MC1R comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-06-24. 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 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.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its sequence incorporates modified residues that increase potency and extend biological activity relative to the native hormone. The compound binds receptors of the melanocortin family and is examined mainly in laboratory research. It does not occur naturally and exists only as a manufactured chemical entity produced by solid-phase synthesis.
The peptide was developed during the 1980s by researchers investigating melanocortin signalling and skin pigmentation pathways. Early work focused on analogues of alpha-melanocyte-stimulating hormone that would resist enzymatic breakdown more effectively than the parent molecule. Melanotan-2 emerged from that programme as a shortened, cyclised variant. Reports describing its synthesis and receptor activity later appeared in the scientific literature. Commercial availability grew through unregulated channels rather than through pharmaceutical approval.
| 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, 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.
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
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 II is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its structure substitutes a lactam bridge between side chains to increase stability relative to the native hormone. The compound is also known by the shorthand MT-II and by several non-proprietary synonyms used in research catalogues. It is not an approved therapeutic product in any major jurisdiction; material sold under this name is typically offered as a laboratory reagent rather than as a medicine.
Activity is attributed to agonism at melanocortin receptors, particularly MC1R and MC4R. Activation of MC1R on melanocytes increases melanin synthesis, which underlies the reported tanning effect. MC4R engagement in the central nervous system is linked to appetite suppression and to effects on sexual arousal reported in early clinical studies. Those studies were small and were not designed to establish efficacy or long-term safety. Receptor selectivity among the melanocortin subtypes is not absolute, which complicates attribution of any effect to a single pathway.
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.
Melanotan-2 is a synthetic peptide designed as an analog of alpha-melanocyte-stimulating hormone, a signaling molecule produced in the pituitary and skin. Its structure is a linear chain of seven amino acids that folds into a ring through an internal lactam bridge joining two side chains. The compound is sometimes written as MT-II or MEL-2 in informal and commercial contexts. It belongs to the melanocortin peptide family, a group of short signaling molecules that share a conserved core sequence recognized by melanocortin receptors.
Two structural changes distinguish the synthetic peptide from the natural hormone. A norleucine residue replaces methionine at one position, and a D-configured phenylalanine replaces the natural L-form at another. Both substitutions slow enzymatic breakdown, which extends the molecule's persistence relative to the parent hormone. The lactam bridge further constrains the backbone into a stable conformation. These features are standard design strategies in peptide chemistry and are not unique to this compound; they appear across many research peptides built for improved stability.
The saboteur is eventually revealed to be a bird pecking at the console's keyboard, which sends GLaDOS into a panic when she recognizes it as the one who tried to eat her during her time as a potato. ATLAS and P-body manage to shoo away the bird, earning a rare compliment from GLaDOS before she notices eggs in its nest. Instead of having them smashed, GLaDOS has the eggs taken to her chamber so that she can raise the baby birds to be her own little "killing machines". According to GLaDOS, ATLAS and P-body were created for the Cooperative Testing Initiative and were supposed to phase out human testing after Chell escaped with Wheatley. However, she never got around to using them for testing. In the Portal 2 singleplayer campaign, Wheatley finds both ATLAS and P-body in storage and decided to kill both Chell and GLaDOS and use them instead. They later appear when Chell is granted liberty by GLaDOS. Originally, the co-op player characters would be Chell (the single player character), and Mel, another human test subject. This concept was cut when playtesting showed that co-op characters would die a lot. The humans were replaced with infinite respawning robots. During the early phases of Portal 2, ATLAS and P-body's concept showed more of a Westworld feel.
18 Poems, The Sunday Referee; Parton Bookshop, 1934 Portrait of the Artist as a Young Dog, London: Dent, 1940 Deaths and Entrances, London: Dent, 1946 A Child's Christmas in Wales, New Directions, 1955 The Collected Poems of Dylan Thomas: The New Centenary Edition. Ed. with Introduction and annotations by John Goodby. London: Weidenfeld & Nicolson, 2014 The Notebook Poems 1930–34, ed. Ralph Maud. London: Dent, 1989 Dylan Thomas: The Broadcasts, ed. Ralph Maud. London: Dent, 1991 Dylan Thomas: The Filmscripts, ed. John Ackerman. London: Dent, 1995 Dylan Thomas: Early Prose Writings, ed. Walford Davies. London: Dent, 1971 Collected Stories, ed. Walford Davies. London: Dent, 1983 Under Milk Wood: A Play for Voices, ed. Walford Davies and Ralph Maud. London: Dent, 1995 On the Air with Dylan Thomas: The Broadcasts, ed. R. Maud. New York: New Directions, 1991
== Physiological distribution == Lipases are involved in diverse biological processes which range from routine metabolism of dietary triglycerides to cell signaling and inflammation. Thus, some lipase activities are confined to specific compartments within cells while others work in extracellular spaces.
