Everything below concerns melanocortin receptor. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Free base; salt forms differ |
| Molecular weight | Approximately 1024 g/mol | Calculated for the free base |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water and polar solvents | Poorly soluble in non-polar solvents |
| Typical storage | -20 degrees Celsius, dry, protected from light | Refers to the solid form |
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 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.
Collagenase clostridium histolyticum is an enzyme produced by the bacterium Clostridium histolyticum that dismantles collagen. It is used as a powder-and-solvent injection kit for the treatment of Dupuytren's contracture, a condition where the fingers bend towards the palm and cannot be fully straightened, and Peyronie's disease, a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis. BioSpecifics Technologies developed the preparation, which is manufactured and marketed by Endo Pharmaceuticals as Xiaflex in the US and by Sobi as Xiapex in Europe. Biochemically, it is a mixture of two C. histolyticum collagenases, ColH and ColG. A similar ointment preparation called Santyl contains one or many collagenases from the same bacterium, but it is unclear which.
==== Anti-seizure medication ==== The anti-convulsant medications gabapentin and pregabalin may be used to reduce pain. There is tentative evidence that gabapentin may be of benefit for pain in about 18% of people with fibromyalgia. It is not possible to predict who will benefit, and a short trial may be recommended to test the effectiveness of this type of medication. Approximately 6/10 people who take gabapentin to treat pain related to fibromyalgia experience unpleasant side effects such as dizziness, abnormal walking, or swelling from fluid accumulation. Pregabalin demonstrates a benefit in about 9% of people, it may also enhance sleep quality. Pregabalin reduced time off work by 0.2 days per week. A 2025 review found that, for enhancing sleep quality in FM, pregabalin might be beneficial but had potential risks.
Distillation of chemicals such as in petroleum refining is done in towers or columns with perforated trays. Vapor from the low boiling fractions bubbles upward through the holes in the trays in contact with the down flowing high boiling fractions. The concentration of low boiling fraction increases in each tray up the tower as it is "stripped". The low boiling fraction is drawn off the top of the tower and the high boiling fraction drawn from the bottom. The process in the trays is a combination of heat transfer and mass transfer. Heat is supplied at the bottom, known as a "reboiler" and cooling is done with a condenser at the top.
== Structure and general properties == L- and D-amino acids are usually enantiomers. The exceptions are two amino acids with two stereogenic centers, threonine and isoleucine. Aside from those two special cases, L- and D-amino acids have identical properties (color, solubility, melting point) under many conditions. In the biological context however, which is chiral, these enantiomers can behave very differently. Thus, D-amino acids have low nutritional value, in part because they are not digested well. They contain a carboxyl group at one end and a side chain group at the other end. They also contain an amine and hydrogen group on opposite ends, depending on which enantiomer one is looking at. They also do attain a chiral carbon center. This is why the molecules can exist in different stereoisomeric forms, and the orientation of the radical groups is what is only different between these enantiomers. D-glyceraldehyde on the other hand, contains a carbonyl group and hydroxy (alcohol) groups with the chiral carbon in the center. The orientation is again, different for L-glyceraldehyde.
Sources: en.wikipedia.org
=== Macrocycles === Macrocycles are a traditional component in supramolecular chemistry. The macrocyclic effect enhances otherwise weak interactions. Cyclodextrins, calixarenes, cucurbiturils, and crown ethers allow the incorporation of alkali metal cations. More complex, 3-dimenesion receptors include cyclophanes, and cryptands. Supramolecular metallocycles and metallacrowns are related components. Common metallocycle shapes in these types of applications include triangles, squares, and pentagons, each bearing functional groups that connect the pieces via "self-assembly."
The ratio of carbon isotopes in humans varies according to the types of plants digested with different photosynthesis pathways. The three photosynthesis pathways are C3 carbon fixation, C4 carbon fixation and Crassulacean acid metabolism. C4 plants are mainly grasses from tropical and subtropical regions, and are adapted to higher levels of radiation than C3 plants. Corn, millet and sugar cane are some well-known C4 crops, while trees and shrubs use the C3 pathway. C4 carbon fixation is more efficient when temperatures are high and atmospheric CO2 concentrations are low. C3 plants are more common and numerous than C4 plants as C3 carbon fixation is more efficient in a wider range of temperatures and atmospheric CO2 concentrations. The different photosynthesis pathways used by C3 and C4 plants cause them to discriminate differently towards 13C leading to distinctly different ranges of δ13C. C4 plants range between -9 and -16‰, and C3 plants range between -22 and -34‰. The isotopic signature of consumer collagen is close the δ13C of dietary plants, while apatite, a mineral component of bones and teeth, has an ~14‰ offset from dietary plants due fractionation associated with mineral formation. Stable carbon isotopes have been used as tracers of C4 plants in paleodiets. For example, the rapid and dramatic increase in 13C in human collagen after the adoption of maize agriculture in North America documents the transition from a C3 to a C4 (native plants to corn) diet by 1300 CE.
== Awards == Prix scientifique de la Fondation de France, with André Langaney, 1978 Prix de la Société française de physique, 1985 Le Relictocarabus meurguesianus, and insect discovered in Morocco, was named in her honour.
The 1993 film Jurassic Park (based on the 1990 Michael Crichton novel of the same name) features dinosaurs that were genetically altered so that they could not produce the amino acid lysine. This was known as the "lysine contingency" and was supposed to prevent the cloned dinosaurs from surviving outside the park, forcing them to be dependent on lysine supplements provided by the park's veterinary staff. In reality, no animals are capable of producing lysine (it is an essential amino acid). Autotroph Bradytroph "Regulation of endosomal clathrin and retromer-mediated endosome to Golgi retrograde transport by the J-domain protein RME-8" - The EMBO Journal "Pleiotropic effects of purine auxotrophy inRhizobium meliloti on cell surface molecules" - Springerlink "Auxotrophy and Organic Compounds in the Nutrition of Marine Phytoplankton"
=== Nuclear isomers, including a "stable" one === The 251 known stable nuclides include tantalum-180m, since even though its decay is automatically implied by it being "metastable", this has not been observed. All "stable" isotopes (stable by observation, not theory) are the ground states of nuclei, except for tantalum-180m, which is a nuclear isomer or excited state. The ground state, tantalum-180, is radioactive with half-life 8 hours; in contrast, the decay of the nuclear isomer is extremely strongly forbidden by spin-parity selection rules. It has been reported by direct observation that the half-life of 180mTa to gamma decay must be >1015 years. Other possible modes of 180mTa decay (beta decay, electron capture, and alpha decay) have also never been observed.
Sources: en.wikipedia.org
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.
Both are synthetic analogues derived from the same parent hormone. Reference descriptions usually characterise afamelanotide as more selective for the MC1R subtype, whereas melanotan-2 is reported to interact with a wider range of melanocortin receptors.
Early studies explored melanocortin signalling and pigmentation, which later led to informal use of the label tanning peptide. That label is not a regulatory category and does not imply approved status for any purpose.
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.