Melanotan II (MT-II) is a synthetic cyclic heptapeptide studied as a non-selective agonist of the melanocortin receptor family, with activity spanning MC1R, MC3R, MC4R, and MC5R. It is a lactam-bridged analog of alpha-melanocyte-stimulating hormone (alpha-MSH) and is used in laboratory research as a stable, superpotent probe of melanocortin signaling and the melanogenesis pathway. This article summarizes its structure, mechanism, and the peer-reviewed research record, along with standard handling considerations. It is intended strictly for in-vitro and laboratory research context and is not guidance for human or animal use.
What Is Melanotan II?
Melanotan II is a cyclic seven-residue peptide with the sequence Ac-Nle4-Asp5-His6-D-Phe7-Arg8-Trp9-Lys10-NH2, in which a lactam bridge between the Asp5 and Lys10 side chains constrains the molecule into a rigid conformation (Dorr 1996). It was developed at the University of Arizona from systematic medicinal-chemistry work aimed at producing metabolically stable, high-potency analogs of alpha-MSH. The endogenous hormone alpha-MSH is a linear 13-residue peptide that is rapidly degraded; cyclization and the D-Phe7 and Nle4 substitutions in MT-II improve resistance to enzymatic breakdown and lock in the active beta-turn geometry, which is why it is described in the literature as a "superpotent" melanotropic peptide (Dorr 1996).
Because it engages multiple melanocortin receptor subtypes rather than a single one, MT-II is used as a broad tool compound for studying melanocortin pharmacology in cell-based and animal models, in contrast to more receptor-selective analogs.
Mechanism of Action
The melanocortin system comprises five G-protein-coupled receptors (MC1R through MC5R) and endogenous ligands derived from proopiomelanocortin (POMC). MT-II binds and activates these receptors as an agonist. The receptor most associated with pigmentation research is MC1R, which is expressed on melanocytes.
When a melanocortin agonist binds MC1R, the receptor couples to the Gs protein and activates adenylate cyclase, raising intracellular cyclic AMP (cAMP). Elevated cAMP activates protein kinase A (PKA), which phosphorylates the transcription factor CREB and upregulates microphthalmia-associated transcription factor (MITF). MITF in turn drives expression of tyrosinase and other enzymes that catalyze the conversion of tyrosine into eumelanin. This cAMP-MITF-tyrosinase cascade is the core in-vitro mechanism by which melanocortin agonists increase melanin synthesis in cultured melanocytes.
Structural Basis of Receptor Activation
Structural biology has clarified how melanocortins engage MC1R. Cryo-electron microscopy of the human MC1R-Gs complex bound to alpha-MSH, the analog afamelanotide, and the synthetic agonist SHU9119 resolved the receptor at near-atomic resolution (3.0, 2.7, and 3.1 angstrom, respectively) and mapped the orthosteric pocket that recognizes the conserved His-Phe-Arg-Trp (HFRW) motif shared by melanocortin ligands. The structures also revealed a critical role for a calcium ion in coordinating ligand binding (Ma 2021). Because MT-II presents the same HFRW pharmacophore in a conformationally constrained scaffold, these structures provide a framework for understanding how cyclic analogs stabilize the active receptor state.
Published Research Overview
The research record on Melanotan II spans peptide design, receptor pharmacology, structural biology, and early human pharmacology conducted during its development. A pilot phase-I study characterized MT-II as a superpotent cyclic melanotropic peptide and reported measurable increases in cutaneous pigmentation as assessed by quantitative reflectance, alongside dose-related effects such as nausea and fatigue (Dorr 1996). This report is cited here as the historical scientific record documenting the compound's pharmacology; it does not constitute a use recommendation, and the material supplied by Dynamite Research Peptides is for laboratory research only.
Work on the closely related analog NDP-MSH (also written [Nle4, D-Phe7]-alpha-MSH) illustrates how melanocortin agonists interact with MC1R genetics. In a controlled study of 77 individuals, NDP-MSH produced a statistically significant increase in melanin density versus placebo (p < 0.001), and the effect was larger in carriers of common MC1R variant alleles (such as Arg151Cys and Arg160Trp) than in those with no variants (Fitzgerald 2006). This work is relevant context for MT-II research because both compounds act through the same MC1R melanogenesis pathway, though the two peptides are distinct molecules.
More broadly, the melanocortin-1 receptor remains an active subject of pharmacological and structural review. A 2025 review in the Journal of the European Academy of Dermatology and Venereology surveyed the biology of chronic MC1R activation and the melanocortin pathway, reflecting continued scientific interest in this receptor system as of 2025 (Bohm 2025). Reviews of this kind place tool compounds such as MT-II within the wider context of melanocortin receptor research.
How Melanotan II Differs From PT-141 and NDP-MSH
Melanotan II, PT-141 (bremelanotide), and NDP-MSH (afamelanotide) are all melanocortin agonists derived from alpha-MSH research, but they differ in receptor emphasis. MT-II is broadly non-selective across MC1R, MC3R, MC4R, and MC5R, which makes it a general melanocortin probe. PT-141 is an active metabolite of MT-II whose profile is shifted toward the central MC3R/MC4R axis rather than the MC1R-linked pigmentation pathway. NDP-MSH is a linear (non-cyclic) analog that also acts strongly at MC1R. These distinctions determine which compound researchers select for a given melanocortin study.
Frequently Asked Questions
What receptors does Melanotan II target?
MT-II acts as a non-selective agonist across the melanocortin receptor family, including MC1R, MC3R, MC4R, and MC5R (Dorr 1996). MC1R is the subtype most associated with the melanogenesis pathway studied in melanocyte cell culture.
How does Melanotan II relate to alpha-MSH?
MT-II is a cyclic, lactam-bridged analog of the endogenous hormone alpha-MSH. Cyclization and the Nle4 and D-Phe7 substitutions improve enzymatic stability and lock in the active conformation, giving it greater potency and duration than the native peptide (Dorr 1996).
Is Melanotan II the same as PT-141?
No. PT-141 (bremelanotide) is an active metabolite and analog of MT-II, but it is a distinct heptapeptide with a pharmacological profile weighted toward central MC3R/MC4R signaling rather than the MC1R pigmentation pathway.
What purity does Dynamite Research Peptides provide?
Our Melanotan II is 99%+ purity with a Certificate of Analysis available for every batch.
Storage & Handling
Melanotan II is supplied as a lyophilized (freeze-dried) powder. Store it at -20 degrees C or below, protected from light and moisture. Reconstitute only with an appropriate sterile solvent immediately before laboratory use, keep reconstituted material refrigerated, and avoid repeated freeze-thaw cycles, which can degrade peptide integrity. As a general handling note, melanocortin peptides in solution are best protected from prolonged light exposure.
Research Note (Updated July 2026)
As of 2026, the melanocortin system remains an active area of structural and cell-biology research, with cryo-EM MC1R structures (2021) and recent pharmacological reviews (through 2025) continuing to inform how researchers use melanocortin agonists such as Melanotan II as tool compounds (Ma 2021; Bohm 2025). This article reflects the peer-reviewed record available at the time of update.
All products are for research use only — not for human or animal consumption. Nothing here is medical advice or a therapeutic, dosing, cosmetic, or human-use recommendation.