Melanotan I (MT1) 10 mg

What is MT1?

The abbreviation MT1 stands for Melanotan I, a linear peptide of 13 amino acids. Its international non-proprietary name (INN) is afamelanotide; in the biochemical literature the compound is also widely known as [Nle4, D-Phe7]-α-MSH or NDP-MSH (NDP-α-MSH). All of these names refer to the same molecule. MT1 is a synthetic analogue of α-melanocyte-stimulating hormone and is classified as an agonist at the melanocortin 1 receptor (MC1R).

Structure: two targeted substitutions

The sequence follows natural α-MSH (Ac-SYSMEHFRWGKPV-NH2) residue by residue – with two exceptions. At position 4, norleucine replaces methionine; at position 7, D-phenylalanine takes the place of L-phenylalanine. Norleucine has an unbranched side chain of the same length as that of methionine but carries no sulfur atom. The D-enantiomer at position 7 alters the spatial orientation within the His-Phe-Arg-Trp motif. In serum stability studies, the modified molecule was described as more resistant to degradation by serum enzymes than the natural sequence.

• Sequence: Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2
• Short form: Ac-SYS[Nle]EH[dF]RWGKPV-NH2
• Molecular formula: C78H111N21O19
• Molar mass: 1646.8 g/mol, based on the free peptide form
• CAS number: 75921-69-6
• PubChem CID: 16197727

MT1 compared with MT2 and KPV

Whereas MT1 retains the full length of α-MSH, MT2 (Melanotan II) reduces the molecule to a core of seven residues and closes it into a ring via a lactam bridge. The two also differ pharmacologically: the literature assigns MT1 to the MC1 receptor, while MT2 addresses several subtypes of the melanocortin receptors. A second relationship concerns the end of the chain. The last three amino acids of MT1, lysine-proline-valine, correspond to residues 11 to 13 of α-MSH and are listed in the catalogue as a tripeptide in their own right under the name KPV. The catalogue groups MT1, MT2 and the copper peptide GHK-Cu together in the Melanocortins & Copper Peptides category.

Research context

Afamelanotide is studied as an MC1R agonist in cell models, above all in melanocyte and melanoma cell lines. Typical readouts in such in-vitro assays are adenylate cyclase activity as a measure of signal transduction at the receptor and tyrosinase activity as a marker of the melanogenesis signalling pathways. MT1 serves here as a defined ligand for work on the signalling cascade of the melanocortin 1 receptor.

Analytics at GPeptides

MT1 is supplied in a 10 mg vial, listed with a purity of ≥ 98 % by HPLC. For identity testing, the mass derived from the molecular formula C78H111N21O19 is decisive: around 1645.84 Da monoisotopic, 1646.8 Da average. For a peptide of this length, the molecule appears in the electrospray spectrum as a series of multiply charged ions, from which the neutral mass is back-calculated. One analytical consequence of norleucine: the +16 Da oxidation variant that is common in methionine-containing peptides cannot form at position 4. MT1 is regularly tested externally by HPLC and mass spectrometry; testing is handled by an independent external laboratory. The available certificates of analysis (COA) can be viewed in the lab area; if a certificate is missing there, it is still pending. The guide Reading a certificate of analysis explains what to look for.