cyclic heptapeptide is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2025-12-27. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Lyophilized peptide powder is generally stored frozen, protected from light and moisture. Tryptophan residues are susceptible to oxidation, and the lactam bridge can hydrolyze under strongly acidic or basic conditions. Solutions prepared for laboratory work degrade faster than dry powder, and repeated freeze-thaw cycles accelerate loss. Common practice is to aliquot solutions before freezing and to avoid alkaline buffers. Reported stability windows vary with concentration, buffer, and temperature, so exact shelf lives are method-specific rather than universal.
Regulatory status differs by country, and in many places supplying the compound for human consumption is unlawful. Vendors frequently label material as intended for research use only, a designation that shifts stated purpose but does not create a legal pathway for personal use. Certificates of analysis accompanying such products vary widely in detail and provenance. Third-party testing exists but is voluntary, and results are rarely linked to a specific lot in a publicly verifiable way.
Identity testing for a synthetic peptide relies on several complementary methods. Reversed-phase high-performance liquid chromatography separates the target from related impurities and reports purity as a percentage of total peak area. Mass spectrometry confirms molecular mass and can reveal deletions or truncations. Amino acid analysis and peptide mapping provide sequence-level confirmation, while counter-ion content and residual solvents are measured separately. A purity figure alone does not establish identity, so a complete dataset combines chromatographic and spectrometric evidence.
| Property | Value | Notes |
|---|---|---|
| Compound class | Synthetic cyclic heptapeptide | Alpha-MSH analogue containing a D-phenylalanine residue |
| Molecular formula | C50H69N15O9 | Average molecular mass approximately 1024.2 g/mol |
| Appearance | White to off-white lyophilised powder | Normally supplied as a freeze-dried solid in a sealed vial |
| Solubility | Freely soluble in water and polar solvents | Dissolves readily in aqueous buffers and in alcohol-water mixtures |
| Receptor targets | MC1R, MC3R, MC4R, MC5R | Acts as a non-selective melanocortin receptor agonist |
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.
Solid peptide kept dry at minus twenty degrees Celsius, shielded from light and moisture, is generally considered stable for extended periods. Solutions are divided into single-use aliquots and held at minus twenty or minus eighty degrees Celsius, because repeated freeze-thaw cycles promote aggregation and loss of material to container surfaces. Hydrolysis of the backbone and oxidation of tryptophan are the principal degradation routes in aqueous solution, and both accelerate at ambient temperature. Hygroscopic uptake after a vial is opened can also shift the actual mass weighed, which affects any concentration calculated from it.
Routine characterisation relies on reversed-phase high-performance liquid chromatography with ultraviolet detection near 214 nanometres, using a C18 column and a water-acetonitrile gradient containing trifluoroacetic acid. Electrospray ionisation mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidised by-products that co-elute poorly. Sequence and stereochemistry require additional work, such as peptide mapping or amino acid analysis, because a chromatographic purity figure alone does not distinguish a diastereomer from the target peptide. Independent testing of research-grade material frequently shows measured content below the stated label, so a certificate of analysis is best read together with the method that produced it.
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.
=== Familia Presto series 1 (FA3; 1970) === From April 1970, the Presto nameplate was added into the entire Familia range, "Presto" means "quick" in Italian. Brand new overhead camshaft 1.3-litre TC engine also appeared, derived from the smaller 1.0-litre OHC engine already seen in the first generation Familia coupé. At the same time, the range received a light facelift including a chrome strip around the front grille. Unlike the pickup, the vans also used the "Familia Presto" name. Chassis codes are SPCV for the 1.0-litre and STBV for the 1.3-litre model, with power outputs as for the saloon/coupé. Standard and Deluxe versions were available, with the Deluxe also offering five-door bodywork. The Familia was exported as the "Mazda 1300", and replaced the previous generation 1200 model in most markets. In Finland, the Familia Presto was marketed as the "Mazda Marella." The saloon and coupé were updated in 1972 in Japan and in the autumn of 1973 for export market, but the pickup and wagon/van versions continued with little change. The vans and pickups actually soldiered on until 1978, by which time a wagon version of the succeeding FA4 Familia (323/GLC) had been introduced. The later pickup versions were also available in a long-wheelbase version, and still featured an 85 PS (63 kW) (SAE gross) version of the 1.3-litre TC engine, unaffected by the tighter Japanese emissions standards for passenger cars. The "1200" was offered in the United States in 1971 and again for the 1973 model year.
In veterinary practice, dogs are the species most commonly affected by hypothyroidism. The majority of cases occur as a result of primary hypothyroidism, of which two types are recognized: lymphocytic thyroiditis, which is probably immune-driven and leads to destruction and fibrosis of the thyroid gland, and idiopathic atrophy, which leads to the gradual replacement of the gland by fatty tissue. There is often lethargy, cold intolerance, exercise intolerance, and weight gain. Skin changes and fertility problems are seen in dogs with hypothyroidism, as well as many other symptoms. The signs of myxedema can be seen in dogs, with prominence of skin folds on the forehead, and cases of myxedema coma are encountered. The diagnosis can be confirmed by a blood test, as the clinical impression alone may lead to overdiagnosis. Lymphocytic thyroiditis is associated with detectable antibodies against thyroglobulin, although they typically become undetectable in advanced disease. Treatment is with thyroid hormone replacement. Other species that are less commonly affected include cats and horses, as well as other large domestic animals. In cats, hypothyroidism is usually the result of other medical treatments such as surgery or radiation. In young horses, congenital hypothyroidism has been reported predominantly in Western Canada and has been linked with the mother's diet.
