Melanotan 1 Molecular Weight, Sequence & CAS Reference

Overview of Melanotan 1 (Afamelanotide) Technical Specifications

Melanotan 1, historically designated in literature as [Nle4, D-Phe7]-α-MSH or Afamelanotide, is a synthetic tridecapeptide analog of endogenous alpha-melanocyte-stimulating hormone (α-MSH). Designed to exhibit enhanced metabolic stability relative to the native peptide, Melanotan 1 serves as a foundational reference tool in preclinical investigations focusing on melanocortin receptor activation and downstream physiological signal transduction.

In cell culture and animal models, researchers utilize high-purity Melanotan 1 10mg preparations to characterize binding kinetics, receptor selectivity, and intracellular secondary messenger pathways. Establishing precise physical constants—such as exact molecular weight, sequence fidelity, and counterion content—is essential for accurate molar calculations, serial dilution protocols, and assay reproducibility.

Primary Amino Acid Sequence and Structural Modifications

The primary structure of Melanotan 1 consists of 13 amino acid residues terminated by an N-terminal acetyl group and a C-terminal carboxamide. The complete amino acid sequence is represented using standard single-letter and three-letter notation:

Sequence (Three-Letter Code): Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2 Sequence (Single-Letter Code): Ac-SYS-Nle-EHD-Phe-RGWKPV-NH2

Key structural modifications distinguish Melanotan 1 from native α-MSH. Specifically, the substitution of methionine at position 4 with norleucine (Nle) eliminates susceptibility to oxidative degradation at the thioether side chain. Additionally, replacing L-phenylalanine at position 7 with D-phenylalanine (D-Phe) imparts resistance to enzymatic cleavage by serum endopeptidases. These targeted sequence alterations significantly extend the biological half-life of the peptide in experimental model systems while maintaining high binding affinity for melanocortin receptors.

Chemical Formula, Net Peptide Content, and Molecular Weight

Determining the exact molecular weight and net peptide content is vital when preparing quantitative reagents for comparative binding assays or quantitative liquid chromatography. The primary molecular values established for free-base Melanotan 1 include:

• Chemical Formula: C78H111N21O19 • Monoisotopic Mass: 1645.83 Da • Average Molecular Weight: 1646.85 g/mol • CAS Registry Number: 75921-69-6

It is important for laboratory investigators to distinguish between absolute peptide mass and gross lyophilized weight. Lyophilized peptides exist as salts containing retained counterions and residual moisture. Consequently, gross mass measurement includes both the active peptide cation and the associated counterion species. Accurate molar concentration calculations require multiplying the gross mass by the batch-specific net peptide content (typically reported on the lot-specific Certificate of Analysis).

Impact of Counterion Salt Form: TFA vs. Acetate

Synthetic peptides generated via solid-phase peptide synthesis (SPPS) are routinely cleaved from resins using trifluoroacetic acid (TFA), yielding a peptide trifluoroacetate salt form. Depending on synthesis protocols and downstream purification procedures, Melanotan 1 may be supplied as a TFA salt or converted to an acetate salt form.

The presence of TFA counterions (molecular weight ~114.02 g/mol per salt adduct) or acetate counterions (molecular weight ~60.05 g/mol) directly impacts total molecular weight calculations. Basic residues within Melanotan 1—specifically Arg8, Lys11, and the His6 imidazole nitrogen—can bind multiple counterion molecules depending on pH. When performing cell-based assays or receptor binding studies, researchers must account for TFA or acetate percentage to avoid under-dosing molar concentration in assay buffers.

Preclinical Research Focus: Melanocortin Receptor Binding & Pigmentation Responses

Melanotan 1 acts as a potent non-selective agonist across the melanocortin receptor family, demonstrating high affinity for the melanocortin-1 receptor (MC1R), as well as significant binding at MC3R, MC4R, and MC5R subtypes. In vitro studies demonstrate that MC1R activation by Melanotan 1 stimulates adenylate cyclase activity, driving intracellular cyclic adenosine monophosphate (cAMP) production within melanocytes.

In preclinical animal models, this signal cascade upregulates tyrosinase transcription and activity, promoting eumelanin synthesis. Research protocols investigate these mechanisms to evaluate skin pigmentation responses, photoprotective cellular pathways, and DNA repair kinetics following ultraviolet light exposure. The compound is reserved strictly for non-human in vitro and preclinical laboratory research.

Comparison with Related Melanocortin Receptor Agonists

To understand receptor selectivity and structural activity relationships, laboratory investigators frequently compare Melanotan 1 against other synthetic melanocortin analogs available in our comprehensive catalog of all research peptides.

While Melanotan 1 retains a linear tridecapeptide structure modified directly from α-MSH, cyclic analogs such as Melanotan 2 feature a constrained lactam bridge between Lys10 and Asp5, yielding a truncated heptapeptide (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2) with altered receptor subtype selectivity. Similarly, selective analogs like PT-141 (Bremelanotide) utilize cyclic peptide geometry to alter central nervous system melanocortin pathway activation. Comparing these structural variations provides valuable insight into peptide-receptor docking geometry and signaling cascades across the PX1 research library.

Analytical Characterization: HPLC, MS, and COA Standards

Rigorous physical verification of the melanotan 1 molecular weight sequence is essential prior to bench top utilization. High-Performance Liquid Chromatography (HPLC) coupled with Electrospray Ionization Mass Spectrometry (ESI-MS) serves as the industry standard analytical method for identity confirmation.

Reverse-phase HPLC verifies chromatographic purity, ensuring the absence of deletion sequences or truncated synthesis side-products. Mass spectrometry confirms that the observed m/z ratio corresponds precisely to the calculated monoisotopic molecular weight of 1645.83 Da. Every batch manufactured for PX1 Research undergoes rigorous testing in an ISO 17025 accredited laboratory, producing lot-specific COAs detailing purity percentage, MS mass match, heavy metal testing, and endotoxin assay results.

Reconstitution Guidance and Storage Conditions for Laboratory Benchwork

Lyophilized Melanotan 1 should be stored at -20°C or -80°C in a desiccated environment to prevent premature degradation or hydrolysis. Prior to reconstitution, vials should be allowed to equilibrate to room temperature to minimize condensation formation upon opening.

Reconstitution is typically performed using sterile Bacteriostatic Water (0.9% benzyl alcohol) or sterile endotoxin-free water depending on assay requirements. Non-polar solvents or buffered saline may be required for specific working concentrations. Researchers can utilize our online reconstitution calculator to compute precise volumetric dilutions and stock concentrations for lab use. Aliquoting reconstituted solutions into single-use microcentrifuge tubes minimizes freeze-thaw degradation cycles.

Quality Assurance and Sourcing Protocols at PX1 Research

PX1 Research maintains stringent standard operating procedures for all reference peptides supplied to academic, clinical, and institutional research laboratories. Compounds are synthesized under GMP-compliant facility standards within the USA and undergo full analytical verification prior to distribution.

Every batch of Melanotan 1 is validated by independent third-party testing labs. We verify peptide purity (>98% by HPLC area), confirm chemical structure via tandem mass spectrometry, and verify low endotoxin limits (<0.01 EU/mg) to ensure uncompromised data integrity across all experimental models. Institutional procurement departments interested in high-volume laboratory supply can request custom synthesis parameters and batch reservation through our wholesale lab account department.