits human immunoglobulin E (IgE) and is useful in treating moderate-to-severe allergic asthma.
The concentration of secondary metabolites such as phenylpropanoids and flavonoids can also be altered in plants exposed to high concentrations of CO2. Plants also emit CO2 during respiration, and so the majority of plants and algae, which use C3 photosynthesis, are only net absorbers during the day. Though a growing forest will absorb many tons of CO2 each year, a mature forest will produce as much CO2 from respiration and decomposition of dead specimens (e.g., fallen branches) as is used in photosynthesis in growing plants. Contrary to the long-standing view that they are carbon neutral, mature forests can continue to accumulate carbon and remain valuable carbon sinks, helping to maintain the carbon balance of Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO2 in the upper ocean and thereby promotes the absorption of CO2 from the atmosphere.
Sources: en.wikipedia.org
It is a synthetic cyclic peptide designed as an analog of alpha-melanocyte-stimulating hormone. It acts on melanocortin receptors and is best known from research into pigmentation. It is not an approved pharmaceutical product.
No regulatory agency has approved it for any indication. It is encountered as a research chemical sold outside pharmaceutical supply chains. Products marketed this way are not subject to the manufacturing and labeling requirements that apply to approved drugs.
Reports describe increased skin pigmentation as well as side effects such as nausea, flushing, and changes to existing moles. Much of the evidence comes from small studies and case reports rather than large trials. The long-term safety profile is therefore uncertain.
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.