If you have been reading about melanocortin receptor and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-05-15. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
| 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 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.
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.
The Western blots were first stained with Ponceau and then incubated with IgG antibodies against hGH and subsequently treated with α-mIgG HRP and α-hIgG 647 for visualisation. In the hIgG-hGH conjugate Western blot (nonreducing conditions), two separate bands with different molecular weights are visible after immunodetection. These can be contributed to the formation of mono- and bi-conjugated hGH to hIgG.
The newer drugs have a better bioavailability as they are not charged and have a non-ionic interaction to the S1 pocket. Rivaroxaban During the SAR development of rivaroxaban, researchers realized that adding a 5-chlorothiophene-2-carboxamide group to the oxazolidonine core could increase the potency by 200 fold, which had previously been too weak for medical use. In addition to this discovery, a clear preference for the (S)-configuration was confirmed. This compound had a promising pharmacokinetical profile and did not contain a highly basic amidine group, but that had previously been considered important for the interaction with the S1 pocket. These findings lead to extensive SAR (structure-activity relationship) researches. During the SAR testing, R1 was defined as the most important group for potency. Pyrrolidinone was the first R1 functional group to significantly increase the potency but further researches revealed even higher potency with a morpholinone group instead. Groups R2 and R3 had hydrogen or fluorine attached and it was quickly assessed that having hydrogen resulted in highest potency. Groups R2 and R3 were then substituted for various groups, which were all less potent than the hydrogen, so hydrogen was the final result. As the chlorothiophene moiety had an inadequate water solubility, substituting it with another group was attempted but was unsuccessful. The chlorothiophene moiety binds to Tyr-228 at the bottom of the S1 pocket, making it a key factor regarding binding to FXa. Rivaroxaban has both high affinity and good bioavailability.
== Versus point of zero charge == The terms isoelectric point (IEP) and point of zero charge (PZC) are often used interchangeably, although under certain circumstances, it may be productive to make the distinction. In systems in which H+/OH− are the interface potential-determining ions, the point of zero charge is given in terms of pH. The pH at which the surface exhibits a neutral net electrical charge is the point of zero charge at the surface. Electrokinetic phenomena generally measure zeta potential, and a zero zeta potential is interpreted as the point of zero net charge at the shear plane. This is termed the isoelectric point. Thus, the isoelectric point is the value of pH at which the colloidal particle remains stationary in an electrical field. The isoelectric point is expected to be somewhat different from the point of zero charge at the particle surface, but this difference is often ignored in practice for so-called pristine surfaces, i.e., surfaces with no specifically adsorbed positive or negative charges. In this context, specific adsorption is understood as adsorption occurring in a Stern layer or chemisorption. Thus, point of zero charge at the surface is taken as equal to isoelectric point in the absence of specific adsorption on that surface. According to Jolivet, in the absence of positive or negative charges, the surface is best described by the point of zero charge. If positive and negative charges are both present in equal amounts, then this is the isoelectric point.
Sources: en.wikipedia.org
== Method == A model resonance ionization mass spectrometry (RIMS) set-up consists of a laser system (consisting of multiple lasers), sample from which the atoms are derived, and a suitable mass spectrometer which mass-selectively detects the photo ions created from resonance. In resonant ionization, atoms or molecules from ground state are excited to higher energy states by the resonant absorption of photons to produce ions. These ions are then monitored by appropriate detectors. In order to ensure a highly-efficient sensitivity and process saturation, the atomic or molecular beam must be formed from the ground state, the atoms should be efficiently excited and ionized, and each atom should be converted by the photon field of a short-timed pulsed laser to produce a positive ion and a valence electron. In a basic RIS process, a pulsed laser beam produces photons of the right energy in order to excite an atom initially in its ground state, a, to an excited level, b. During the laser pulse, the ion population of state b increases at the expense of that of state a. After a few minutes, the rate of stimulated emission from the excited state will equal rate of production so that the system is in equilibrium as long as the laser intensity is kept sufficiently high during a pulse. This high laser intensity translates into a photon fluence (photons per unit of beam area) large enough so that a necessary condition for the saturation of the RIS process has been met.
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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 a non-selective melanocortin receptor agonist. Structurally it is modelled on alpha-melanocyte-stimulating hormone, a peptide that occurs naturally in the body.