This is a working overview of melanocortin receptors, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-09-14 and is reviewed periodically as new material appears.
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.
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.
Regulatory treatment varies by country. In the United States, melanotan-2 is not approved for any indication, and products marketed for human use fall outside the approved drug framework. Some other jurisdictions have placed it under prescription controls or listed it as a prohibited or restricted substance. Online listings frequently describe the material as a research chemical, a category that does not carry the same manufacturing and labelling requirements as approved medicines.
Solid peptide material is generally stable when kept cold and dry. Common practice is storage at -20 degrees Celsius or lower, with desiccant and protection from light. Repeated freeze-thaw cycles and exposure to moisture are associated with degradation, aggregation, or loss of material. Once dissolved, stability depends on solvent, concentration, and temperature, and solutions are usually treated as short-lived unless stability data support longer periods. Handling notes typically emphasise minimising time at ambient temperature.
Identity and purity are assessed with chromatographic and mass spectrometric techniques. Reversed-phase high-performance liquid chromatography separates the target peptide from related impurities and degradation products, and the resulting retention time is compared against a reference standard. Mass spectrometry, often coupled to liquid chromatography, confirms molecular mass. Amino acid analysis or peptide mapping can provide additional sequence-level confirmation when required. Results are only as reliable as the reference materials used alongside them.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Cyclic heptapeptide, C-terminally amidated |
| Approximate molecular mass | 1024 Da | Monoisotopic mass of the free peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility class | Soluble in water and polar solvents | Also dissolves in neutral aqueous buffer |
| Common synonyms | Melanotan II, MT-II, MT-2 | Described as a melanocortin agonist in early literature |
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.
Structurally, Melanotan-2 retains the core recognition motif of alpha-melanocyte-stimulating hormone while adding a lactam bridge that links two side chains and constrains the molecule into a ring. This modification lowers susceptibility to enzymatic degradation. The compound acts as an agonist at melanocortin receptors, particularly subtypes associated with melanin production. Because the same receptor family influences several physiological processes, researchers note that its activity is not confined to pigmentation alone. Receptor selectivity continues to be examined in published studies.
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.
Melanotan-2 appears on the World Anti-Doping Agency prohibited list within the peptide hormone class, and several national regulators treat it as an unapproved prescription substance. Some countries restrict importation or sale for personal use. Because the compound is widely traded as a research chemical, the practical legal picture differs between jurisdictions and shifts over time. Human safety data covering long periods are limited, and whether repeated pigmentation changes carry any lasting risk to melanocytes remains an open question.
Freeze-dried melanotan-2 is normally kept as a desiccated powder at minus twenty degrees Celsius or lower, shielded from light and moisture. Peptides of this size degrade through hydrolysis, oxidation and deamidation, and each pathway accelerates as temperature and water activity rise. Repeated freeze-thaw cycles promote aggregation and loss of material, so aliquoting a stock solution before freezing is standard laboratory practice. Once dissolved, the solution is markedly less stable than the powder. In laboratory work, solutions are generally refrigerated and used within days rather than kept for months.
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-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.
Regulatory treatment varies by country. In the United States the peptide is not approved as a medicine, and products offered for human use may be treated as unapproved new drugs; some states also restrict sale. Australia, the United Kingdom, and European Union member states apply comparable restrictions to unapproved peptide products. Border agencies have seized shipments labelled as research chemicals. Classification may change over time, and the legal position for personal importation is not clearly settled in most published guidance.
Lyophilised melanotan-2 is supplied as a solid, which is more stable than a solution. The material is hygroscopic, so weighing is done quickly, in low humidity, with the container kept sealed. Reconstitution usually uses water for injection or bacteriostatic water, added down the wall of the vial to limit foaming. A reconstituted solution is held at 2 to 8 °C and kept away from light. Repeated freezing and thawing of the same vial is avoided because ice crystal formation and concentration effects degrade the peptide.