Sources: en.wikipedia.org
TVLine reported in late April that a new gladiator would be added to Olivia Pope & Associates, and the person would be a guest star. It was also announced on July 7, 2015, that Cornelius Smith Jr., who had a guest role in season four playing activist Marcus Walker, will be returning as a series regular for the fifth season, but will not appear until later in the fall. On August 24, 2015, it was announced that actress Mia Maestro would be recurring during the fifth season, but the specifics of her role were not revealed. Julie Claire was announced on September 1, 2015, to have joined the cast in a guest role. It was announced on February 4, 2016, that Ricardo Chavira would join the show in a recurring role, and would first appear in the eleventh episode. Annabeth Gish was announced on February 8, 2016, to have been cast in a recurring role. The Hollywood Reporter announced on February 18, 2016, that Joe Morton who plays Rowan "Eli" Pope had been promoted to a series regular, and was credited as a regular cast member for the first time in the twelfth episode.
=== Judaism === Israeli prime minister Benjamin Netanyahu referenced the Torah and compared Iran to the ancient biblical enemy of the Amalekites, stating "We read in this week's Torah portion, 'Remember what Amalek did to you.' We remember—and we act." The Council on American–Islamic Relations condemned Netanyahu for "once again using the biblical story of Amalek—which claims that God commanded the Israelites to murder every man, woman, child and animal in a pagan nation that attacked them—to justify Israel's mass murder of civilians in Iran, just as it did in Gaza."
== References == Pathology Outline, Fallopian Tubes Ogawa K, Johansson SL, Cohen SM (October 1999). "Immunohistochemical analysis of uroplakins, urothelial specific proteins, in ovarian Brenner tumors, normal tissues, and benign and neoplastic lesions of the female genital tract". Am. J. Pathol. 155 (4): 1047–50. doi:10.1016/S0002-9440(10)65206-6. PMC 1867018. PMID 10514386. Wrong Diagnosis.com, Brenner tumors
Sources: en.wikipedia.org
=== Brittleness === Most salts are very brittle. Once they reach the limit of their strength, they cannot deform malleably, because the strict alignment of positive and negative ions must be maintained. Instead the material undergoes fracture via cleavage. As the temperature is elevated (usually close to the melting point) a ductile–brittle transition occurs, and plastic flow becomes possible by the motion of dislocations.
Almost all proteins that are destined to the secretory pathway have a sequence consisting of 5-30 hydrophobic amino acids on the N-terminus, which is commonly referred to as the signal peptide, signal sequence or leader peptide. Signal peptides form alpha-helical structures. Proteins that contain such signals are destined for either extra-cellular secretion, the plasma membrane, the lumen or membrane of either the (ER), Golgi or endosomes. Certain membrane-bound proteins are targeted to the secretory pathway by their first transmembrane domain, which resembles a typical signal peptide. In prokaryotes, signal peptides direct the newly synthesized protein to the SecYEG protein-conducting channel, which is present in the plasma membrane. A homologous system exists in eukaryotes, where the signal peptide directs the newly synthesized protein to the Sec61 channel, which shares structural and sequence similarity with SecYEG, but is present in the endoplasmic reticulum. Both the SecYEG and Sec61 channels are commonly referred to as the translocon, and transit through this channel is known as translocation. While secreted proteins are threaded through the channel, transmembrane domains may diffuse across a lateral gate in the translocon to partition into the surrounding membrane.
Confluent and reticulated papillomatosis (confluent and reticulated papillomatosis of Gougerot and Carteaud, familial cutaneous papillomatosis, familial occurrence of confluent and reticulated papillomatosis) Digitate dermatosis Drug-induced keratoderma Exfoliative dermatitis (dermatitis exfoliativa, erythroderma, red man syndrome) Florid cutaneous papillomatosis Granular parakeratosis (axillary granular parakeratosis, intertriginous granular parakeratosis) Keratolysis exfoliativa (lamellar dyshidrosis, recurrent focal palmar peeling, recurrent palmar peeling) Keratosis punctata of the palmar creases (hyperkeratosis penetrans, hyperkeratosis punctata, keratodermia punctata, keratosis punctata, keratotic pits of the palmar creases, lenticular atrophia of the palmar creases, punctate keratosis of the palmar creases) Meesmann corneal dystrophy Paraneoplastic keratoderma Pityriasis rosea (pityriasis rosea Gibert) Pityriasis rubra pilaris (Devergie's disease, lichen ruber acuminatus, lichen ruber pilaris) Pure hair-nail type ectodermal dysplasia Small plaque parapsoriasis (chronic superficial dermatitis) Tripe palms Xanthoerythrodermia perstans
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 and an analogue of alpha-melanocyte-stimulating hormone. The molecule is produced by chemical synthesis rather than extracted from a biological source.