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Molecular Weight
Purity
Storage
Appearance
Solubility
01
Melanotan I (MT-I), also known by its international non-proprietary name afamelanotide, is a synthetic 13-residue analogue of α-melanocyte-stimulating hormone (α-MSH). It keeps the full α-MSH length and both capped termini, with two changes: norleucine in place of methionine at position 4, and D-phenylalanine in place of L-phenylalanine at position 7. These give it greater stability and potency than the native hormone.
It is a linear peptide, unlike the cyclic analogues Melanotan II and PT-141 (bremelanotide), which makes it a useful comparator for studying how ring formation changes melanocortin receptor behaviour. Afamelanotide is the active ingredient of a medicine approved in some countries; the material listed here is supplied solely as a lyophilized reference compound for in vitro research.
02
Melanotan I follows the native α-MSH sequence with targeted changes.
Sequence
Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂, with an acetylated N-terminus and amidated C-terminus, as in native α-MSH.
Nle4
Norleucine replaces methionine. It has the same side-chain length but no sulfur, removing the main oxidation risk of α-MSH.
D-Phe7
Inverting the stereochemistry at position 7, within the His-Phe-Arg-Trp core that all melanocortins share, increases potency and resistance to enzymatic cleavage.
Aromatic residues
Tyr2, D-Phe7 and Trp9 give strong UV absorbance at 280 nm and natural fluorescence. Trp9 is the main light-sensitive residue.
C-terminal Lys-Pro-Val
The last three residues are the same Lys-Pro-Val sequence available separately in this catalogue as the tripeptide KPV.
Charge
Arg8 and Lys11 (and partly His6) are positive and Glu5 negative; with both termini capped, the net charge is about +1 to +2 at neutral pH.
03
Research on Melanotan I centres on the melanocortin receptors.
Melanocortin receptors
MC1R to MC5R are G protein-coupled receptors that signal mainly through cAMP. Melanotan I is a potent agonist at several of them, particularly MC1R, which is expressed on melanocytes.
Binding and signalling assays
Competition binding with labelled α-MSH analogues and cAMP assays in cells expressing individual receptors are used to profile its potency across MC1R, MC3R, MC4R and MC5R.
Linear versus cyclic
Comparing it with cyclic analogues such as Melanotan II shows how restricting the backbone affects receptor selectivity, potency and stability.
Conformation
NMR and circular dichroism studies describe a flexible peptide that samples several conformations around the His-Phe-Arg-Trp core.
These findings are cited as research context only; no effects are claimed for this material.
04
Melanocortin receptor panels
A reference agonist for normalising binding and cAMP data across MC receptor subtypes.
Linear versus cyclic comparisons
Paired with Melanotan II and PT-141 to study the effects of cyclisation.
Oxidation control
With norleucine in place of methionine, it serves as an oxidation-resistant counterpart to methionine-containing α-MSH in stress studies.
Aromatic peptide chromatography
Its three aromatic residues make it a good test compound for UV and fluorescence detection and for column selectivity.
05
Storage
Store the lyophilized powder at −20 °C, sealed, desiccated and protected from light.
Light sensitivity
Trp9 can photo-oxidise to kynurenine (+4 Da) and N-formylkynurenine (+32 Da). Use amber or opaque containers and handle under subdued light.
No methionine oxidation
Because Nle4 replaces methionine, the +16 Da methionine sulfoxide seen with α-MSH does not occur.
Reconstitution
Soluble in water and dilute acetic acid. A slightly acidic solution is a good default for stock preparation.
Solutions
Aliquot into single-use volumes in low-binding polypropylene tubes and freeze; avoid repeated freeze–thaw cycles.
06
Melanotan I is straightforward to detect, with attention to stereochemistry and tryptophan oxidation.
HPLC
Reversed-phase C18 with a 0.1% TFA gradient gives one main peak. Detect at 214 nm, or at 280 nm for its aromatic residues.
Mass spectrometry
ESI gives [M+2H]²⁺ and [M+3H]³⁺ ions at about m/z 823.9 and 549.6 (monoisotopic; about 824.4 and 549.9 by average mass).
Confirming Nle4
Norleucine (113.08 Da) is lighter than methionine (131.04 Da) by 18 Da, so MS readily confirms that Met is absent. Nle has the same mass as Leu and Ile, so distinguishing it from those requires amino acid analysis or chromatography against standards.
Confirming D-Phe7
MS cannot distinguish D- from L-Phe. Chiral amino acid analysis after hydrolysis, or comparison with the L-Phe7 epimer by HPLC, confirms the configuration.
Impurity profile
Typical checks include the L-Phe7 epimer, tryptophan oxidation products, deletion sequences and the non-acetylated or free-acid forms.
07
It has the same 13-residue length and capped ends, but norleucine replaces methionine at position 4 and D-phenylalanine replaces L-phenylalanine at position 7. These changes improve stability and potency.
Melanotan I is linear and full-length (13 residues, about 1647 g/mol). Melanotan II is a shorter cyclic peptide (about 1024 g/mol) whose ring is formed by a lactam bridge between aspartate and lysine side chains.
Norleucine has the same chain length as methionine but no sulfur atom, so it cannot oxidise to the sulfoxide. This removes the main oxidation risk of native α-MSH.
Trp9 can oxidise under light to kynurenine (+4 Da) and N-formylkynurenine (+32 Da). Store and handle it protected from light.
By chiral amino acid analysis after hydrolysis, for example with Marfey’s reagent or a chiral column, or by HPLC comparison with the L-Phe7 epimer. Mass spectrometry cannot tell D- and L-forms apart.
No. Although afamelanotide is used in an approved medicine in some countries, the material listed here is supplied strictly as a reference compound for laboratory and analytical research and is not for human or animal use.
Melanotan I Research Reference. (2026). Pure Peptides Labs Research Catalogue. Retrieved from https://purepeptideslabs.net/research-catalogue/melanocortin-research-peptides/melanotan-i/
Materials listed on this platform are supported by independent testing and published documentation for laboratory research contexts.