Reversed-phase high-performance liquid chromatography is the routine method for purity assessment. Peptides absorb near 214 nm because of the peptide bond, and a gradient of acetonitrile in water separates the intact peptide from deletion sequences, oxidised products, and earlier-eluting fragments at neutral pH. Electrospray ionisation mass spectrometry provides an orthogonal check: the measured mass must agree with the theoretical value. Amino acid analysis and peptide mapping confirm structure but are used less often. Reference standards remain scarce because the peptide is not described in any pharmacopoeia.
The former maintains its own border control policies, thus requiring physical border security at its border with the Schengen Area, as well as implementing border controls for travellers travelling directly between Gibraltar and the British mainland. The latter maintains a relatively open border with Southern Cyprus, though not with Northern Cyprus. Consequently, it is a de facto member of the Schengen Area, and travel to or from the British mainland is subject to border controls. On 31 December 2020, Spain and the United Kingdom reached an agreement in principle under which Gibraltar would join the Schengen Area, clearing the way for the European Union and the UK to start formal negotiations on the matter. In the aftermath of Brexit, border controls for goods flowing between Great Britain and Northern Ireland were introduced in accordance with the Protocol on Ireland/Northern Ireland agreed to as part of the UK's withdrawal agreement with the EU. Due to the thirty-year internecine conflict in Northern Ireland, the UK-Ireland border has had a special status since that conflict was ended by the Belfast Agreement/Good Friday Agreement of 1998. As part of the Northern Ireland Peace Process, the border has been largely invisible, without any physical barrier or custom checks on its many crossing points; this arrangement was made possible by both countries' common membership of both the EU's Single Market and Customs Union and of their Common Travel Area.
opsonin Any substance, especially certain blood-serum proteins such as immunoglobulins, that in binding to the surface of foreign cells or particulate matter increases the susceptibility of the foreign material to phagocytosis by phagocytes. Opsonins work by linking foreign particles to specific receptors on the surface of phagocytic cells in a process known as opsonization.
In August 1914 Britain entered the First World War. Tolkien's relatives were shocked when he elected not to volunteer immediately for the British Army. In a 1941 letter to his son Michael, Tolkien recalled: "In those days chaps joined up, or were scorned publicly. It was a nasty cleft to be in for a young man with too much imagination and little physical courage." Instead, Tolkien, "endured the obloquy", and entered a programme by which he delayed enlistment until completing his degree. By the time he passed his finals in July 1915, Tolkien recalled that the hints were "becoming outspoken from relatives". He was commissioned as a temporary second lieutenant in the Lancashire Fusiliers on 15 July 1915. He trained with the 13th (Reserve) Battalion on Cannock Chase, Rugeley Camp near to Rugeley, Staffordshire, for eleven months. In a letter to Edith, Tolkien complained: "Gentlemen are rare among the superiors, and even human beings rare indeed." Following their wedding Lieutenant and Mrs. Tolkien took up lodgings near the training camp. On 2 June 1916, Tolkien received a telegram summoning him to Folkestone for posting to France. The Tolkiens spent the night before his departure in a room at the Plough & Harrow Hotel in Edgbaston, Birmingham. He later wrote: "Junior officers were being killed off, a dozen a minute. Parting from my wife then ... it was like a death."
Mexico has both public and private universities, with wide variation in terms of cost, academic performance, and organization. The most reputable and largest university, the National Autonomous University of Mexico (UNAM), is publicly funded and virtually free, while also independent from the government. Instituto Politécnico Nacional is a federally-administered public university. Several public state universities follow an autonomous model similar to UNAM, including Universidad de Guadalajara and Universidad Autónoma de Nuevo León. However, these state universities do not receive as much public funding, which means higher tuition fees.
No natural reservoir for SARS-CoV-2 has been identified. Prior to the emergence of SARS-CoV-2 as a pathogen infecting humans, there had been two previous zoonosis-based coronavirus epidemics, those caused by SARS-CoV-1 and MERS-CoV. The first known infections from SARS‑CoV‑2 were discovered in Wuhan, China. The nature of the virus's origins remain unclear and disputed. The original source of viral transmission to humans remains unclear, as does whether the virus became pathogenic before or after the spillover event. Because many of the early infectees were workers at the Huanan Seafood Market, it has been suggested that the virus might have originated from the market. Other research indicates that visitors may have introduced the virus to the market, which then facilitated rapid expansion of the infections. A March 2021 WHO-convened report stated that human spillover via an intermediate animal host was the most likely explanation, with direct spillover from bats next most likely. Introduction through the food supply chain and the Huanan Seafood Market was considered another possible, but less likely, explanation. Later analysis in November 2021 said that the earliest-known case had been misidentified and that the preponderance of early cases linked to the Huanan Market argued for it being the source. For a virus recently acquired through a cross-species transmission, rapid evolution is expected. The mutation rate estimated from early cases of SARS-CoV-2 was of 6.54×10−4 per site per year.
