Melanotan 2 Molecular Weight, Sequence & CAS Reference
This technical reference document outlines the physicochemical characteristics, primary sequence, molecular weight, and CAS specifications of Melanotan II (MT-II). Designed exclusively for analytical researchers and laboratory personnel, this guide detail counterion accounting, structural cyclization, and melanocortin receptor binding parameters in vitro.
Quick answer
This technical reference document outlines the physicochemical characteristics, primary sequence, molecular weight, and CAS specifications of Melanotan II (MT-II). Designed exclusively for analytical researchers and laboratory personnel, this guide detail counterion accounting, structural cyclization, and melanocortin receptor binding parameters in vitro.
Key takeaways
- [Melanotan](/research-peptides/melanotan-2) II (MT-II) is a synthetic, cyclic heptapeptide analog of the naturally occurring alpha-melanocyte-stimulating hormone (α-MSH).
- The amino acid sequence of [Melanotan](/research-peptides/melanotan-2) II represents a structural truncation and modification of native α-MSH.
- Accurate gravimetric calculation in quantitative laboratory setups requires exact values for chemical mass and molecular formula.
- Synthetic peptides manufactured via solid-phase peptide synthesis (SPPS) are typically cleaved and purified using acids, resulting in salt-bound peptide preparations.
Introduction to Melanotan II Biochemical Specifications
Melanotan II (MT-II) is a synthetic, cyclic heptapeptide analog of the naturally occurring alpha-melanocyte-stimulating hormone (α-MSH). In preclinical laboratory models, researchers investigate this melanocortin analog primarily for its melanocortin receptor activity and associated skin pigmentation responses. Understanding the fundamental chemical composition—including the precise melanotan 2 molecular weight sequence, empirical formula, and counterion presence—is critical for design of quantitative assays, structural biology experiments, and binding affinity assays.
As a non-selective melanocortin receptor agonist, Melanotan II interacts with multiple melanocortin receptor subtypes, specifically MC1R, MC3R, MC4R, and MC5R. Laboratory researchers utilize high-purity preparations, such as Melanotan II 10mg lyophilized peptide, to establish precise concentration curves in vitro and evaluate receptor-mediated signal transduction without confounding analytical variations.
Primary Structure & Amino Acid Sequence Analysis
The amino acid sequence of Melanotan II represents a structural truncation and modification of native α-MSH. Naturally occurring α-MSH is a 13-amino-acid peptide, whereas Melanotan II is condensed into a cyclic lactam-bridged heptapeptide. This design enhances conformational stability against enzymatic cleavage, particularly by endopeptidases in preclinical assay media.
The published amino acid sequence of Melanotan II is: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2. Structural features of this sequence include an N-terminal acetyl group (Ac) on the Norleucine (Nle) residue, followed by a cyclic core linking the side-chain carboxyl group of L-Aspartic acid (Asp) to the epsilon-amino group of L-Lysine (Lys) via an amide (lactam) bond. Notably, the inclusion of D-Phenylalanine (D-Phe) at position 4 relative to the core core sequence imparts profound structural rigidity and elevated receptor affinity compared to endogenous L-amino acid configurations.
Molecular Weight, Empirical Formula, and CAS Reference
Accurate gravimetric calculation in quantitative laboratory setups requires exact values for chemical mass and molecular formula. The chemical structure of Melanotan II possesses the empirical formula C50H69N15O9.
The monoisotopic mass of free base Melanotan II is calculated at 1023.54 Da, while its chemical average molecular weight is approximately 1024.18 g/mol. In global scientific literature and chemical registry systems, Melanotan II is assigned the CAS Registry Number 121062-08-6. When reviewing analytical documentation, research personnel should cross-reference this CAS number alongside the verified sequence to confirm chemical identity across suppliers.
Salt Form Considerations: Counterions and Net Peptide Content
Synthetic peptides manufactured via solid-phase peptide synthesis (SPPS) are typically cleaved and purified using acids, resulting in salt-bound peptide preparations. Melanotan II is routinely supplied as either a trifluoroacetate (TFA) salt or an acetate salt. The choice of salt form directly alters total vial mass, solubility dynamics, and net peptide content.
Net Peptide Content (NPC) reflects the actual percentage of peptide mass relative to total dry powder weight, which includes residual counterions (TFA or acetate) and bound moisture. For instance, a TFA salt form may yield an NPC ranging between 75% and 85%. If a laboratory protocol requires a 1.0 mM working solution of active compound, calculating solution strength purely from total dry weight without accounting for counterion weight will lead to significant under-dosing in vitro. Investigators should always consult the lot-specific independent Certificate of Analysis to determine the exact net peptide percentage prior to assay preparation.
Structural Mechanics & Melanocortin Receptor Affinity
The core pharmacophore of α-MSH peptides is defined by the tetrapeptide sequence His-Phe-Arg-Trp. In Melanotan II, this motif is contained within the cyclic ring structure provided by the Asp-Lys lactam bridge, stabilized by D-Phe replacement. In vitro binding studies indicate that this forced turn conformation substantially increases binding potency across melanocortin receptor subtypes compared to linear α-MSH sequences.
