This is a working overview of cyclic heptapeptide, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-11. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| 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 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 a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous tridecapeptide that regulates pigment production. Two modifications distinguish it from the natural hormone: norleucine replaces methionine at the N-terminus, which limits oxidation, and a D-phenylalanine substitution raises receptor affinity. The ring is closed through an aspartate-lysine lactam bridge, giving the molecule a constrained conformation. The free base has a molecular mass near 1024 daltons, and commercial material is usually supplied as an acetate salt. It appears in the literature as a research peptide rather than an approved therapeutic agent.
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.
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 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.
=== Etymology === Mocro maffia: The name "Mocro maffia" is given by the Dutch-speaking authorities in the Netherlands and Belgium, who refer to Moroccan criminal organisations operating in the Benelux. The term was made public by author Martijn Schrijver in 2013, following the publication of his book Mocro Maffia, released in 2014. However, the term "Mocro" has existed since the 1990s, and is a Moroccan-Dutch slang term that describes someone with a Moroccan immigrant background, in both Belgium and the Netherlands. The term "Mocro Maffia" does not make a distinction between the various organisations that rival each other, but instead describes a network of all Moroccan criminal organisations that are active in the Benelux. Although the majority of members are of Moroccan descent, there are also some members who are from Dutch, Antillean, or Surinamese background. Mocro-oorlog or Mocro-War (Moroccan war): The name by which the media and journalists refer to the Mocro mafia conflict that began in 2012. Borgerokko Maffia: The name by which politicians, media outlets, and journalists refer to the Moroccan criminal networks that are active in Antwerp. The term was adopted by the Belgian writer Raf Sauviller in his book Borgerokko Maffia, which was released in 2017. The term quickly appeared on the front pages of Belgian newspapers.
In the physical sciences, the spectrum of a physical quantity (such as energy) may be called continuous if it is non-zero over the whole spectrum domain (such as frequency or wavelength) or discrete if it attains non-zero values only in a discrete set over the independent variable, with band gaps between pairs of spectral bands or spectral lines. The classical example of a continuous spectrum, from which the name is derived, is the part of the spectrum of the light emitted by excited atoms of hydrogen that is due to free electrons becoming bound to a hydrogen ion and emitting photons, which are smoothly spread over a wide range of wavelengths, in contrast to the discrete lines due to electrons falling from some bound quantum state to a state of lower energy. As in that classical example, the term is most often used when the range of values of a physical quantity may have both a continuous and a discrete part, whether at the same time or in different situations. In quantum systems, continuous spectra (as in bremsstrahlung and thermal radiation) are usually associated with free particles, such as atoms in a gas, electrons in an electron beam, or conduction band electrons in a metal. In particular, the position and momentum of a free particle has a continuous spectrum, but when the particle is confined to a limited space its spectrum becomes discrete. Often a continuous spectrum may be just a convenient model for a discrete spectrum whose values are too close to be distinguished, as in the phonons in a crystal.
=== Media === In August 2015, journalist David de Sola published the biography Alice in Chains: The Untold Story. An updated version covering the period from 2014 to 2017 was published in November 2018. Neither the band nor their management had any involvement with the book. Sources tied directly to the band were interviewed instead. The claymation dolls of the band members used in the music video for "I Stay Away" are on display at the Rock and Roll Hall of Fame museum in Cleveland, Ohio.
Sources: en.wikipedia.org
The Trails of Cold Steel arc follows Rean Schwarzer and Class VII, a specialized group of students attending Thors Military Academy in the Erebonian Empire. The first game, Trails of Cold Steel was released for the PlayStation 3 and PlayStation Vita in Japan in 2013. Trails of Cold Steel II is a direct continuation of the first game and was released for the PlayStation 3 and Vita in 2014. The third and fourth games, Trails of Cold Steel III and IV, follow Rean in his new role as an instructor of a new Class VII at a branch campus of Thors. Cold Steel III was released for the PlayStation 4 (PS4) in Japan in 2017, while Cold Steel IV was released in the following year. A fifth game, Trails into Reverie, was released in 2020 and acts as an epilogue to both the Crossbell and Erebonia arcs and follows Rean, Lloyd, and a masked character known as C. English versions of Cold Steel and Cold Steel II were released by Xseed Games in 2015 and 2016, respectively. NIS America released Cold Steel III in 2019, IV in 2020, and Trails into Reverie in 2023. A box set containing all five games was released in Japan for the PS4 in July 2022.
=== Political activism === In 2018, she became spokesperson of the On est prêt collective. She spoke at the European Parliament, notably alongside Greta Thunberg, Belgians Adélaïde Charlier and Anuna De Wever and the German Luisa Neubauer. It was at Sciences Po Paris that Camille turned her attention to the climate crisis. She became president of the student branch of Amnesty International. She was also elected, in 2018, to the student organisation NOVA. During lockdown, she created the collective 'Avant l'orage' (Before the Storm) which aims to bring together art and environmentalism. On 28 May 2020 the collective's YouTube channel released a video titled Wake Up. The video, filmed in the mountains, features the activist with a dancer and engineering graduate, Léa Durand. Camille speaks about the climate emergency and reminds viewers, particularly those from Generation Z, on the need to act. Her words are accompanied by movements from the dancer. The video was a success, gaining 15 million views on various platforms and has been translated into Spanish, English, German and Portuguese. In August 2020, while speaking at the Medef summer school, she suggested "working less, but maybe with more meaning" to "reinvent" the world of business. She also questions the economic growth model, which, according to her, pushes us to "produce too much", "exceed planetary limits" and so "directly endangers our lives".
