Research Use Only. The information presented here is for scientific and educational purposes. These compounds are not intended for human consumption, self-administration, or therapeutic use.
Introduction
Melanotan-2 (frequently abbreviated MT-2 or MT-II) is a synthetic cyclic peptide studied as a non-selective agonist of the melanocortin receptor family. It was engineered as a structural analog of alpha-melanocyte-stimulating hormone (alpha-MSH), the endogenous melanocortin peptide that drives pigment-forming signaling in melanocytes. Research interest in the Melanotan-2 mechanism centers on how a compact, conformationally constrained peptide engages receptors such as MC1R, MC3R, and MC4R, and on how that engagement is measured in cell and animal models of melanogenesis (the biochemical production of melanin).
This article reviews the receptor pharmacology and intracellular signaling that define Melanotan-2 in the laboratory literature. The framing throughout is preclinical: how the molecule is built, which receptors it is reported to activate, and what downstream markers investigators track. Nothing here describes human use. Melanotan-2 offered by Rejuven8 Peptides and the wider research peptide catalog is supplied for research use only, not for human consumption.
What Melanotan-2 Is: Structure and Origin
Melanotan-2 is a cyclic heptapeptide. Its design retains the core melanocortin pharmacophore, the His-Phe-Arg-Trp message sequence shared with alpha-MSH, while adding modifications that increase metabolic stability and receptor affinity. A lactam bridge between an aspartic acid residue and a lysine residue locks the backbone into a ring, and the substitution of norleucine (Nle) and D-phenylalanine (D-Phe) reduces enzymatic breakdown relative to the linear native hormone.
A brief history
The melanotropic analog program that produced Melanotan-2 originated at the University of Arizona, where investigators including Mac Hadley and Victor Hruby set out to build alpha-MSH analogs that were more stable and more potent than the parent peptide. The cyclic constraint was a deliberate strategy: by reducing the number of freely rotating bonds, the peptide holds a shape that favors receptor binding.
The identity values below reflect commonly reported laboratory attributes and are provided for comparison only.
| Attribute | Reported value |
|---|---|
| Compound class | Cyclic melanocortin receptor agonist (alpha-MSH analog) |
| Sequence length | 7 residues (cyclic heptapeptide) |
| Molecular formula | C50H69N15O9 |
| Approximate molecular weight | 1024.2 g/mol |
| Structural motif | Lactam-bridged cyclic backbone |
| Primary studied target | MC1R (with MC3R, MC4R, MC5R activity) |
The Melanocortin Receptor Family
Melanocortin signaling runs through five G-protein-coupled receptors, MC1R through MC5R. Each couples to the stimulatory G protein (Gs), so agonist binding raises intracellular cyclic AMP (cAMP). What differs between them is tissue distribution and the physiological process each receptor has been linked to in research.
| Receptor | Principal localization studied | Associated research role |
|---|---|---|
| MC1R | Melanocytes | Melanin synthesis (melanogenesis) |
| MC2R | Adrenal cortex | ACTH-driven steroidogenesis |
| MC3R | Central nervous system | Energy balance and inflammation models |
| MC4R | Central nervous system | Energy homeostasis and feeding-behavior studies |
| MC5R | Exocrine tissue | Secretory gland studies |
Where Melanotan-2 fits
Melanotan-2 is described in the literature as a non-selective agonist: it shows appreciable activity across MC1R, MC3R, MC4R, and MC5R, with negligible action at the ACTH-specific MC2R. For melanogenesis research, MC1R is the receptor of interest, and it is the pathway examined in the next section. This broad receptor coverage is a key reason MT-2 is used as a research probe rather than a receptor-selective tool.
The Melanogenesis Signaling Cascade
When a melanocortin agonist engages MC1R on a melanocyte, the receptor activates adenylyl cyclase through Gs, raising cAMP. Elevated cAMP activates protein kinase A (PKA), which phosphorylates the transcription factor CREB. CREB in turn upregulates MITF (microphthalmia-associated transcription factor), the master regulator of the melanocyte pigment program.
From transcription factor to pigment
MITF drives transcription of the enzymes that build melanin, most notably tyrosinase, together with tyrosinase-related protein 1 (TRP-1) and dopachrome tautomerase (TRP-2/DCT). Tyrosinase catalyzes the rate-limiting steps that convert the amino acid tyrosine into melanin within organelles called melanosomes. A shift in this signaling also favors eumelanin (the darker pigment) over pheomelanin. In cell-based research, investigators commonly quantify this cascade by measuring tyrosinase enzyme activity and total melanin content, frequently using B16 murine melanoma cells or cultured melanocytes as model systems.
