Melanotan I

Melanotan 1 is the synthetic linear tridecapeptide [Nle⁴, D-Phe⁷]-alpha-melanocyte-stimulating hormone, also catalogued as afamelanotide and as NDP-alpha-MSH, molecular formula C₇₈H₁₁₁N₂₁O₁₉, molecular weight 1646.9 g/mol, CAS 75921-69-6. It was first described by Sawyer, Hruby, Hadley and co-workers in the Proceedings of the National Academy of Sciences in 1980 as an alpha-melanotropin analogue with unusually prolonged receptor activity. It is supplied here as lyophilised powder for in-vitro laboratory research use only and is not a medicine.

Two substitutions across thirteen residues. Norleucine replaces methionine at position 4, removing the thioether side chain that is the most oxidation-prone group in the native hormone, and L-phenylalanine at position 7 is inverted to D-phenylalanine. The second change is the pharmacologically important one: position 7 lies inside the conserved His-Phe-Arg-Trp message tetrapeptide, and the inverted stereocentre both stabilises the bioactive conformation of that core and eliminates a favoured chymotrypsin-like cleavage site, which is why the 1980 characterisation described the analogue as long acting relative to alpha-MSH.

Not in the strict sense. Curated affinity data describe Melanotan 1 as a full agonist at four of the five human melanocortin receptors, with reported pIC₅₀ 10.0 at MC1R, pKi 8.9 at MC3R, pKi 8.5 to 8.8 at MC4R and pIC₅₀ 9.0 at MC5R, and no activity at MC2R, the adrenocorticotropin receptor. MC1R affinity is roughly an order of magnitude higher than at the other three subtypes, so the accurate description is MC1R-preferring rather than MC1R-selective. Researchers needing genuine subtype discrimination use purpose-built ligands rather than this analogue.

They are distinct chemical entities with different CAS numbers and should never be treated as interchangeable in a protocol. Melanotan 1 is a linear 13-residue analogue of the full alpha-MSH sequence (C₇₈H₁₁₁N₂₁O₁₉, 1646.9 g/mol, CAS 75921-69-6). Melanotan II is a cyclic lactam 7-residue analogue built on the truncated alpha-MSH 4-10 fragment (C₅₀H₆₉N₁₅O₉, 1024.2 g/mol, CAS 121062-08-6), closed by a bridge between the Asp5 side-chain carboxyl and the Lys10 side-chain amine. The consequence is different receptor and stability behaviour: the linear molecule retains a clear order-of-magnitude preference for MC1R, whereas cyclisation flattens activity across MC1R, MC3R, MC4R and MC5R and increases resistance to proteolysis.

Molecular formula C₇₈H₁₁₁N₂₁O₁₉, molecular weight 1646.9 g/mol, CAS number 75921-69-6. The full sequence is Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂, written in analogue notation as [Nle⁴, D-Phe⁷]-alpha-MSH, with a C-terminal primary amide and an N-terminal acetyl group. This vial contains 10mg of lyophilised powder, batch UKPL-326, tested at 99.553% purity by HPLC with the certificate published on this page.

No. Afamelanotide is authorised as a medicine in certain jurisdictions outside the UK, but the material supplied here is not a medicine, holds no marketing authorisation from the MHRA, and is not approved for human or veterinary administration in the UK. It is supplied solely as an analytical reference material for in-vitro laboratory research. Purchasers must be aged 18 or over and must confirm research-only use at checkout. No claim is made or implied regarding any effect in humans.

Because its radioiodinated form, ¹²⁵I-NDP-alpha-MSH, became the standard displacement radioligand for the entire human melanocortin receptor family. A very large proportion of published binding constants for melanocortin ligands, including those for cyclic analogues and for subtype-selective candidates, are expressed as inhibition of ¹²⁵I-NDP-alpha-MSH binding to membranes from cells stably expressing one receptor subtype. The unlabelled peptide is used alongside it as a full-agonist reference point in cAMP accumulation assays.

Because tryptophan at position 9 is photolabile and oxidises readily, producing degradation peaks that are resolvable by RP-HPLC and that reduce the effective concentration of intact peptide in an assay. Tyrosine at position 2 and histidine at position 6 are secondary sites of concern. The norleucine substitution at position 4 has already removed the methionine oxidation site present in native alpha-MSH, so tryptophan is the residue that governs shelf behaviour. Store lyophilised vials at -20°C in the dark, hold reconstituted solution at 2-8°C in amber or foil-wrapped vessels, and reconstitute away from direct sunlight and fluorescent lighting.

Not yet. Batch UKPL-326 is listed at 99.553% purity by HPLC on a supplier-reported certificate of analysis, with identity stated by the supplier, and that certificate is published on this product page. Independent third-party verification of this batch is pending. For an alpha-MSH analogue the impurity worth watching is oxidised tryptophan, which resolves as a distinct RP-HPLC peak, so researchers repeating an assay after extended storage should re-check the chromatogram rather than assume the release figure still holds. Supplied for in-vitro laboratory research only.

You can buy Melanotan 1 in the UK only as an analytical reference material for in-vitro laboratory research. The vial sold here is not a licensed medicine and is not approved for human or veterinary use. Buyers must be 18 or over and confirm research-only use at checkout.

UK Peptide Lab sells Melanotan I 10mg online as a lyophilised powder, dispatched from the UK. The current batch, UKPL-326, has a published certificate of analysis with supplier-reported purity, identity and content figures, and independent third-party verification is pending. Orders placed before 3pm on a working day are dispatched the same day, with free UK delivery over £69.

It is used in vitro as an MC1R-weighted full-agonist reference at the melanocortin receptors. Its radioiodinated form is the standard displacement radioligand for the receptor family. It is also the linear benchmark for cyclic analogues such as the Melanotan II series.

Melanotan 1 prefers MC1R, by roughly an order of magnitude over MC3R, MC4R and MC5R, with no activity at MC2R. Melanotan II loses most of that gradient through cyclisation. Neither is subtype-selective in the strict sense, and both are characterised in transfected cell systems.