Melanotan I Peptide

Melanotan I (afamelanotide, MT-1) is a synthetic analog of alpha-melanocyte-stimulating hormone (α-MSH) with 13 amino acids. Unlike Melanotan II, MT-1 is a linear peptide (not cyclic) and is more selective for the MC1R melanocortin receptor. It has been extensively studied for its role in melanogenesis — the production of melanin pigment in the skin.

Melanotan I binds primarily to MC1R (melanocortin-1 receptor) on melanocytes, activating the cAMP/PKA/CREB signaling cascade. This upregulates MITF (microphthalmia-associated transcription factor), which in turn increases expression of tyrosinase, TRP-1, and TRP-2 — the key enzymes in eumelanin biosynthesis.

The result is increased eumelanin production without requiring UV exposure, a property that has made MT-1 the subject of extensive dermatological and photoprotection research.

Melanotan I research preparations supplied by AminoCore Research are formulated as single-component cyclized peptide solutions or lyophilized powder. The composition is documented below for research traceability and reconstitution planning.

Structural Notes on the Active Component

Afamelanotide is a linear tridecapeptide structural analog of the endogenous alpha-melanocyte stimulating hormone (α-MSH). Two key modifications distinguish it from native α-MSH:

• Nle⁴ substitution: Norleucine replaces methionine at position 4, eliminating oxidation-prone sulfur and conferring resistance to methionine sulfoxide formation during storage
• D-Phe⁷ substitution: The D-isomer of phenylalanine at position 7 confers resistance to proteolytic degradation, dramatically extending biological half-life relative to native α-MSH (which has a plasma half-life of approximately 2 minutes)

Physical Properties

• Physical form: White to off-white lyophilized powder
• Amino acid count: 13 residues
• C-terminal amidation: Yes (-NH₂)
• N-terminal acetylation: Yes (Ac-)
• Solubility: Soluble in bacteriostatic water, sterile water, 0.9% sodium chloride, and acetic acid (1%)
• Purity (HPLC): ≥98%
• Recommended reconstitution diluent: Bacteriostatic water for injection

Unlike multi-ingredient topical cosmetic formulations, this research preparation contains a single defined active peptide species, allowing precise molar calculations for in vitro receptor binding studies, melanocyte culture experiments, and comparative MC1R pharmacology research.

Melanotan I (afamelanotide) is supplied as a sterile lyophilized white powder under inert atmosphere. As a 13-residue linear melanocortin analog containing methionine, tryptophan, and an N-terminal acetyl group, it requires careful handling to preserve secondary structure and minimize oxidative degradation. The following protocol reflects standard laboratory practice for research-grade peptide reconstitution.

Recommended Reconstitution Protocol:

1. Equilibrate to room temperature. Remove the lyophilized vial from -20°C storage and allow it to reach ambient temperature (approximately 20-30 minutes) before opening. This prevents condensation of atmospheric moisture inside the vial.
2. Select reconstitution solvent. Bacteriostatic water for injection (0.9% benzyl alcohol) is the standard diluent for multi-day stability. Sterile water for injection or 0.9% sodium chloride may be used for short-term experiments. For mass-spectrometry validation, dilute acetic acid (0.1%) provides excellent solubility.
3. Calculate target concentration. A typical working concentration is 2 mg/mL. For a 10 mg vial, add 5.0 mL of diluent; for a 5 mg vial, add 2.5 mL. Higher concentrations up to 10 mg/mL are readily achievable due to afamelanotide's good aqueous solubility.
4. Inject solvent slowly. Direct the stream of diluent against the inner wall of the vial — never directly onto the lyophilized cake. This prevents foaming and protects against shear-induced peptide damage.
5. Swirl gently. Rotate the vial in a slow circular motion until the powder is fully dissolved. Do not shake or vortex — agitation can denature the peptide and generate aggregates.
6. Inspect. The reconstituted solution should be clear and colorless. Discard if particulates, cloudiness, or yellow discoloration are observed (the latter can indicate methionine sulfoxide or tryptophan degradation).
7. Aliquot for storage. Transfer single-use volumes to sterile low-binding polypropylene tubes to minimize freeze-thaw cycles.

Compound-specific handling notes:

• Methionine oxidation risk: Met⁴ in the sequence is susceptible to oxidation. Protect from atmospheric oxygen by storing aliquots under nitrogen or argon when possible, and avoid prolonged exposure to peroxide-containing buffers.
• Tryptophan light sensitivity: Trp⁹ can undergo photo-oxidation. Store and handle in amber tubes or shield from direct light, particularly UV sources.
• N-terminal acetylation: The Ac-Ser N-terminus confers resistance to aminopeptidases, but the C-terminal amide and overall linear backbone still permit chymotryptic cleavage in biological matrices — use protease inhibitors in cell culture supernatant assays.
• Aseptic technique: Always work in a laminar flow hood or with sterile filtered diluents to prevent microbial contamination, especially when using non-bacteriostatic water.

This material is sold strictly for in vitro and preclinical laboratory research. It is not for human or veterinary use, food, or cosmetic application.

Proper storage of Melanotan I (afamelanotide) is essential for maintaining peptide integrity and ensuring reproducible research outcomes. The Nle⁴ and D-Phe⁷ substitutions provide enhanced stability relative to native α-MSH, but standard peptide handling precautions still apply.

Lyophilized Powder Storage

• Long-term storage: Store at -20°C or colder in a frost-free freezer. Under these conditions, the lyophilized peptide remains stable for 24+ months with negligible degradation
• Short-term storage: 2-8°C (standard refrigeration) is acceptable for up to 30 days when active use is anticipated
• Transit / ambient exposure: The lyophilized form tolerates room temperature (15-25°C) for shipping periods up to 14 days without significant loss of activity, owing to the absence of free water
• Container integrity: Keep vial sealed under inert atmosphere until reconstitution. Avoid repeated temperature cycling

Reconstituted Solution Storage

• Refrigerated (2-8°C): Stable for approximately 28 days when reconstituted with bacteriostatic water containing 0.9% benzyl alcohol
• Sterile water reconstitution: Use within 7 days when stored at 2-8°C due to absence of preservative
• Frozen aliquots (-20°C): Single-use aliquots remain stable 3+ months; avoid freeze-thaw cycles which can promote aggregation
• Room temperature: Not recommended; limit to 24 hours maximum during active experimental use

Compound-Specific Stability Notes

Afamelanotide demonstrates superior chemical stability compared to native α-MSH due to the norleucine-for-methionine substitution at position 4, which eliminates the methionine oxidation pathway that destabilizes the parent hormone. The tryptophan residue at position 9, however, remains susceptible to photo-oxidation. Practical implications:

• Light protection: Store in amber vials or in original light-blocking packaging; minimize fluorescent and UV exposure during handling
• Oxygen exposure: Limit headspace and avoid prolonged exposure to ambient atmosphere in reconstituted form
• pH considerations: Solution stability is optimal at slightly acidic to neutral pH (5.5-7.0); avoid strongly alkaline diluents
• Aggregation monitoring: Inspect solutions visually before use; discard if precipitation, cloudiness, or color change is observed

For research applications requiring long-term reproducibility, preparing single-use frozen aliquots immediately after reconstitution is recommended over repeated withdrawal from a single stock vial.