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 2026-02-11. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
Reported observations after unregulated use include shifts in skin pigmentation and, in some accounts, unintended changes to moles and other lesions. Whether these outcomes are causally linked to the compound, and how often they occur, remain open questions because controlled data are scarce. The absence of standardised dosing and verified product purity complicates interpretation. Researchers have called for better surveillance and analytical characterisation of samples obtained outside regulated channels. Conclusions drawn from anecdotal evidence should be treated as provisional.
Melanotan-2 has not received marketing authorisation from major regulatory agencies for any therapeutic indication. Several jurisdictions classify it as a prescription-only medicine or a controlled substance when supplied for human use. Because approved products do not exist, material sold online usually sits outside pharmaceutical supply chains and formal quality oversight. Regulators have issued public notices describing the compound as unapproved. Enforcement varies, and the legal position differs between countries, which complicates any single general statement about its status.
| 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 |
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.
Regulatory treatment varies by country. In the United States the peptide is not approved as a medicine, and products offered for human use may be treated as unapproved new drugs; some states also restrict sale. Australia, the United Kingdom, and European Union member states apply comparable restrictions to unapproved peptide products. Border agencies have seized shipments labelled as research chemicals. Classification may change over time, and the legal position for personal importation is not clearly settled in most published guidance.
Lyophilised melanotan-2 is supplied as a solid, which is more stable than a solution. The material is hygroscopic, so weighing is done quickly, in low humidity, with the container kept sealed. Reconstitution usually uses water for injection or bacteriostatic water, added down the wall of the vial to limit foaming. A reconstituted solution is held at 2 to 8 °C and kept away from light. Repeated freezing and thawing of the same vial is avoided because ice crystal formation and concentration effects degrade the peptide.
No regulatory authority has approved melanotan-2 for human use, and several countries classify it as a prescription-only or controlled substance, which restricts lawful supply. Material sold online is generally labelled as a research chemical and is not required to meet pharmaceutical standards of identity or purity. Published human data consist mainly of small uncontrolled studies, case reports and adverse-event notifications, so the evidence base is descriptive rather than confirmatory. Whether repeated melanocyte stimulation alters long-term naevus behaviour remains an open question that no completed trial has resolved.
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.
=== Stan Burley === Stan Burley (Joel Gretsch) is an NCIS agent who first appears in the first-season episode "High Seas". Prior to the series' start, he was Gibbs' partner and subordinate, but eventually was transferred out as an Agent Afloat, when he was replaced by DiNozzo. He looks up to Gibbs, and enlists his and his teams' help in tracking down a drug dealer on board the USS Enterprise. Burley knew (or at least knew of) Mike Franks, and calls Gibbs following his death to express his condolences. Over eight years after his first appearance, Burley returns in the season nine episode "Playing with Fire", where he leads DiNozzo and David in tracking down and thwarting a terrorist who tries to destroy the carrier USS Benjamin Franklin in Naples, Italy, under the orders of businessman Harper Dearing. Burley is injured by the terrorist in the process. He returns with DiNozzo and David to the Navy Yard, and is part of the crowd which sees Gibbs place Dearing's photo on the wall of NCIS Most Wanted.
=== Pharmacokinetics === The bioavailability of lemborexant is good and is at least 87%. The time to peak levels of lemborexant is 1 to 3 hours. A high-fat and high-calorie meal has been found to delay the time to peak levels by 2 hours. Its plasma protein binding in vitro is 94%. Lemborexant is metabolized primarily by CYP3A4 and to a lesser extent by CYP3A5. The "effective" half-life of lemborexant is 17 to 19 hours while its terminal elimination half-life is 55 hours. The medication is excreted in feces (57%) and to a lesser extent urine (29%).
=== Pharmacodynamics === In rabbits, 2,3-dihydro-LSD had about 4% (1/25th) of the potency of LSD in inducing hyperthermia, while in mice, it was "equally toxic" (presumably referring to LD50Tooltip median lethal dose) as LSD.
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A buffer buffers most effectively around its pKa value, so the pKa of the buffer should be close to the desired mobile phase pH. The buffer must be compatible with the solvent that is being used in the mobile phase, mostly with the common organic solvents mentioned above, acetonitrile, methanol, and isopropanol. If UV absorption spectroscopy is used for detection, the buffer should have low absorption at the chosen wavelength. If mass spectrometry (MS) is used for detection, the buffer must be compatible with the MS instrument. Some buffers, such as those containing phosphate salts, cannot be used with the MS detectors, as they are not volatile, and they suppress the analytes ionization, making them undetected by MS. Charged analytes can also be separated by ion interaction reverse-phase chromatography.