In cell culture models and tissue preparations, researchers evaluate how Melanotan II activates the MC1R subtype to stimulate cAMP production and downstream tyrosinase activity. These biochemical pathways govern the enzymatic oxidation of L-tyrosine to melanin, providing a primary model for studying melanogenesis and pigmentary cell signaling in vitro.
Comparative Analysis: Melanotan II vs Related Melanocortin Agonists
When designing melanocortin signaling experiments, investigators frequently compare Melanotan II against related synthetic analogs within the class. Key comparisons include Melanotan I (Afamelanotide) and PT-141 (Bremelanotide), both of which share structural homology with endogenous α-MSH.
Melanotan I (Ac-Ser-Tyr-Ser-Met-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2) retains a linear 13-amino-acid sequence with a molecular weight of approximately 1646.85 g/mol, demonstrating high selectivity for MC1R. Conversely, PT-141 is a hydroxylated metabolite derivative of Melanotan II (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH), retaining the cyclic heptapeptide core but possessing a free C-terminal carboxylic acid rather than a C-terminal amide. These subtle structural variations produce distinct sub-type selectivity profiles, receptor internalization rates, and metabolic half-lives in preclinical models. Researchers seeking comprehensive specifications across structural analogs can browse our full catalog of research peptides.
Analytical Characterization: HPLC, Mass Spectrometry, and Quality Control
To ensure precise baseline results in laboratory research, peptide reagents must undergo rigorous physical and analytical verification. High-Performance Liquid Chromatography (HPLC) is employed to assess chemical purity by separating the main target peak from related substances, such as deletion sequences or diastereomers.
Electrospray Ionization Mass Spectrometry (ESI-MS) or MALDI-TOF mass spectrometry is subsequently performed to verify the expected mass profile (m/z [M+H]+ at ~1024.5). Reliable verification requires tandem analysis to rule out residual TFA impurities, endotoxins, or heavy metal contamination. Technical teams should review detailed protocols for HPLC and mass spectrometry protocols to understand analytical threshold criteria.
Storage, Reconstitution, and Solution Stability Parameters
Lyophilized Melanotan II should be stored at -20°C in a desiccated container protected from direct light exposure to maintain long-term stability. Under these conditions, standard solid-state decay is minimized over extended storage intervals.
For laboratory preparation, lyophilized cakes are typically reconstituted using sterile bacteriostatic water or sterile phosphate-buffered saline (PBS, pH 7.4). Researchers can calculate precise solvent volumes and final molar concentrations using our online peptides reconstitution calculator. Reconstituted solutions should be aliquoted into single-use microcentrifuge tubes and stored at -80°C to prevent degradation from repeated freeze-thaw cycles.
Sourcing High-Purity Research Compounds from PX1 Research
PX1 Research provides laboratory-grade peptides manufactured under strict USA production standards within ISO 17025 accredited and GMP-compliant facilities. Every production lot undergoes thorough testing for chemical identity, purity verification via HPLC/MS, and endotoxin assessment to ensure consistency across experimental trials.
Research institutions requiring large-scale allocations or routine batch shipments can explore our specialized bulk lab account program. Additional technical sheets, biochemical structural data, and mechanism guides are accessible via our central peptide research portal.
Frequently Asked Questions
What is the precise molecular weight of Melanotan II?
Melanotan II has an average molecular weight of approximately 1024.18 g/mol and a monoisotopic mass of 1023.54 Da. Always account for counterion weight (e.g., TFA or acetate) when calculating total solid mass for reconstitution.
What is the amino acid sequence and formula for Melanotan II?
The published chemical sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, with an empirical molecular formula of C50H69N15O9.
What is the CAS Registry Number for Melanotan II?
The assigned CAS Registry Number for Melanotan II is 121062-08-6.
How does counterion content (TFA vs Acetate) affect net peptide content?
Counterions bind to basic amino acid residues during peptide synthesis. Depending on the salt form, net peptide content typically ranges between 75% and 85% of total dry powder weight. Gravimetric concentration calculations must adjust for this non-peptide mass using lot-specific COA data.
Why is Melanotan II structured as a cyclic peptide?
Cyclization via a lactam bridge between Asp2 and Lys7 stabilizes the core His-D-Phe-Arg-Trp pharmacophore into a beta-turn conformation, enhancing enzymatic stability and receptor binding affinity compared to linear peptides.
How should reconstituted Melanotan II be handled in laboratory setups?
Once reconstituted with sterile aqueous diluents, solutions should be kept at 2–8°C for short-term assays or aliquoted and stored at -80°C to avoid freeze-thaw degradation during long-term studies.
Is Melanotan II suitable for human or veterinary administration?
No. Melanotan II is supplied strictly as a research chemical for laboratory research use only. It is not intended for human or veterinary use, medical diagnosis, treatment, or clinical application.
How does Melanotan II differ structurally from Melanotan I?
Melanotan I (Afamelanotide) is a linear 13-amino-acid peptide (~1646.85 g/mol) selective for MC1R. Melanotan II is a truncated cyclic heptapeptide (~1024.18 g/mol) that exhibits broader non-selective affinity across MC1R, MC3R, MC4R, and MC5R.
Related pages
All products are sold strictly for laboratory and research use only. Not for human or veterinary use, diagnosis, treatment or consumption. Statements have not been evaluated by the FDA.