What Is the Structure of Melanotan 1 Peptide?

By the BehemothLabz Research Content Team | Last Updated: July 2026

Disclaimer: Melanotan 1 is a research compound not approved by the U.S. Food and Drug Administration (FDA) for human or veterinary use. It is not intended to diagnose, treat, cure, or prevent any disease. This content is for informational purposes only. Always consult a licensed medical professional before making any health-related decisions.

Note on Regulatory Status: Afamelanotide, the same amino acid sequence as Melanotan 1 received FDA approval in October 2019 as Scenesse® for the prevention of phototoxicity in adults with erythropoietic protoporphyria (EPP). The FDA-approved form is a 16 mg subcutaneous implant manufactured under GMP conditions. The research-grade material described in this article is not the same product as Scenesse® and is not manufactured or intended for clinical use. Researchers should keep this regulatory distinction in mind when sourcing MT1 for preclinical study design.

Quick Answer: Melanotan 1 is a linear, 13-amino acid peptide built from the natural hormone alpha-MSH. Two substitutions, norleucine at position 4 and D-phenylalanine at position 7, distinguish it structurally and give it a more MC1R-selective binding profile than the cyclic Melanotan 2. Research on its downstream effects is still evolving and remains largely preclinical.

Why Peptide Structure Is Getting a Second Look

Peptide chemistry has quietly become one of the more fascinating corners of research science, and Melanotan 1 (MT1) sits right in the middle of that conversation. It isnt a new molecule; researchers have studied it since the 1980s, but renewed interest in melanocortin receptor biology has pulled it back into focus. What makes MT1 worth understanding isnt hype; its the elegance of its design. A handful of small structural tweaks to a naturally occurring hormone changed how the molecule behaves in laboratory models entirely. Thats the kind of detail that tends to catch the attention of anyone exploring peptide science, whether theyre new to the topic or have spent years around it.

What Is Melanotan 1, Structurally Speaking?

Melanotan 1 is a synthetic linear peptide modeled directly on alpha-melanocyte-stimulating hormone (α-MSH), a naturally occurring 13-amino acid hormone involved in melanocortin receptor signaling. MT1 keeps the same 13-residue backbone as α-MSH but introduces two deliberate substitutions that researchers use to study receptor selectivity and peptide stability in laboratory settings.

The Native α-MSH Backbone

Natural α-MSH follows this sequence:

Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂. Every peptide in the melanocortin family is built on some variation of this scaffold, which is why understanding it first makes MT1s modifications easier to visualize. Think of it as the parent template that peptide chemists modify one residue at a time.

The Two Key Substitutions in MT1

• Norleucine at position 4 replaces the native methionine. Methionine is prone to oxidation, which can degrade a peptides structural integrity over time in solution. Norleucine is structurally similar but resistant to that oxidative breakdown, which researchers associate with improved stability during storage and handling.
• D-phenylalanine at position 7 replaces the native L-phenylalanine. This single change in molecular orientation is significant because enzymes in biological systems are typically built to recognize L-amino acids, so swapping in the D-isomer sterically obstructs enzymatic cleavage at that peptide bond, extending the peptides resistance to degradation in laboratory models.

Together, these substitutions are commonly written in shorthand as [Nle⁴, D-Phe⁷]-α-MSH, a naming convention researchers use to describe exactly where MT1 diverges from the native hormone. This same sequence is also known by its pharmaceutical name, afamelanotide (CAS 75921-69-6).

How Does MT1s Structure Compare to Melanotan 2 and PT-141?

This is one of the most common points of confusion in peptide research circles, so its worth addressing directly.

Linear vs. Cyclic Architecture

MT1 is a linear tridecapeptide; its 13 amino acids form a straight chain with no bonds looping back on themselves. Melanotan 2 (MT2), by contrast, is a cyclic heptapeptide. MT2s structure includes a lactam bridge formed between the side chains of an aspartic acid and a lysine residue, effectively locking the peptide into a ring shape.

Shared Core Sequence

Despite their different overall shapes, MT1 and MT2 share a four-residue core: His-D-Phe-Arg-Trp. This shared segment is considered the primary pharmacophore — the structural region responsible for interacting with melanocortin receptors. This same tetrapeptide core also appears in PT-141 (bremelanotide), a cyclic peptide derived from MT2s structure that is studied for its MC4R-driven effects rather than MC1R-driven pigmentation. The shared core across all three peptides explains why they engage melanocortin receptors despite differing overall architectures, while the surrounding structure is what determines which receptor subtype each one favors.

