Melanotan I, also known as afamelanotide, is a synthetic tridecapeptide analogue of alpha-melanocyte-stimulating hormone: Ac-Ser-Tyr-Ser-Nle-Glu-His-DPhe-Arg-Trp-Gly-Lys-Pro-Val-NH2. Molecular formula C78H111N21O19, molecular weight 1646.8 g/mol.
It is a close analogue of native alpha-MSH, differing at two positions. Methionine at position four is replaced with norleucine, removing an oxidation-prone residue, and the phenylalanine at position seven is the D-isomer, which resists peptidase cleavage. Both substitutions extend the working half-life without altering the linear thirteen-residue architecture of the parent hormone.
Research context
Melanotan I is studied as a melanocortin receptor agonist with activity weighted toward MC1R, the receptor expressed on melanocytes. Published work examines melanogenesis — tyrosinase activity, eumelanin synthesis and the cellular response to ultraviolet exposure in cultured melanocyte preparations.
The comparison with Melanotan II is the useful frame. MT-I retains the linear structure of native alpha-MSH and its more MC1R-selective profile; MT-II is a shortened cyclic analogue with broader melanocortin activity, including at MC4R. For work where pigmentation pathways are the endpoint rather than a confound, the narrower selectivity of MT-I is the reason to choose it.
For a fuller treatment of the sequence, published models and technical data, see the Melanotan I research guide.
Specification
CAS number 75921-69-6. Supplied as a white lyophilized powder, soluble in water. This batch assayed at 99.74% purity, verified by HPLC and LC-MS at ILS Lab.
Handling
Reconstitute with bacteriostatic or sterile water, introducing the diluent against the vial wall and swirling gently rather than shaking. Store lyophilized at −20°C protected from light; refrigerate at 2–8°C once reconstituted.
Ships with a batch-specific Certificate of Analysis. Cross-check the batch ID printed on your vial against the CoA before use — see the guide to reading a CoA if you are unfamiliar with the format.
Frequently asked questions about Melanotan I
Melanotan I or Melanotan II for melanogenesis research?
Melanotan I, in most cases. MT-I is weighted toward MC1R — the receptor expressed on melanocytes and the one that drives pigmentation. MT-II is active across MC1R, MC3R, MC4R and MC5R, so any observation carries contributions from central receptors as well. Where pigmentation pathways are the endpoint rather than a side effect, the narrower profile makes attribution cleaner.
Why is Melanotan I also called afamelanotide?
Same molecule, two naming conventions. Afamelanotide is the international nonproprietary name; Melanotan I is the research designation that predates it. Suppliers and literature use both, which occasionally causes confusion when searching — a search on one term will miss papers using the other.
What do the two modifications do?
Norleucine at position four replaces methionine, removing the most oxidation-prone residue in the native sequence — methionine oxidises readily on air exposure, adding 16 Da and altering the molecule. D-phenylalanine at position seven resists peptidase cleavage. Together they extend working half-life substantially while leaving the linear thirteen-residue architecture intact, which is why MT-I still behaves like native alpha-MSH where MT-II does not.
How stable is Melanotan I in solution?
Better than native alpha-MSH, largely because of the norleucine substitution. Reconstitute with bacteriostatic or sterile water, introducing the diluent against the vial wall and swirling gently. Store lyophilized at −20°C protected from light; refrigerate at 2–8°C once reconstituted and avoid repeated freeze-thaw cycles.
Research use only. Not for human or veterinary use, not for use in diagnostic procedures, and not evaluated by the U.S. Food and Drug Administration.
