MC1R 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.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Melanotan II is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous peptide involved in pigment production. The analogue carries a lactam bridge that constrains the ring and slows enzymatic breakdown relative to the native hormone. In research literature it appears under several abbreviations, and naming conventions are not fully standardized. Published descriptions usually place it within the broader melanocortin agonist family.
Receptor binding at MC1R on melanocytes raises intracellular cyclic AMP and increases expression of tyrosinase and related enzymes. The downstream result is greater synthesis of eumelanin, the dark pigment, without ultraviolet exposure acting as the trigger. The compound is not selective, however, and also engages MC3R, MC4R and MC5R, which are expressed in the central nervous system and elsewhere. That lack of selectivity is the explanation usually offered for effects reported outside pigmentation, including appetite suppression and nausea. Selectivity remains a central theme in comparative studies of related peptides.
Melanotan II holds no marketing authorisation from the Food and Drug Administration, the European Medicines Agency, the UK Medicines and Healthcare products Regulatory Agency or Australia's Therapeutic Goods Administration. Products sold under that name are treated as unapproved new drugs, and their sale or import is prohibited in several jurisdictions. Other countries classify the peptide as a prescription-only medicine or place it among controlled substances, so the legal position changes with the destination market. No pharmacopoeial monograph supplies an official specification, because the material is not a licensed pharmaceutical. Consequently, products offered online are not manufactured to a shared public standard.
The peer-reviewed record is dominated by small early-phase studies, case reports and pharmacovigilance summaries rather than large randomised trials. Papers typically examine tanning response, receptor selectivity or patterns of reported adverse events. Many note that participants obtained the peptide outside a clinical setting, which limits verification of composition and administered amount. Reported events vary widely, and causality is frequently unclear because the identity and purity of self-sourced material are unknown. Open questions include whether repeated melanocortin receptor stimulation produces cumulative effects, and how often label claims match actual content.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Melanocortin receptor agonist |
| Molecular formula | C50H69N15O9 | Neutral form, mass near 1024.2 g/mol |
| Primary targets | MC1R, MC3R, MC4R, MC5R | Binding is non-selective across subtypes |
| Related compounds | Alpha-MSH, melanotan I, afamelanotide | Structurally or functionally related peptides |
| Common abbreviations | MT-II, MT-2 | Naming in the literature is not uniform |
Melanotan II is a synthetic peptide analog modeled on alpha-melanocyte-stimulating hormone, a naturally occurring signaling peptide involved in pigmentation. Its structure is a cyclic heptapeptide containing two non-natural substitutions, norleucine at position four and D-phenylalanine at position seven. These modifications resist enzymatic breakdown and extend the molecule's activity relative to the native hormone. The compound binds melanocortin receptors and is studied mainly as a pharmacological tool rather than a therapeutic product. It has never received approval as a medicine in any major jurisdiction.
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.
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.
The county is named after the ancient Welsh Kingdom of Powys, which in the sixth century AD included the northern two-thirds of the area as well as most of Shropshire, Herefordshire and adjacent areas now in England, and came to an end when it was occupied by Llywelyn ap Gruffudd of Gwynedd during the 1260s. The uplands retain evidence of occupation from long before the Kingdom of Powys, and before the Romans, who built roads and forts across the area. There are 1130 identified burial mounds within the county, of varying styles and ages, dating from 4000 BC to 1000 BC, most of them belonging to the Bronze Age. Of these, 339 are scheduled monuments. Standing stones, most again dating to the Bronze Age, also occur in large numbers, 276 being found across the county, of which 92 are scheduled. From the Iron Age, the county has 90 scheduled hillforts and a further 54 enclosures and settlement sites. Powys is served by the Cambrian Line and Heart of Wales line which offer connections to major towns and cities such as Swansea, Wrexham, Shrewsbury, Birmingham, Wolverhampton, Manchester, Cardiff, Aberystwyth, London and Telford. The county used to be served by key railways such as the Mid-Wales Railway, Oswestry and Newtown Railway, Tanat Valley Light Railway, Llanfyllin Branch, Leominster and Kington Railway, Swansea Vale Railway and the Hereford, Hay and Brecon Railway, all of which offered connections to South Wales, Hereford, Oswestry, North Wales and West Wales but have all since closed.
=== Museums === Abbey House Museum, Leeds Armley Mills Industrial Museum, Leeds Bagshaw Museum, Batley Bankfield Museum, Halifax Bradford Industrial Museum, Eccleshill/Fagley, Bradford Brontë Parsonage Museum, Haworth Colne Valley Museum, Golcar, Huddersfield Eureka, Halifax Leeds City Museum, Leeds National Coal Mining Museum for England Overton, Wakefield National Media Museum, Bradford Pennine Farm Museum, Ripponden, Halifax Pontefract Museum Royal Armouries Museum, Leeds Thackray Museum, Leeds The Hepworth Wakefield Thwaite Mills, Leeds Tolson Museum, Dalton, Huddersfield Wakefield Museum, Wakefield West Yorkshire Folk Museum, Shibden Hall, Halifax Yorkshire Sculpture Park, West Bretton, Wakefield
== Structure == Solid anthranilic acid crystallizes as a 1:1 mixture of the amino-carboxylic acid and the zwitterionic ammonium carboxylate forms. It is triboluminescent. Above 81 °C (178 °F; 354 K), it converts from monoclinic P21 polymorph to an orthorhombic form with space group Pbca, which is not triboluminescent. A non-triboluminescent monoclinic phase with similar structure is also known.