1991: Doris Malkin Curtis became the first female president of the Geological Society of America. 1991: Indian geologist Sudipta Sengupta became the first female scientist to receive the Shanti Swaroop Bhatnagar Award in the Earth Sciences category. 1991; British chemist and cosmonaut Helen Patricia Sharman became the first woman to visit the Mir space station in May 1991. 1992: American engineer, physician, and NASA astronaut Mae Carol Jemison became the first black woman to travel into space when she served as a mission specialist aboard the Space Shuttle Endeavour. Jemison joined NASA's astronaut corps in 1987 and was selected to serve for the STS-47 mission, during which she orbited the Earth for nearly eight days on September 12–20, 1992. 1992: American chemist Edith M. Flanigen became the first woman awarded the Perkin Medal (widely considered the highest honor in American industrial chemistry) for her outstanding achievements in applied chemistry. The medal especially recognized her syntheses of aluminophosphate and silicoaluminophosphate molecular sieves as new classes of materials. 1993: American molecular biologist and biogerontologist Cynthia Kenyon discovered that a single-gene mutation (Daf-2) could double the lifespan of C. elegans, and that this could be reversed by a second mutation in daf-16m. 1995: German biologist Christiane Nüsslein-Volhard received the Nobel Prize in Physiology or Medicine, shared with Edward B. Lewis and Eric F. Wieschaus, "for their discoveries concerning the genetic control of early embryonic development".
Sources: en.wikipedia.org
Psilocybe semilanceata fruits solitarily or in groups on rich and acidic soil, typically in grasslands, such as meadows, pastures, or lawns. It is often found in pastures that have been fertilized with sheep or cow dung, although it does not typically grow directly on the dung. P. semilanceata, like all others species of the genus Psilocybe, is a saprobic fungus, meaning it obtains nutrients by breaking down organic matter. The mushroom is also associated with sedges in moist areas of fields, and it is thought to live on the decaying root remains. At least one study has demonstrated an association of P. semilanceata with the roots of the grasses Agrosiis tenuis, Poa annua, and the dicot Lolium perenne. Like some other grassland psilocybin mushroom species such as P. mexicana, P. tampanensis and Conocybe cyanopus, P. semilanceata may form sclerotia, a dormant form of the fungus, which affords it some protection from wildfires and other natural disasters. Laboratory tests have shown P. semilanceata to suppress the growth of the soil-borne water mold Phytophthora cinnamomi, a virulent plant pathogen that causes the disease root rot. When grown in dual culture with other saprobic fungi isolated from the rhizosphere of grasses from its habitat, P. semilanceata significantly suppresses their growth. This antifungal activity, which can be traced at least partly to two phenolic compounds it secretes, helps it compete successfully with other fungal species in the intense competition for nutrients provided by decaying plant matter.
== Catalytic mechanism == Although the exact mechanism of ADAM10 has not been thoroughly investigated, its active site is homologous to those of well studied zinc-proteases such as carboxypeptidase A and thermolysin. Therefore, it is proposed that ADAM10 utilizes a similar mechanism as these enzymes. In zinc proteases, the key catalytic elements have been identified as a glutamate residue and a Zn2+ ion coordinated to histidine residues. The proposed mechanism begins with deprotonation of a water molecule by glutamate. The resultant hydroxide initiates a nucleophilic attack on a carbonyl carbon on the peptide backbone, producing a tetrahedral intermediate. This step is facilitated by electron withdrawal from oxygen by Zn2+ and by zinc's subsequent stabilization of the negative charge on the oxygen atom in the intermediate state. As electrons move down from the oxygen atom to re-form the double bond, the tetrahedral intermediate collapses to products with protonation of -NH by the glutamate residue.
In electron ionization (EI), energetic electrons are produced by a hot cathode: a wire filament heated by running electric current through it, producing energetic electrons by thermionic emission. The electrons are then accelerated towards an anode. The voltage difference between the cathode and the anode determines the energy of the electron stream. Most organic compounds have ionization energy 8-15 eV, but empirically, the efficiency of ionization is too low unless the electron beam has an energy of 50-70 eV per electron. The spectral features, including fragmentation patterns, depend on the energy setting. Conventionally for EI, the electron energy is standardized to be exactly 70 eV. Consequently, if one wishes to compare their EI-MS results against standard databases, or produce results that can be added to standard databases, one must standardize their EI electron energy to 70 eV. EI accepts as input a stream of gas from the molecular leak. The gas stream crosses the electron stream perpendicularly. The collision ionizes the gas stream. The ion stream then is accerelated by a succession of electrodes. Typically an ion carrying 1 e would be accelerated to 1-10 keV. EI has many benefits for routine mass spectrometry of small organic molecules. It is cheap and robust, with reproducible spectrograms. Databases for EI spectrograms are widely available and covers many such molecules. EI is unsuited for large molecules, such as most biomolecules.
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.
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.