Why the Difference Matters for Research Design

Because MT1 retains a linear structure closer to native α-MSH, its generally regarded in the literature as a selective MC1R agonist, with comparatively minimal activity at MC3R, MC4R, and MC5R. MT2s cyclic, more compact structure, by contrast, is a non-selective agonist that engages MC1R, MC3R, MC4R, and MC5R with broadly comparable affinity which is why MT2 research has historically reported effects beyond pigmentation, including appetite and cardiovascular signaling. Researchers choosing between the two often base their decision on which receptor pathway theyre isolating for study.

How MT1s Structure Drives Downstream Signaling

Structure only matters because of what it does once it reaches a receptor. When MT1 engages MC1R, the receptor activates adenylyl cyclase, triggering intracellular cyclic AMP (cAMP) elevation. Elevated cAMP activates protein kinase A (PKA), which phosphorylates the microphthalmia-associated transcription factor (MITF), the master regulator of melanogenesis gene expression, including the tyrosinase enzyme responsible for melanin synthesis.

The D-Phe⁷ substitutions resistance to enzymatic cleavage means the receptor interaction is sustained longer than it would be with native α-MSH, which researchers associate with a more prolonged PKA/MITF activation window in experimental models. This signaling chain, MC1R → adenylyl cyclase → cAMP → PKA → MITF → melanogenesis, is the primary pathway examined in MT1 preclinical research, and its the mechanistic link between the peptides structure and the melanogenic effects observed in laboratory studies.

How Molecular Weight and Formula Reflect the Structure

MT1s structural modifications translate into specific, measurable physical properties that researchers rely on for identification and quality verification:

• Molecular formula: C₇₈H₁₁₁N₂₁O₁₉
• Molecular weight: Approximately 1,646.87 g/mol
• CAS Number: 75921-69-6 (afamelanotide / NDP-α-MSH)
• PubChem CID: 16197727
• Synonyms: Afamelanotide, NDP-α-MSH, MT-1, CUV1647, [Nle⁴, D-Phe⁷]-α-MSH
• Mass spectrometry signature: The intact peptide is typically identified via its doubly charged precursor ion, a detail used in analytical and forensic peptide research to confirm identity and purity.
• Termini modifications: The N-terminal acetylation and C-terminal amidation both contribute to the peptides overall stability profile, protecting the ends of the chain from exopeptidase activity in solution.

These arent cosmetic details for anyone running comparative studies; small variances in molecular weight or termini can indicate degradation, incomplete synthesis, or batch inconsistency, which is why third-party verification matters (more on that below).

What Are the Risks and Limitations of Melanotan 1 Research?

This section is important reading for anyone following research on Melanotan 1.

1. Handling Precautions: Melanotan 1 should be handled by trained laboratory personnel only, in a controlled environment. Use appropriate PPE. Avoid direct skin contact or inhalation.
2. Exposure Risks: MT1 is a research peptide thought to interact with melanocortin receptor pathways in preclinical models. No human safety profile has been established for research-grade material.
3. Storage: Store lyophilized Melanotan 1 at −20°C in a dry, dark environment. Protect from light, heat, and moisture to preserve structural integrity.
4. Toxicity and Data Limitations: No chronic toxicity data exist for research-grade Melanotan 1. All findings are drawn from short-duration preclinical models only.
5. Structural Degradation Risk: Improper storage or repeated freeze-thaw cycles can compromise the peptides structural conformation, potentially skewing experimental results.
6. Batch Variability: Without third-party testing, researchers cannot confirm that a given batch matches the intended amino acid sequence or purity level.
7. Analytical Complexity: Confirming structural identity requires mass spectrometry or HPLC equipment and expertise not available in every research setting.

Where Do Researchers Source Melanotan 1?

For lab-grade Melanotan 1, researchers typically look for independently third-party tested batches with a Certificate of Analysis (COA) available per lot, confirming both purity and structural accuracy. Those working specifically with the linear MT1 analogue for structural or receptor-selectivity comparison work can find research-grade Melanotan 1 Nasal Spray at BehemothLabz, formulated for controlled laboratory studies and backed by BehemothLabzs quality control and testing protocols, which detail the third-party verification process researchers rely on to confirm sequence accuracy and purity before use in study design.

Conclusion

Melanotan 1s structure is what makes it a durable subject of interest in melanocortin research: a familiar 13-amino acid hormone backbone, refined with two targeted substitutions that improve stability and sharpen its selectivity for MC1R. Research into how that structure translates to downstream signaling remains early-stage in the research-grade context, and long-term data are still evolving. For researchers tracking this space, BehemothLabz offers COA-verified Melanotan 1 for laboratory use.

Frequently Asked Questions

How many amino acids are in Melanotan 1?

Melanotan 1 contains 13 amino acids, matching the length of natural alpha-MSH, arranged in a linear (non-cyclic) chain, making it a tridecapeptide, not a tetradecapeptide.

What makes Melanotan 1s structure different from alpha-MSH?