Sources: en.wikipedia.org
==== Adsorption ==== A straightforward method for reversible immobilization, involving the enzymes being adsorbed or attached physically onto a support substance. Adsorption can take place through weak non-specific forces, such as van der waals, hydrogen bonds, and hydrophobic interactions, whereas in ionic bonding the enzymes are bound through salt linkages. Adsorption on glass, alginate beads or matrix: Enzyme is attached to the outside of an inert material. In general, this method is the slowest among those listed here. As adsorption is not a chemical reaction, the active site of the immobilized enzyme may be blocked by the matrix or bead, greatly reducing the activity of the enzyme.
== Prediction == There are many situations where prediction of partition coefficients prior to experimental measurement is useful. For example, tens of thousands of industrially manufactured chemicals are in common use, but only a small fraction have undergone rigorous toxicological evaluation. Hence there is a need to prioritize the remainder for testing. QSAR equations, which in turn are based on calculated partition coefficients, can be used to provide toxicity estimates. Calculated partition coefficients are also widely used in drug discovery to optimize screening libraries and to predict druglikeness of designed drug candidates before they are synthesized. As discussed in more detail below, estimates of partition coefficients can be made using a variety of methods, including fragment-based, atom-based, and knowledge-based that rely solely on knowledge of the structure of the chemical. Other prediction methods rely on other experimental measurements such as solubility. The methods also differ in accuracy and whether they can be applied to all molecules, or only ones similar to molecules already studied.
The chemical model will include values of the protonation constants of the ligand, which will have been determined in separate experiments, a value for log Kw and estimates of the unknown stability constants of the complexes formed. These estimates are necessary because the calculation uses a non-linear least-squares algorithm. The estimates are usually obtained by reference to a chemically similar system. The stability constant databases can be very useful in finding published stability constant values for related complexes. In some simple cases the calculations can be done in a spreadsheet. Otherwise, the calculations are performed with the aid of a general-purpose computer programs. The most frequently used programs are:
Sources: en.wikipedia.org
Unlike the similarly named tacrolimus, sirolimus is not a calcineurin inhibitor, but it has a similar suppressive effect on the immune system. Sirolimus inhibits IL-2 and other cytokine receptor-dependent signal transduction mechanisms, via action on mTOR (mammalian Target Of Rapamycin, rapamycin being another name for sirolimus), and thereby blocks activation of T and B cells. Ciclosporin and tacrolimus inhibit the secretion of IL-2, by inhibiting calcineurin. The mode of action of sirolimus is to bind the cytosolic protein FK-binding protein 12 (FKBP12) like tacrolimus. Unlike the tacrolimus-FKBP12 complex, which inhibits calcineurin (PP2B), the sirolimus-FKBP12 complex inhibits the mTOR pathway by directly binding to mTOR Complex 1 (mTORC1). mTOR has also been called FRAP (FKBP-rapamycin-associated protein), RAFT (rapamycin and FKBP target), RAPT1, or SEP. The earlier names FRAP and RAFT were coined to reflect the fact that sirolimus must bind FKBP12 first, and only the FKBP12-sirolimus complex can bind mTOR. However, mTOR is now the widely accepted name, since Tor was first discovered via genetic and molecular studies of sirolimus-resistant mutants of Saccharomyces cerevisiae that identified FKBP12, Tor1, and Tor2 as the targets of sirolimus and provided robust support that the FKBP12-sirolimus complex binds to and inhibits Tor1 and Tor2.
=== Powdered egg whites === Egg white can be dried alone for better foaming. The result is egg white powder. The ingredient called egg white protein is virtually identical to egg white powder, as no additional step is employed to separate the protein in egg white from other components before drying. Dried egg white products often have their foaming ability compromised by the inadvertent inclusion of egg yolk. Adding phospholipase A2 appears to break down the contaminant and restore the foaming power.
As demanded by the Allied Commission, the German police escorted Polish actors but they ignored the attackers. In Bischofsburg (Biskupiec), a pogrom against Poles was organised, which prompted the creation of a special commission to find the perpetrators. The Allensteiner Zeitung newspaper called on its readers to remain calm and to cease pogroms against Poles and pointed out that they could lead to postponing the plebiscite, which would go against German interests. Italian forces were sent to Lötzen (Giżycko), according to Minakowski, to protect the Poles after a pogrom had occurred on 17 April. In May, several attacks on Poles were reported in Osterode (Ostróda) and included attacks on coworkers of the Masurian Committee.
saturation hybridization An in vitro nucleic acid hybridization reaction in which one polynucleotide component (either DNA or RNA) is supplied in great excess relative to the other, causing all complementary sequences in the other polynucleotide to pair with the excess sequences and form hybrid duplex molecules.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide and a non-selective melanocortin receptor agonist. Structurally it is modelled on alpha-melanocyte-stimulating hormone, a peptide that occurs naturally in the body.
Activation of MC1R increases pigment synthesis independently of ultraviolet exposure, which is the mechanism usually cited for darkening without sun exposure. Ultraviolet light still influences skin response through separate biological pathways.
Because the peptide binds several melanocortin receptor subtypes, its effects are not confined to pigmentation. This complicates interpretation of both intended and unintended outcomes reported in studies.
Regulatory treatment varies by country. In the United States, the European Union and Australia it is an unapproved drug and its sale is restricted, while some other jurisdictions list it as prescription-only or controlled. The applicable rules depend on the country of import.