cyclic heptapeptide raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-02-04 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.
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.
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.
| 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 |
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.
The suspensory muscle of duodenum (also known as suspensory ligament of duodenum, Treitz's muscle or ligament of Treitz) is a thin muscle connecting the junction between the duodenum and jejunum (the small intestine's first and second parts, respectively), as well as the duodenojejunal flexure to connective tissue surrounding the superior mesenteric and coeliac arteries. The suspensory muscle most often connects to both the third and fourth parts of the duodenum, as well as the duodenojejunal flexure, although the attachment is quite variable. The suspensory muscle marks the formal division between the duodenum and the jejunum. This division is used to mark the difference between the upper and lower gastrointestinal tracts, which is relevant in clinical medicine as it may determine the source of gastrointestinal bleeding. The suspensory muscle is derived from mesoderm and plays a role in the embryological rotation of the gut, by offering a point of fixation for the rotating gut. It is also thought to help digestion by widening the angle of the duodenojejunal flexure. Superior mesenteric artery syndrome is a rare abnormality caused by a congenitally short suspensory muscle.
Bioelectrical impedance analysis (BIA) Computed tomography (CT scans) Dual-energy X-ray absorptiometry (DEXA) Magnetic resonance imaging (MRI) However, these methods are not widely used because they can be expensive and difficult to access.
Whereas the Principal Allied Powers have also agreed that the Mandatory should be responsible for putting into effect the declaration originally made on November 2nd, 1917, by the Government of His Britannic Majesty, and adopted by the said Powers, in favor of the establishment in Palestine of a national home for the Jewish people, it being clearly understood that nothing should be done which might prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country.... A statement on "British Policy in Palestine," issued on 3 June 1922 by the Colonial Office, placed a restrictive construction upon the Balfour Declaration. The statement excluded "the disappearance or subordination of the Arabic population, language or customs in Palestine" or "the imposition of Jewish nationality upon the inhabitants of Palestine as a whole", and made it clear that in the eyes of the mandatory Power, the Jewish National Home was to be founded in Palestine and not that Palestine as a whole was to be converted into a Jewish National Home. The Committee noted that the construction, which restricted considerably the scope of the National Home, was made prior to the confirmation of the Mandate by the Council of the League of Nations and was formally accepted at the time by the Executive of the Zionist Organization. The Partition Resolution of the UN General Assembly died at birth when rejected by the Arabs. The UNGA has only the power to recommend.
== See also == Bonding in solids Bresle method (the method used to test for salt presence during coating applications) Carboxylate Halide Ioliomics Ionic bonds Natron Salinity Salt metathesis reaction
Bonded leather is made by shredding leather scraps and leather fiber, then mixing it with bonding materials. The mixture is next extruded onto a cloth or paper backing, and the surface is usually embossed with a leather-like texture or grain. Color and patterning, if any, are a surface treatment that does not penetrate like a dyeing process would. The natural leather fiber content of bonded leather varies. The manufacturing process is somewhat similar to the production of paper. Lower-quality materials may suffer flaking of the surface material in as little as a few years, while better varieties are considered very durable and retain their pattern and color even during commercial use. Because the composition of bonded leathers and related products varies considerably, and is sometimes a trade secret, it may be difficult to predict how a given product will perform over the course of time. There is a wide range in the longevity of bonded leathers and related products; some better-quality bonded leathers are claimed to be superior in durability over low-quality genuine leather.
Sources: en.wikipedia.org
Iron has four stable isotopes: 54Fe (5.845% of natural iron), 56Fe (91.754%), 57Fe (2.119%) and 58Fe (0.282%). Twenty-four artificial isotopes have also been created. Of these stable isotopes, only 57Fe has a nuclear spin (−1⁄2). The nuclide 54Fe theoretically can undergo double electron capture to 54Cr, but the process has never been observed and only a lower limit on the half-life of 4.4×1020 years has been established. 60Fe is an extinct radionuclide of long half-life (2.6 million years). It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide 60Ni. Much of the past work on isotopic composition of iron has focused on the nucleosynthesis of 60Fe through studies of meteorites and ore formation. In the last decade, advances in mass spectrometry have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work is driven by the Earth and planetary science communities, although applications to biological and industrial systems are emerging. In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60Ni, the granddaughter of 60Fe, and the abundance of the stable iron isotopes provided evidence for the existence of 60Fe at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe, along with that released by 26Al, contributed to the remelting and differentiation of asteroids after their formation 4.6 billion years ago.
In popular culture, the Bro Code is a friendship etiquette to be followed among men or, more specifically, among members of the bro subculture. The notion of an unwritten set of rules that govern the relationship between straight male friends is present in modern American popular culture at least since 1991. In the Seinfeld episode "The Stranded", which aired on November 27 that year, Jerry Seinfeld says the following monologue, in one of his stand-up bits:
Members of FATF’s International Cooperation Review Group (ICRG) raised concerns that the UAE overpromised, but undelivered. However, ICRG’s representatives from the U.S. and European allies refused to address such concerns. A study by Swissaid revealed that 93% of undeclared African gold ended up in the UAE, making it the leading importer of smuggled gold from the continent. A co-author of the report, Marc Ummel said the FATF should reconsider the February 2024 removal of the Emirates from its “grey list”, as the country was illegally importing gold from Africa. He pointed out that the African gold is majorly linked to conflict, money laundering and human rights issues, leaving people extracting gold with nothing. The Irish Department of Housing urged minister Darragh O'Brien to "ask in the strongest terms for the UAE to account for its relationship to Daniel Kinahan" a drug kingpin charged along with his brother, Christopher Kinahan in 2018 by the High Court of controlling and managing the daily drug operations in Ireland. The Kinahan brothers are sons of the Kinahan Cartel founder, Christy Kinahan Senior, who smuggled drugs and firearms into the UK, Ireland, and mainland Europe for long. For several years, the Kinahan leadership had been residing in Dubai, where Daniel denied his involvement in organized crime by defending himself as a ‘high-profile businessman in the professional boxing industry'.
Normally, joint cartilages have proteoglycan complexes, which are proteins with side chains made of glycosaminoglycans such as keratan sulfate and chondroitin sulfate attached to strands of hyaluronic acid. The glycosaminoglycan side chains are polyanionic, which causes adjacent side chains to push each other away and create a "bottle brush", where hyaluronic acid is the stem and the side chains are the bristles. When pressure is exerted on the joint, fluids move between the chondrocytes and synovial fluid, exchanging nutrients. In degenerative joint disease, the proteoglycan complexes start disappearing, and the hyaluronate becomes poorer in quality and scarcer. This lowers the viscosity of the synovial fluid (which increases friction) and causes white blood cells and enzymes to enter and effect cartilage degradation and inflammation. Steroids that are released as a result kill the chondrocytes. The remaining chondrocytes have trouble exchanging nutrients with the synovial fluid, which would allow them to repair some damages. The mechanism of PSGAG in vivo is based on observations and studies in vitro. PSGAG inhibits many of the catabolic enzymes that degrade cartilage, proteoglycans, and hyaluronic acid. The enzymes that are inhibited include serine proteases, which play a role in the IL-1 degradation of proteoglycans and collagen; lysosomal enzymes that cause proteoglycans to dissociate from hyaluronic acid; elastase; metalloproteinases such as stromelysin, which degrade cartilage matrix proteins; collagenases such as cathepsin B1; and hyaluronidase.
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.
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.