The short version of melanocortin receptor fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-09-05. Anything still debated is marked as such rather than presented as settled.
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.
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.
| 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 |
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 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.
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.
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.
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.
=== Simulated chemical pathways === In 2020, chemists described possible chemical pathways from nonliving prebiotic chemicals to complex biochemicals that could give rise to living organisms, based on a new computer program named AllChemy.
This cylindrical representation of the incompressible Navier–Stokes equations is the second most commonly seen (the first being Cartesian above). Cylindrical coordinates are chosen to take advantage of symmetry, so that a velocity component can disappear. A very common case is axisymmetric flow with the assumption of no tangential velocity (
Israel: Gideon Sa'ar, the Minister of Foreign Affairs, stated via X that "Israel commends the United States' operation, led by President Trump, which acted as the leader of the free world. At this historic moment, Israel stands alongside the freedom-loving Venezuelan people, who have suffered under Maduro's illegal tyranny. Israel welcomes the removal of the dictator who led a network of drugs and terror and hopes for the return of democracy to the country and for friendly relations between the states. The people of Venezuela deserve to exercise their democratic rights. South America deserves a future free from the axis of terror and drugs." Prime Minister Benjamin Netanyahu stated that Israel supported the U.S. "strong action" in Venezuela. Japan: Prime Minister Sanae Takaichi tweeted that the "Japanese government is responding to this situation in close cooperation with relevant countries", stating that she is prioritizing the safety of Japanese nationals in Venezuela and "will also advance diplomatic efforts towards the restoration of democracy and stabilization of the situation in Venezuela". The Ministry of Foreign Affairs responded to the US strikes and intervention by reiterating its position as a G7 country, and offering support "toward the restoration of democracy and the stabilisation of the situation in Venezuela". North Korea: A Ministry of Foreign Affairs spokesperson responded to a query about the U.S.
In natural history museums, researchers and curators sometimes wish to study or display animal skeletons. In the Natural History Museum in London, the American Museum of Natural History in New York, and the Australian National Wildlife Collection in Canberra, dermestid beetles are used for skeleton preparation. Dermestid beetles eat hair, skin and flesh, but not bones, and are considered an excellent way of creating clean, professional-grade bone specimens.
== Composition == The prepreg matrix consists of a mixture of resin and hardener, in some cases an accelerator. Freezing at -20 °C prevents the resin from reacting with the hardener. If the cold chain is interrupted, the reaction starts and the prepreg becomes unusable. There are also high-temperature prepregs which can be stored for a certain time at room temperature. These prepregs can then be cured only in an autoclave at elevated temperature.
Sources: en.wikipedia.org
Some sources consider these movies to be part of Season 1 of the series, particularly the second and third films, which aired only a couple of months before the weekly series began. All three films were later re-edited into two-part episodes of the regular series, with additional footage added, for the purposes of network reruns and later syndication. In all three cases, the original opening titles are removed and replaced with the standard Six Million Dollar Man title sequence. In the case of "The Moon and the Desert", some of the additional footage consisted of clips from later seasons, including footage of Martin E. Brooks as Rudy Wells, even though Martin Balsam plays the character in the first telefilm, and operation footage from "The Bionic Woman" episode of season 2.
An academic discipline or academic field is a subdivision of knowledge that is taught and researched at the college or university level. Disciplines are defined (in part) and recognized by the academic journals in which research is published, and the learned societies and academic departments or faculties within colleges and universities to which their practitioners belong. Academic disciplines are conventionally divided into the humanities (including philosophy, languages, art and cultural studies), the natural sciences (such as physics, chemistry, and biology); and the formal sciences like mathematics and computer science. The social sciences are sometimes considered a fourth category. It is also known as a field of study, field of inquiry, research field and branch of knowledge. The different terms are used in different countries and fields. Individuals associated with academic disciplines are commonly referred to as experts or specialists. Others, who may have studied liberal arts or systems theory rather than concentrating in a specific academic discipline, are classified as generalists. The following outline provides an overview of and topical guide to academic disciplines. In each case, an entry at the highest level of the hierarchy (e.g., Humanities) is a group of broadly similar disciplines; an entry at the next highest level (e.g., Music) is a discipline having some degree of autonomy and being the fundamental identity felt by its scholars.
=== Design for affinity === Protein–protein interactions are involved in most biotic processes. Many of the hardest-to-treat diseases, such as Alzheimer's disease, many forms of cancer (e.g., TP53), and human immunodeficiency virus (HIV) infection involve protein–protein interactions. Thus, to treat such diseases, it is desirable to design protein or protein-like therapeutics that bind one of the partners of the interaction and, thus, disrupt the disease-causing interaction. This requires designing protein-therapeutics for affinity toward its partner. Protein–protein interactions can be designed using protein design algorithms because the principles that rule protein stability also rule protein–protein binding. Protein–protein interaction design, however, presents challenges not commonly present in protein design. One of the most important challenges is that, in general, the interfaces between proteins are more polar than protein cores, and binding involves a tradeoff between desolvation and hydrogen bond formation. To overcome this challenge, Bruce Tidor and coworkers developed a method to improve the affinity of antibodies by focusing on electrostatic contributions. They found that, for the antibodies designed in the study, reducing the desolvation costs of the residues in the interface increased the affinity of the binding pair.
=== Retinoblastoma === More recent studies have identified ITGA1 as a potential therapeutic target in retinoblastoma (Rb). ITGA1 promotes Rb progression by activating the FAK/STAT3 signaling pathway. Restoration of STAT3 partially reverses the effects of ITGA1 inhibition, supporting the role of this pathway in ITGA1-mediated tumor growth. Genetic knockdown or pharmacological inhibition of ITGA1 suppresses retinoblastoma cell proliferation, migration, colony formation, and growth in vivo. Inhibition of the α1β1 integrin receptor using genetic approaches or the α1β1 inhibitor obtustatin reduces tumor progression, suggesting that ITGA1-targeted therapies may represent a potential strategy for treating high-risk retinobloastoma. However, further research and testing are needed to confirm the safety and efficacy of ITGA1 inhibition before it is used as a clinical treatment.
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.
No. Melanotan-2 is manufactured synthetically. The naturally occurring peptide in the same family is alpha-melanocyte-stimulating hormone, which the body produces as part of normal endocrine and neural signalling.