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 2026-06-10. Anything still debated is marked as such rather than presented as settled.
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.
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.
| 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 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.
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.
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.
Nitriles are susceptible to hydrogenation over diverse metal catalysts. The reaction can afford either the primary amine (RCH2NH2) or the tertiary amine ((RCH2)3N), depending on conditions. In conventional organic reductions, nitrile is reduced by treatment with lithium aluminium hydride to the amine. Reduction to the imine followed by hydrolysis to the aldehyde takes place in the Stephen aldehyde synthesis, which uses stannous chloride in acid.
It is a measurement of the contribution of a genotype to the next generation where a value of 1 would be completely selected against and make no contribution and 0 is not selected against at all. This definition of neutral mutation has been criticized due to the fact that very large effective population sizes can make mutations with small selection coefficients appear non neutral. Additionally, mutations with high selection coefficients can appear neutral in very small populations. The testable hypothesis of Kimura and others showed that polymorphism within species are approximately that which would be expected in a neutral evolutionary model. For many molecular biology approaches, as opposed to mathematical genetics, neutral mutations are generally assumed to be those mutations that cause no appreciable effect on gene function. This simplification eliminates the effect of minor allelic differences in fitness and avoids problems when a selection has only a minor effect. Early convincing evidence of this definition of neutral mutation was shown through the lower mutational rates in functionally important parts of genes such as cytochrome c versus less important parts and the functionally interchangeable nature of mammalian cytochrome c in in-vitro studies. Nonfunctional pseudogenes provide more evidence for the role of neutral mutations in evolution. The rates of mutation in mammalian globin pseudogenes has been shown to be much higher than rates in functional genes.
=== Boers retreat === The set-piece period of the war now largely gave way to a guerrilla war, but one final operation remained. President Kruger and what remained of the Transvaal government had retreated to eastern Transvaal. Roberts, joined by troops from Natal under Buller, advanced against them, and broke their last defensive position at Bergendal on 26 August. As Roberts and Buller followed up along the railway line to Komatipoort, Kruger sought asylum in Portuguese East Africa (modern Mozambique). Some dispirited Boers did likewise, and the British gathered up much war material. However, the core of the Boer fighters under Botha easily broke back through the Drakensberg Mountains into the Transvaal highveld after riding north through the bushveld. As Roberts's army occupied Pretoria, the Boer fighters in the Orange Free State retreated into the Brandwater Basin, a fertile area in the south-east of the Republic. This offered only temporary sanctuary, as the mountain passes leading to it could be occupied by the British, trapping the Boers. A force under General Archibald Hunter set out from Bloemfontein to achieve this in July 1900. The hard core of the Free State Boers under De Wet, accompanied by President Steyn, left the basin early. Those remaining fell into confusion and most failed to break out before Hunter trapped them.
== Structural aspects == Intrinsically disordered proteins adapt a dynamic range of rapidly interchanging conformations in vivo according to the cell's conditions, creating a structural or conformational ensemble. Their structures are strongly function-related. Few proteins are fully disordered in their native state. Disorder is mostly found in intrinsically disordered regions (IDRs) within an otherwise well-structured protein. The term intrinsically disordered protein (IDP) therefore includes proteins that contain IDRs as well as fully disordered proteins. The existence and kind of protein disorder is encoded in its amino acid sequence. In general, IDPs are characterized by a low content of bulky hydrophobic amino acids and a high proportion of polar and charged amino acids, usually referred to as low hydrophobicity. This property leads to good interactions with water. Furthermore, high net charges promote disorder because of electrostatic repulsion resulting from equally charged residues. Thus disordered sequences cannot sufficiently bury a hydrophobic core to fold into stable globular proteins. In some cases, hydrophobic clusters in disordered sequences provide the clues for identifying the regions that undergo coupled folding and binding (refer to biological roles). Many disordered proteins reveal regions without any regular secondary structure. These regions can be termed as flexible, compared to structured loops. While the latter are rigid and contain only one set of Ramachandran angles, IDPs involve multiple sets of angles.
=== Fraud convictions === From 2017 to 2019, Cochran operated a $2.5 million Ponzi scheme, defrauding investors under the guise of a government contracting business. She persuaded at least 11 individuals to invest in her companies, Technology Management Solutions and Tactical Solutions Group, by falsely claiming she had lucrative government contracts. Instead of investing the funds, Cochran used the money for personal expenses, including purchasing real estate, jewelry, and a 1965 Shelby Cobra. She also used funds from new investors to pay partial returns to earlier investors, a hallmark of Ponzi schemes. One investor alone lost over $500,000 due to her fraudulent activities. Cochran pleaded guilty to wire fraud and money laundering on September 21, 2020, and was sentenced to 135 months in federal prison. She was also ordered to pay $2.5 million in restitution and forfeit assets obtained through her scheme.
Sources: en.wikipedia.org
=== Cell signaling and cell communication === Neither sponges nor the placozoan Trichoplax adhaerens appear to be equipped with neuron synapses, however they both possess several factors related to the same synaptic function. Therefore, it is likely that central features involved in synaptic transmission arose early in metazoan evolution, most likely around the time that much of the life on Earth was transitioning to multicellularity. It was found that the Munc18/syntaxin 1 complex could be an important component for the production of the SNARE protein. The secretion of SNARE protein from synaptic vesicles is believed to be critical for neuronal communication. The Munc18/syntaxin 1 complex found in M. brevicollis is both structurally and functionally similar to the metazoan complex. This suggests that it constitutes an important step in the reaction pathway toward SNARE assembly. It is believed that the common ancestor of choanoflagellates and metazoans used this primordial secretion machinery as a precursor to synaptic communication. This mechanism would eventually be used for cell-cell communication in animals.
==== Spontaneous intracranial hypotension ==== Spontaneous intracranial hypotension (SIH) refers to lower than normal CSF volume due to a leak of CSF at the level of the spine. Spontaneous intracranial hypotension (SIH) is an important cause of longstanding headaches. Other symptoms can include nausea, blurred vision, coma, and dementia. SIH is typically secondary to a spontaneous spinal CSF leak. Cranial CSF leaks do not cause SIH. While this symptom can be referred to as intracranial hypotension, the intracranial pressure may be normal, with the underlying issue instead being low CSF volume, in this case a sCSFL may be referred to as CSF hypovolemia.
=== Liver and kidney failure === The drug should be used with caution in those with liver or kidney failure, due to metabolism in the liver (to the active molecule desmetramadol) and elimination by the kidneys.
A chordate ( KOR-dayt) is a bilaterian animal belonging to the phylum Chordata ( kor-DAY-tə). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa: a notochord, a hollow dorsal nerve cord, an endostyle or thyroid, pharyngeal slits, and a post-anal tail. In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in their proteins: cyclophilin-like protein and inner mitochondrial membrane protease ATP23, which are exclusively shared by all vertebrates, tunicates, and cephalochordates. These CSIs provide molecular means to reliably distinguish chordates from all other animals. Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds and mammals), which possess a skull and whose notochords are replaced by a cartilaginous/bony axial endoskeleton (spine); Tunicata or Urochordata (sea squirts, salps, and larvaceans), which only retain the synapomorphies during their larval stage; and Cephalochordata (lancelets), which resemble jawless fish but have no gills or a distinct head. The vertebrates and tunicates compose the clade Olfactores (see diagram under Phylogeny), which is characterized by the presence of an advanced olfactory system and is sister to Cephalochordata. Extinct taxa such as the conodonts are chordates, but their internal placement is less certain.
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.
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.