A metric foot, defined as 300 millimetres (approximately 11.8 inches), has been used occasionally in the UK but has never been an official unit. The corresponding metric inch of 25 millimetres (0.984 in) was used for pin spacing in Soviet microchips, which were often cloned from Western designs but scaled down slightly from US customary inches to metric inches. This led to incompatibility issues in the Soviet computer market.
=== Physical symptoms === A low body mass index (BMI) for one's age and height (except in cases of atypical anorexia) Rapid, continuous weight loss Dry hair and skin, hair thinning, as well as hair loss Low body temperature (hypothermia) Raynaud Phenomenon Hypotension or orthostatic hypotension Bradycardia or tachycardia Chronic fatigue Insomnia Severe muscle tension, aches and pains Irregular or absent menstrual periods in women Infertility Gastrointestinal disease Halitosis (from vomiting or starvation-induced ketosis) Abdominal distension Russell's Sign; can be a tell-tale sign of self-induced vomiting with scratches on the back of the hand Tooth erosion Lanugo: soft, fine hair growing over the face and body Orange discoloration of the skin, particularly the feet (carotenosis)
Sources: en.wikipedia.org
For example, furan-2-ylmethanethiol contributes to the aroma of roasted coffee, whereas grapefruit mercaptan, a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit. The effect of the latter compound is present only at low concentrations. Concentrated samples have an unpleasant odor. In the United States, distributors are required to add thiols, originally ethanethiol, to natural gas (which is naturally odorless) after the deadly New London School explosion in New London, Texas, in 1937, although many distributors were odorizing gas prior to this event. Most currently-used gas odorants contain mixtures of mercaptans and sulfides, with t-butyl mercaptan as the main odor constituent in natural gas and ethanethiol in liquefied petroleum gas (LPG, propane). In situations where thiols are used in commercial industry, such as liquid petroleum gas tankers and bulk handling systems, an oxidizing catalyst is used to destroy the odor. A copper-based oxidation catalyst neutralizes the volatile thiols and transforms them into inert products.
==== Challenge ==== Finding a specific molecule that selectively inhibits the activity of a certain E3 ligase and/or the protein–protein interactions implicated in the disease remains as an expanding research area. Moreover, as ubiquitination is a multi-step process with various variables and intermediate forms, consideration of the much complex interactions between components is advised to be taken heavily into account while designing the small molecule inhibitors.
Chalcone synthase or naringenin-chalcone synthase (CHS) is an enzyme ubiquitous to higher plants and belongs to a family of polyketide synthase enzymes (PKS) known as type III PKS. Type III PKSs are associated with the production of chalcones, a class of organic compounds found mainly in plants as natural defense mechanisms and as synthetic intermediates. CHS was the first type III PKS to be discovered. It is the first committed enzyme in flavonoid biosynthesis. The enzyme catalyzes the conversion of 4-coumaroyl-CoA and malonyl-CoA to naringenin chalcone.
Two-dimensional SDS-PAGE uses the principles and techniques outlined above. 2-D SDS-PAGE, as the name suggests, involves the migration of polypeptides in 2 dimensions. For example, in the first dimension, polypeptides are separated according to isoelectric point, while in the second dimension, polypeptides are separated according to their molecular weight. The isoelectric point of a given protein is determined by the relative number of positively (e.g. lysine, arginine) and negatively (e.g. glutamate, aspartate) charged amino acids, with negatively charged amino acids contributing to a low isoelectric point and positively charged amino acids contributing to a high isoelectric point. Samples could also be separated first under nonreducing conditions using SDS-PAGE, and under reducing conditions in the second dimension, which breaks apart disulfide bonds that hold subunits together. SDS-PAGE might also be coupled with urea-PAGE for a 2-dimensional gel. In principle, this method allows for the separation of all cellular proteins on a single large gel. A major advantage of this method is that it often distinguishes between different isoforms of a particular protein – e.g. a protein that has been phosphorylated (by addition of a negatively charged group). Proteins that have been separated can be cut out of the gel and then analysed by mass spectrometry, which identifies their molecular weight.
=== Interactions with Solvent === Increasing addition of solute will alter the solvent's viscosity and polarizability, which cannot be measured by instruments that rely on low viscosity. Since differential refractometer is an external tool, the solvent viscosity does not pose a physical barrier to measurement, making them universal detectors.
Sources: en.wikipedia.org
No. It is a laboratory-made peptide, while the natural hormone is alpha-melanocyte-stimulating hormone, a longer peptide produced by the pituitary gland and by skin cells. Melanotan-2 mimics only a short active region of that hormone and contains non-natural residues such as D-phenylalanine.
No approved regulatory indication exists in major markets. An approval exists for a different peptide, afamelanotide, which is used for a rare photosensitivity disorder called erythropoietic protoporphyria. Melanotan-2 itself remains a research compound with no cleared clinical role.
Melanocortin-1 receptors on melanocytes are the receptor most closely linked to pigment production. The peptide is not selective, however, and also activates melanocortin-3, melanocortin-4, and melanocortin-5 receptors. That lack of selectivity is the usual explanation offered for both its range of observed effects and its off-target effects.
Dry powder is usually held frozen, shielded from light, and kept away from moisture. Desiccant packaging limits hydrolysis during storage. Solutions are typically aliquoted and frozen once, because repeated thawing shortens useful life.