Sources: en.wikipedia.org
=== Dietary sources === Aspartic acid is not an essential amino acid, which means that it can be synthesized from central metabolic pathway intermediates in humans, and does not need to be present in the diet. In eukaryotic cells, roughly 1 in 20 amino acids incorporated into a protein is an aspartic acid, and accordingly almost any source of dietary protein will include aspartic acid. Additionally, aspartic acid is found in:
=== An overview of the GW model === Greenwood and Williamson in 1966 (GW) proposed a theory of elastic contact mechanics of rough surfaces which is today the foundation of many theories in tribology (friction, adhesion, thermal and electrical conductance, wear, etc.). They considered the contact between a smooth rigid plane and a nominally flat deformable rough surface covered with round tip asperities of the same radius R. Their theory assumes that the deformation of each asperity is independent of that of its neighbours and is described by the Hertz model. The heights of asperities have a random distribution. The probability that asperity height is between
=== "Moonlighting" === In addition to its intracellular role as the major actin-sequestering molecule in cells of many multicellular animals, thymosin β4 shows a remarkably diverse range of effects when present in the fluid surrounding animal tissue cells. Taken together, these effects suggest that thymosin has a general role in tissue regeneration. This has suggested a variety of possible therapeutic applications, and several have now been extended to animal models and human clinical trials. It is considered unlikely that thymosin β4 exerts all these effects via intracellular sequestration of G-actin. This would require its uptake by cells, and moreover, in most cases the cells affected already have substantial intracellular concentrations. The diverse activities related to tissue repair may depend on interactions with receptors quite distinct from actin and possessing extracellular ligand-binding domains. Such multi-tasking by, or "partner promiscuity" of, proteins has been referred to as protein moonlighting. Proteins such as thymosins which lack stable folded structure in aqueous solution, are known as intrinsically unstructured proteins (IUPs). Because IUPs acquire specific folded structures only on binding to their partner proteins, they offer special possibilities for interaction with multiple partners. A candidate extracellular receptor of high affinity for thymosin β4 is the β subunit of cell surface-located ATP synthase, which would allow extracellular thymosin to signal via a purinergic receptor.
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Sources: en.wikipedia.org
== Moving wire IRMS == Moving wire IRMS is useful for analyzing carbon-13 ratios of compounds in a solution, such as after purification by liquid chromatography. The solution (or outflow from the chromatography) is dried onto a nickel or stainless steel wire. After the residue is deposited on the wire, it enters a furnace where the sample is converted to CO2 and water by combustion. The gas stream finally enters a capillary, is dried, ionized, and analyzed. This process allows a mixture of compounds to be purified and analyzed continuously, which can decrease the analysis time by a factor of four. Moving wire IRMS is quite sensitive, and samples containing as little as 1 nanomole of carbon can yield precise (within 1‰) results.
The Black Mesa Research Facility (also simply called Black Mesa) is a fictional large underground laboratory complex that serves as the primary setting for the video game Half-Life and its expansions, as well as its unofficial remake, Black Mesa. It also features in the wider Half-Life universe, including the Portal series. Located in the New Mexico desert in a decommissioned Cold War missile site, it is the former employer of Half-Life's theoretical physicist protagonist, Gordon Freeman, and a competitor of Aperture Science. While the facility ostensibly conducts military-industrial research, its secret experiments into teleportation have caused it to make contact with the alien world of Xen, and its scientists covertly study its life-forms and materials. In a catastrophic event known as the "Black Mesa Incident", an "anti-mass spectrometer" experiment conducted on Xen matter causes a Resonance Cascade disaster that allows aliens to invade Earth, and is the catalyst for the events of the series. Half-Life was critically acclaimed for its storytelling and level design. At the time, the integration of narrative into gameplay through scripted sequences and NPCs instead of through cutscenes was considered groundbreaking for a first-person shooter.
==== Small interfering RNA (siRNA) ==== siRNAs are small RNA molecules that induce the sequence-specific degradation of other RNAs. siRNA treatment can function similar to traditional gene therapy by destroying the mRNA products of particular genes, and therefore preventing the expression of those genes. A 2012 study found that targeting TERC with an siRNA reduced telomerase activity by more than 50% and resulted in decreased viability of immortal cancer cells. Treatment with both the siRNA and radiation caused a greater reduction in tumor size in mice than treatment with radiation alone, suggesting that targeting telomerase could be a way to increase the efficacy of radiation in treating radiation-resistant tumors.
At the time, low-potency creatine supplements were available in Britain, but creatine supplements designed for strength enhancement were not commercially available until 1993 when the company Experimental and Applied Sciences (EAS) introduced the compound to the sports nutrition market under the name Phosphagen. In 1996, researchers found that carbohydrate consumption augments the effects of creatine supplementation on skeletal muscle creatine accumulation.
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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.
Major regulatory agencies have not approved it for any indication. Some countries permit it only under prescription frameworks, while others classify it as a controlled substance.