Two substitutions: norleucine replaces methionine at position 4, and D-phenylalanine replaces L-phenylalanine at position 7.

Is Melanotan 1 the same structure as Melanotan 2?

No. MT1 is linear with 13 amino acids; MT2 is cyclic with 7 amino acids. They share only a four-residue core sequence, and that shared core is also found in PT-141 (bremelanotide).

Why does the D-phenylalanine substitution matter?

D-phenylalanine (D-Phe) at position 7 is the mirror image of the natural L-phenylalanine. Because biological proteases are stereospecific for L-amino acids, the D-Phe substitution sterically obstructs enzymatic cleavage at that peptide bond, extending the peptides resistance to degradation in solution. Combined with the Nle⁴ oxidation resistance, these two modifications extend the peptides functional stability in experimental timelines compared to native α-MSH.

What is Afamelanotide, and is it the same as Melanotan 1?

Yes. Afamelanotide is the International Nonproprietary Name (INN) for the same compound: [Nle⁴, D-Phe⁷]-α-MSH, CAS 75921-69-6. Afamelanotide was approved by the FDA in 2019 as Scenesse® for erythropoietic protoporphyria. Research-grade Melanotan 1 shares the same amino acid sequence but is not a pharmaceutical product and is not manufactured or intended for human use.

What receptors does Melanotan 1 bind to?

MT1 is considered a selective agonist of MC1R, with comparatively minimal activity at MC3R, MC4R, and MC5R. That selectivity is what distinguishes it from the non-selective Melanotan 2, which engages all four receptor subtypes with broadly comparable affinity — a difference that matters for researchers trying to isolate pigmentation-specific signaling from broader melanocortin effects.

What is the CAS number for Melanotan 1?

CAS 75921-69-6. Also listed under the synonyms Afamelanotide, NDP-α-MSH, [Nle⁴, D-Phe⁷]-α-MSH, and MT-1.

What is the pharmacophore of Melanotan 1?

The minimal pharmacophore, the structural region essential for melanocortin receptor binding, is the four-residue core sequence His-D-Phe-Arg-Trp (positions 6–9 in the full 13-residue chain). This tetrapeptide core is shared between MT1, MT2, and PT-141/bremelanotide, which is why all three peptides engage melanocortin receptors despite differing overall architectures.

Where can researchers find structurally verified Melanotan 1?

Researchers typically source COA-verified batches from suppliers offering third-party testing, such as BehemothLabzs Melanotan 1 Nasal Spray, to confirm sequence accuracy and purity before use in study design.

References

1. Sawyer, T. K., Sanfilippo, P. J., Hruby, V. J., et al. (1980). 4-Norleucine, 7-D-phenylalanine-alpha-melanocyte-stimulating hormone: a highly potent alpha-melanotropin with ultralong biological activity. Proceedings of the National Academy of Sciences, 77(10), 5754–5758. https://pmc.ncbi.nlm.nih.gov/articles/PMC350149/
2. Dorr, R. T., Ertl, G., Levine, N., et al. (2013). A review and update on melanocyte-stimulating hormone therapy: afamelanotide. Journal of Drugs in Dermatology, 12(7), 775–779. https://pubmed.ncbi.nlm.nih.gov/23884489/
3. Minder, E. I., Barman-Aksoezen, J., & Schneider-Yin, X. (2017). Pharmacokinetics and Pharmacodynamics of Afamelanotide and Its Clinical Use in Treating Dermatologic Disorders. Clinical Pharmacokinetics, 56(8), 815–823. https://pubmed.ncbi.nlm.nih.gov/28063031/
4. Hadley, M. E., Abdel Malek, Z. A., Marwan, M. M., Kreutzfeld, K. L., & Hruby, V. J. (1985). [Nle4, D-Phe7]-alpha-MSH: a superpotent melanotropin that irreversibly activates melanoma tyrosinase. Endocrine Research, 11(3-4), 157–170. https://pubmed.ncbi.nlm.nih.gov/3009169/
5. Dorr, R. T., Dvorakova, K., Brooks, C., Lines, R., Levine, N., Schram, K., Miketova, P., Hruby, V., & Alberts, D. S. (2000). Increased eumelanin expression and tanning is induced by a superpotent melanotropin [Nle4-D-Phe7]-alpha-MSH in humans. Photochemistry and Photobiology, 72(4), 526–532. https://bioone.org/journals/photochemistry-and-photobiology/volume-72/issue-4/0031-8655_2000_072_0526_IEEATI_2.0.CO_2/Increased-Eumelanin-Expression-and-Tanning-is-Induced-by-a-Superpotent/10.1562/0031-8655(2000)072%3C0526:IEEATI%3E2.0.CO;2.short

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