cyclic peptide 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 2026-03-26 and is reviewed periodically as new material appears.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Melanotan II; MT-II; N-acetyl-norleucyl-cyclo[Asp-His-D-Phe-Arg-Trp-Lys] amide | Naming follows peptide convention; the numeral distinguishes it from melanotan-1 |
| Molecular formula | C50H69N15O9 | Includes the lactam bridge; no counter-ion assumed |
| Monoisotopic mass | 1023.53 Da | Free base; salts and counter-ions shift the observed value |
| Appearance | White to off-white lyophilised powder | Batch-to-batch colour variation is not itself proof of impurity |
| Typical analytical method | RP-HPLC purity determination with ESI-MS identity confirmation | Retention time alone does not establish sequence identity |
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.
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.
The compound emerged from research programs in the 1980s that examined analogues of alpha-melanocyte-stimulating hormone for pigmentation and photoprotection. Investigators modified the native sequence to extend activity duration and potency. A related analogue, afamelanotide, was developed within the same broad line of inquiry and eventually gained approval in certain jurisdictions for a rare light-sensitivity condition. Melanotan-2 itself did not progress through the same regulatory route and has no approved therapeutic indication.
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.
== Sports == Canberra Raiders, Australian rugby league football club Chitwan Rhinos, a professional Twenty20 cricket franchise representing Chitwan District, Nepal in the Nepal Premier League (NPL) Colorado Rockies, a Major League Baseball team Cincinnati Reds, another Major League Baseball team Colorado Rockies (NHL), a former National Hockey League team Cristiano Ronaldo, Portuguese footballer Commonwealth record in athletics Commonwealth record in swimming
The new 31st district is anchored in the northern exurbs of Austin (including Georgetown and Burnet) and stretches northward to Killeen and most of Temple along with Fort Hood, going as far north as Hamilton. The incumbent is Republican John Carter, who was re-elected with 64.5% of the vote in 2024. That same year, Donald Trump won 60.1% and Ted Cruz 57.6% of the vote, respectively.
In February 2023, French Foreign Minister Catherine Colonna met with President Lula and stated that "Brazil is one of the main actors on the global stage and its comeback is highly expected", highlighting that France and Brazil share a strong, centuries-old relationship. She also said that France supports a Brazilian OECD membership and that both France and the European Union are considering monetary contributions to the Amazon Fund. On 11 February, French president Emmanuel Macron expressed his approval for a peace plan on the Russia-Ukraine war proposed by Lula, which consists of creating a group of countries not involved in the conflict (either directly or indirectly, i.e. by sending weapons to one of the sides) to mediate a peace process. On 3 June 2023, Macron's office said Lula confirmed he would visit Paris in late June as part of the "Summit for a New Global Financial Pact" promoted by France to "tackle the reform of multilateral development banks (MDB), the debt crisis, financing for green technologies, the creation of new international taxes and financing instruments", among other things. On 22 June, president Lula delivered a speech during the Power Our Planet festival in Paris in which he said "actually, those who have polluted the planet over the last two centuries are the same ones who made the Industrial Revolution, and that's why they must pay their debt to the planet Earth" while calling for climate justice to Latin-American, African and Asian peoples and inviting the world to attend the COP30 climate conference in the Brazilian city of Belém.
American kestrels in Canada and the northern United States typically migrate south in the winter, some of them converging with resident kestrels of smaller size in Mexico, sometimes going as far as Central America and the Caribbean. Birds that breed south of about 35° north latitude are usually year-round residents. Migration also depends on local weather conditions. American Kestrels breeding at lower latitudes – below 48ºN to be precise – arrive earlier after warmer springs, whereas birds from higher latitudes return to their breeding grounds at the same time each year. These patterns suggest that short-distance migrants are better able to cope with climate change. Wintering kestrels' choice of habitat varies by sex. Females are found in open areas more often than males during the non-breeding season. A common explanation for this behavior is that the larger females who are bigger than the males arrive at the preferred habitat first and exclude males from their territory. The American kestrel is not long-lived, with a lifespan of <5 years for wild birds. The oldest banded wild bird was 11 years and 7 months, while captive kestrels can live up to 14–17 years. In a study, humans accounted for 43.2% of 1,355 reported deaths, which included direct killing and roadkills, while predation (including by larger birds of prey) accounted for 2.8%. This statistic is likely biased, however, as reported deaths are usually found near or in areas populated by humans.