Sources: en.wikipedia.org
First, it exists to exploit the author-pays Open Access model to generate revenue, and second, it serves as an easy place for foreign (chiefly Chinese) authors to publish overseas and increase their academic status." He acknowledges that its fees are relatively low, describing this as "a strategy that increases article submissions," and that "it has attracted some quality article submissions. Nevertheless, it is really a vanity press." Further controversy was generated by a mass resignation of the editorial board of one of the company's journals, Advances in Anthropology, in 2013. According to the former editor-in-chief, Fatimah Jackson, it was motivated by failures to include the editorial board in the journal's review process, and by "consistent and flagrant unethical breaches by the editorial staff in China", for whom publishing the journal "was only about making money." According to Beall, this was the first mass resignation from an open-access journal. In 2021 Cabells' Predatory Reports described SCIRP as a "well-known predatory publisher". In the Norwegian Scientific Index, the publisher and all of its journals have a rating of 0 (non-academic). An academic study published in 2022 stated that SCIRP was "widely known to host 'fake journals'".
the presence of acid (primarily the secreted HCl) that leads to a low pH in the stomach (a case of negative feedback) somatostatin also inhibits the release of gastrin, along with secretin, GIP (gastroinhibitory peptide), VIP (vasoactive intestinal peptide), glucagon and calcitonin.
=== Pharmacokinetics === The absorption of flutamide is complete upon oral ingestion. Food has no effect on the bioavailability of flutamide. Steady-state levels of hydroxyflutamide, the active form of flutamide, are achieved after 2 to 4 days administration. Levels of hydroxyflutamide are approximately 50-fold higher than those of flutamide at steady-state. The plasma protein binding of flutamide and hydroxyflutamide are high; 94 to 96% and 92 to 94%, respectively. Flutamide and its metabolite hydroxyflutamide are known to be transported by the multidrug resistance-associated protein 1 (MRP1; ABCC1). Flutamide is metabolized by CYP1A2 (via α-hydroxylation) in the liver during first-pass metabolism to its main metabolite hydroxyflutamide (which accounts for 23% of an oral dose of flutamide one hour post-ingestion), and to at least five other, minor metabolites. Flutamide has at least 10 inactive metabolites total, including 4-nitro-3-fluoro-methylaniline. Flutamide is excreted in various forms in the urine, the primary form being 2-amino-5-nitro-4-(trifluoromethyl)phenol. Flutamide and hydroxyflutamide have elimination half-lives of 4.7 hours and 6 hours in adults, respectively. However, the half-life of hydroxyflutamide is extended to 8 hours after a single dose and to 9.6 hours at steady state) in elderly individuals. The elimination half-lives of flutamide and hydroxyflutamide are regarded as too short to allow for once-daily dosing, and for this reason, flutamide is instead administered three times daily at 8-hour intervals.
== Origin of the word "Radurisation" == The word "radurisation" is derived from radura, combining the initial letters of the word "radiation" with the stem of "durus", the Latin word for hard, lasting.
Sources: en.wikipedia.org
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.
Afamelanotide is the linear analogue [Nle4-D-Phe7]-alpha-MSH, sometimes called melanotan I, while melanotan II is cyclic and carries three further substitutions. The two are distinct molecules and are not interchangeable in analytical testing.
Binding to the four melanocortin receptor subtypes is well documented in vitro. The relative contribution of each subtype to whole-body effects in humans is far less certain.
Laboratory confirmation typically combines retention time matching on a chromatographic system with mass measurement. A reference standard of known identity is needed for a meaningful comparison. Sequence-level techniques can add further confirmation.