Comparative Melanocortin Analogs in Research
Melanotan-2 is one of several melanocortin peptides studied side by side. Comparing their size, geometry, and receptor coverage clarifies why each is used as a distinct research tool. The values below reflect commonly reported laboratory attributes and are provided for comparison only.
| Peptide | Class and structure | Sequence length | Approx. MW (g/mol) | Reported receptor profile |
|---|---|---|---|---|
| Melanotan-2 | Cyclic alpha-MSH analog | 7 (cyclic) | 1024 | Non-selective (MC1R, MC3R, MC4R, MC5R) |
| Melanotan-1 (afamelanotide, NDP-MSH) | Linear alpha-MSH analog | 13 | 1647 | Broad, MC1R-active |
| alpha-MSH | Native melanocortin peptide | 13 | 1665 | Endogenous agonist |
| PT-141 (bremelanotide) | Cyclic MT-2 metabolite | 7 (cyclic) | 1025 | MC1R and MC4R |
The linear thirteen-residue compounds, native alpha-MSH and Melanotan-1, contrast with the compact cyclic heptapeptides Melanotan-2 and PT-141. PT-141 is itself a deaminated metabolite of Melanotan-2, which is why the two share a similar molecular weight and cyclic scaffold while being catalogued as separate research peptides.
Research Handling and Quality Considerations
Melanotan-2 is typically supplied as a lyophilized (freeze-dried) powder, most commonly in a 10 mg vial. For laboratory work it is reconstituted with bacteriostatic water. As a worked example, adding 2 mL of bacteriostatic water to a 10 mg vial yields a solution at 5 mg/mL; adjusting the diluent volume changes the concentration proportionally. General reconstitution technique is covered in the bacteriostatic water guide and is not repeated here.
Stability and documentation
Reconstituted peptide is generally kept refrigerated, shielded from prolonged light exposure, and handled to minimize repeated freeze-thaw cycles that can degrade peptide integrity. Because purity affects reproducibility, careful researchers review a certificate of analysis (COA) for each lot and vet supplier practices before ordering; guidance on both is available in the supplier vetting overview and the published certificates. Every one of these materials is intended for research use only, not for human consumption.
Frequently Asked Questions
What is the mechanism of Melanotan-2?
Melanotan-2 acts as a non-selective melanocortin receptor agonist. In melanogenesis research its key action is at MC1R, where binding raises cAMP, activates PKA and CREB, and upregulates the MITF transcription factor, which in turn increases tyrosinase expression and melanin synthesis in model cells.
Which melanocortin receptors does Melanotan-2 bind?
Reported data describe activity at MC1R, MC3R, MC4R, and MC5R, with little to no action at MC2R, the adrenal ACTH receptor. This broad coverage is why it is classified as a non-selective agonist rather than a receptor-selective tool.
How does Melanotan-2 differ from alpha-MSH?
alpha-MSH is the natural thirteen-residue melanocortin hormone, while Melanotan-2 is a synthetic cyclic heptapeptide that keeps the His-Phe-Arg-Trp message core but adds a lactam ring and stabilizing substitutions. These changes were engineered to improve metabolic stability and receptor binding relative to the native peptide.
What is the molecular weight of Melanotan-2?
Melanotan-2 has a molecular formula of C50H69N15O9 and an approximate molecular weight of 1024 g/mol, consistent with a cyclic seven-residue peptide. These figures are commonly reported laboratory attributes provided for comparison only.
How is Melanotan-2 related to Melanotan-1 and PT-141?
Melanotan-1 is a linear thirteen-residue alpha-MSH analog, whereas Melanotan-2 is a smaller cyclic analog. PT-141 (bremelanotide) is a deaminated metabolite of Melanotan-2, sharing its cyclic scaffold and a similar molecular weight. All three are studied as distinct melanocortin research peptides.
How is Melanotan-2 stored and handled in the laboratory?
It is usually stored as a lyophilized powder and reconstituted with bacteriostatic water when needed. After reconstitution it is kept cold, shielded from light, and protected from repeated freeze-thaw cycles to preserve peptide integrity for research use only.
References and Further Reading
- Hadley ME, Hruby VJ, and colleagues, University of Arizona: development of melanotropic peptide analogs. PubMed: melanotan II melanocortin analog
- Cone RD: the melanocortin receptor family and its physiology. PubMed: melanocortin receptor Cone
- Abdel-Malek ZA: MC1R signaling in human melanocytes. PubMed: MC1R melanocyte signaling
- MITF as the master regulator of melanogenesis. PubMed: MITF melanogenesis tyrosinase
- Structure-activity studies of alpha-MSH and cyclic analogs. PubMed: alpha-MSH cyclic analog structure activity
- Tyrosinase and the biochemistry of melanin synthesis. PubMed: tyrosinase melanin synthesis melanocyte
- Melanocortin receptor pharmacology and agonist selectivity. PubMed: melanocortin receptor agonist pharmacology