Walker attended RMIT University in Melbourne, Australia. Together with John Cook and Ian Caughley, Walker started working on Team Fortress as a mod for id Software's QuakeWorld in 1996. Due to the popularity of the product, the team was hired by the then-small Valve to work on Team Fortress Classic and later on Team Fortress 2. Walker has played development roles in various Valve games, including Half-Life 2 and Dota 2. More recently, Walker has been focused on the collision of economics and game design, in an attempt to transform Team Fortress 2 into a free-to-play, microtransaction-based game. Walker worked on Valve's flagship virtual reality game, Half-Life: Alyx, released on 23 March 2020.
Sources: en.wikipedia.org
== Intracrines in biology and cancer == Intracrines involvement in cancer is primarily through their regulation of growth factors, angiogenesis, and cellular signaling networks that contribute to tumor growth and therapy resistance.
The Mystery of the Yellow Room (French: Le mystère de la chambre jaune) is a mystery novel written by French author Gaston Leroux. One of the first locked-room mystery novels, it was first published serially in France in the periodical L'Illustration from September 1907 to November 1907, then in its own right in 1908. It is the first novel starring fictional reporter Joseph Rouletabille and concerns a complex, and seemingly impossible, crime in which the criminal appears to disappear from a locked room. Leroux provides the reader with detailed, precise diagrams and floorplans illustrating the crime scene. The story provides an intellectual challenge to the reader. The novel finds its continuation in the 1908 novel The Perfume of the Lady in Black, wherein a number of the characters familiar from this story reappear.
== History as a biological model == Mice have been used in biomedical research since the 17th century, when William Harvey used them for his studies on reproduction and blood circulation and Robert Hooke used them to investigate the biological consequences of an increase in air pressure. During the 18th century, Joseph Priestley and Antoine Lavoisier both used mice to study respiration. In the 19th century, Gregor Mendel carried out his early investigations of inheritance on mouse coat color but was asked by his superior to stop breeding in his cell "smelly creatures that, in addition, copulated and had sex". He then switched his investigations to peas, but, as his observations were published in a somewhat obscure botanical journal, they were virtually ignored for over 35 years until they were rediscovered in the early 20th century. In 1902, Lucien Cuénot published the results of his experiments using mice which showed that Mendel's laws of inheritance were also valid for animals — results that were soon confirmed and extended to other species. In the early part of the 20th century, Harvard undergraduate Clarence Cook Little was conducting studies on mouse genetics in the laboratory of William Ernest Castle. Little and Castle collaborated closely with Abbie Lathrop, a breeder of fancy mice and rats which she marketed to rodent hobbyists and keepers of exotic pets, and later began selling in large numbers to scientific researchers. Together, they generated the DBA (Dilute, Brown and non-Agouti) inbred mouse strain and initiated the systematic generation of inbred strains.
Line 14: Since 10 September 2016, the Moscow Central Circle (MCC) renovated railroad (the former Moskovskaya Okruzhnaya Zheleznaya Doroga) has been operated as Line 14 of the Moscow Metro. This cone-shaped railroad opened in 1908 (as a freight-only railway from 1934 until the reopening in 2016). Line 11: Another circular metro line—the Big Circle Line (Bolshaya Koltsevaya Liniya)—opened its first stations in 2018 and the remaining stations in 2023. The Kakhovskaya-Savyolovskaya western half of the line was launched in late 2021. The outermost ring within the city is the Moscow Ring Road—often called the MKAD, an acronym for the Russian Московская Кольцевая Автомобильная Дорога—which forms the city's cultural boundary; it was established during the 1950s. It was built at ground level, rather than being elevated, so it forms a barrier to roads that would otherwise pass beneath it. (Before Moscow's 2012 expansion, the MKAD was considered an approximate city boundary.) Outside Moscow, some roads encompassing the city follow the same circular pattern as within city limits; notable examples are the Betonka roads (highways A107 and A108), originally constructed of concrete pads. To reduce traffic on the MKAD, a new ring road—called CKAD, Centralnaya Koltsevaya Avtomobilnaya Doroga, Central Ring Road—was completed outside the MKAD in 2021.
