Everything below concerns cyclic heptapeptide. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Updated 2025-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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 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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Free base; salt forms add to total mass |
| Molecular mass | About 1024 daltons | Calculated for the free base |
| Structural class | Cyclic heptapeptide | Contains D-phenylalanine and norleucine |
| Parent hormone | Alpha-melanocyte-stimulating hormone | Endogenous tridecapeptide of 13 residues |
| Receptor profile | Non-selective melanocortin agonist | Interacts with MC1R, MC3R, MC4R and MC5R |
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.
=== Thorium-231 === 231Th has 141 neutrons. It is the decay product of uranium-235. It is found in very small amounts on the earth and has a half-life of 25.52 hours. When it decays, it emits a beta ray and forms protactinium-231, with a decay energy of 0.39 MeV.
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Sources: en.wikipedia.org
== Stable isotope analysis == Stable isotope biogeochemistry uses variations in isotopic signatures and relates them to biogeochemical processes. The science is based on the preferential fractionation of lighter or heavier isotopes, which results in enriched and depleted isotopic signatures compared to a standard value. Essential elements for life such as carbon, nitrogen, oxygen, and sulfur are the primary stable isotope systems used to interrogate archeological discoveries. Isotopic signatures from multiple systems are typically used in tandem to create a comprehensive understanding of the analyzed material. These systems are most commonly used to trace the geographic origin of archaeological remains and investigate the diets, mobility, and cultural practices of ancient humans.
On May 20, 2008, Merck settled for $58 million with 30 states alleging that Merck engaged in deceptive marketing tactics to promote Vioxx. All its new television pain-advertisements must be vetted by the Food and Drug Administration and changed or delayed upon request until 2018.
=== Comparisons between eukaryotes and prokaryotes === Protein phosphorylation is a reversible post-translational modification of proteins. In eukaryotes, protein phosphorylation functions in cell signaling, gene expression, and differentiation. It is also involved in DNA replication during the cell cycle, and the mechanisms that cope with stress-induced replication blocks. Compared to eukaryotes, prokaryotes use Hanks-type kinases and phosphatases for signal transduction. Whether or not the phosphorylation of proteins in bacteria can also regulate processes like DNA repair or replication still remains unclear. Compared to the protein phosphorylation of prokaryotes, studies of protein phosphorylation in eukaryotes from yeast to human cells have been rather extensive. It is known that eukaryotes rely on the phosphorylation of the hydroxyl group on the side chains of serine, threonine, and tyrosine for cell signaling. These are the main regulatory post-translational modifications in eukaryotic cells but the protein phosphorylation of prokaryotes are less intensely studied. While serine, threonine, and tyrosine are phosphorylated in eukaryotes, histidine and aspartate is phosphorylated in prokaryotes and eukaryotes. In bacteria, histidine phosphorylation occurs in the phosphoenolpyruvate-dependent phosphotransferase systems (PTSs), which are involved in the process of internalization as well as the phosphorylation of sugars. Protein phosphorylation by protein kinase was first shown in E.
Sources: en.wikipedia.org
No regulatory agency has authorised melanotan-2 as a medicine for any indication. It circulates mainly as a research chemical or through unregulated channels. As a result, identity, purity and content are not independently guaranteed.
Melanotan-1, also called afamelanotide, is a linear analogue with greater selectivity for MC1R and has received approval in some jurisdictions for a specific photosensitivity disorder. Melanotan-2 is cyclic, less selective, and reaches central receptors more readily. The two are often confused in online discussion despite different pharmacology and regulatory status.
Alpha-MSH is an endogenous tridecapeptide derived from pro-opiomelanocortin. Melanotan-2 reproduces its core receptor-binding sequence inside a shortened, stabilised ring. The result is a molecule with a longer effective half-life and higher potency than the parent hormone.
It is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, containing seven amino acids with a lactam ring and a D-configured phenylalanine residue. It is supplied as a lyophilised powder for laboratory research.