Sources: en.wikipedia.org
2A peptides are a class of 18–22 aa-long peptides, which can induce ribosomal skipping during translation of a protein in a biological cell. These peptides share a core sequence motif of DxExNPGP, and are found in a wide range of viral families. 2A peptides can be introduced artificially to help generate polyproteins from a single ORF, by causing the ribosome to fail at making a peptide bond, and then resume translation. The members of 2A peptides are named after the virus in which they have been first described. For example, F2A, the first described 2A peptide, is derived from foot-and-mouth disease virus. The name "2A" itself comes from the gene numbering scheme of this virus. These peptides are also known as "self-cleaving" peptides, which is a known misnomer, because the missing peptide bond is never synthesized by the ribosome, and is thus not cleaved.
=== Influence on the Democratic Party === Analysts have suggested that Sanders's campaign shifted both the Clinton campaign and the Democratic Party politically leftward. A new political organization, Brand New Congress, was formed in April 2016 by former campaign staffers. It works to elect congressional representatives with platforms in line with Sanders. In August 2016, he formed Our Revolution, a political organization dedicated to educating voters about issues, getting people involved in the political process, and electing progressive candidates for local, state, and national office. Speaking on the PBS Newshour about the upcoming 2018 elections and discussing the main principles of the two major parties, Susan Page described the Republican Party as "Trump's party" and the Democratic Party as "Bernie Sanders's party", saying that "Sanders and his more progressive stance has really taken hold." Noting the increasing acceptance of his national single-payer health-care program, his $15-an-hour minimum wage stance, free college tuition, and many of the other campaign platform issues he introduced, an April 2018 opinion article in The Week suggested, "Quietly but steadily, the Democratic Party is admitting that Sanders was right." In July 2016, a Slate article called the Democratic platform draft "a monument to his campaign", noting not only his call for a $15 minimum wage but other campaign issues, such as Social Security expansion, a carbon tax, Wall Street reform, opposition to the death penalty, and a "reasoned pathway for future legalization" of marijuana.
== Side effects == Methyldopa is capable of inducing a number of adverse side effects, which range from mild to severe. Nevertheless, they are generally mild when the dose is less than 1 gram per day. Side effects may include:
The two substrates of this enzyme are D-sorbitol and oxidised nicotinamide adenine dinucleotide phosphate (NADP+). Its products are L-sorbose (shown in open-chain keto form), reduced NADPH, and a proton. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is D-glucitol:NADP+ oxidoreductase. This enzyme is also called Sou1p.
March 26 Nicolás Maduro and his wife Cilia Flores appear in a New York federal court for their latest hearing, faced with charges of narcoterrorism and weapons offenses. Treasury Secretary Bessent announces that Trump's signature will appear on U.S. paper currency, the first time a sitting president's signature will appear instead of the Treasurer and Secretary of the Treasury. March 27 A House Ethics Committee panel finds that Florida Democratic Representative Sheila Cherfilus-McCormick committed ethics violations in misappropriating federal disaster money for her re-election campaign. A federal appeals court overturns a $16.1 billion judgment against Argentina over their nationalization of oil firm YPF. March 28 Protests against Donald Trump: The third No Kings protests are held in all 50 U.S. states against the policies of Trump and his administration including the Iran war, ICE operations, and the January shootings of Renée Good and Alex Pretti. In the NCAA Tournament, the Arizona Wildcats reach the Final Four for the first time since 2001. Additionally, Illinois reaches the Final Four for the first time since 2005. 3,500 U.S. troops arrive in the Middle East with the USS Tripoli (LHA-7), as strikes between Israel and Iran continue. March 30 – Trump and his son Eric unveil the plans for Trump's presidential library in Miami, Florida, at the Miami Dade College campus. Trump plans for the library to also be a hotel. March 31 AAA reports the average price of gas in the United States has risen to $4 a gallon for the first time since 2022.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, containing seven amino acids with a lactam ring and a D-configured phenylalanine residue. It is supplied as a lyophilised powder for laboratory research.
The natural hormone is a linear tridecapeptide that is rapidly degraded in circulation. Melanotan-2 is shortened, cyclised, N-terminally acetylated, and carries a D-amino acid substitution, all of which slow enzymatic breakdown.
No national medicines regulator has approved melanotan-2 for therapeutic or cosmetic use. In several jurisdictions it is treated as an unapproved prescription medicine, and its legal classification differs from country to country.
It is a synthetic seven-amino-acid peptide modeled on alpha-melanocyte-stimulating hormone. It carries two non-natural substitutions and a cyclic bridge that increase its stability relative to the natural hormone. It circulates as a research chemical and is not an approved medicine.