α-MSH and its analogues: Melanotan I, Melanotan II, PT-141 and KPV
α-Melanocyte-stimulating hormone (α-MSH) is a 13-residue peptide cut from pro-opiomelanocortin. It acts on the melanocortin receptors MC1R to MC5R. Several research peptides are engineered versions of it, or fragments of it, and their chemistry is easiest to understand side by side.
Sequences
- α-MSH: Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2 (C77H109N21O19S, 1664.9 g/mol).
- Melanotan I (afamelanotide): α-MSH with Nle at position 4 and D-Phe at position 7, linear (C78H111N21O19, 1646.8 g/mol).
- Melanotan II: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, a lactam-bridged cyclic heptapeptide (C50H69N15O9, 1024.2 g/mol).
- PT-141 (bremelanotide): the same cyclic core with a free C-terminal acid instead of an amide (C50H68N14O10, 1025.2 g/mol).
- KPV: Lys-Pro-Val, the C-terminal tripeptide α-MSH(11-13).
Source: PubChem CID 16133793: α-MSH; PubChem CID 16197727: Afamelanotide; PubChem CID 92432: Melanotan II; PubChem CID 9941379: Bremelanotide
Design logic
Replacing methionine 4 with norleucine removes an oxidation site; D-Phe at position 7 increases receptor potency and stability. Cyclising the His-D-Phe-Arg-Trp core through an Asp–Lys lactam bridge, as in Melanotan II, constrains the shape and further resists proteolysis. PT-141 and Melanotan II differ only at the C-terminus (acid vs amide), a difference of about 1 Da that MS can resolve.
Melanotan II was described in 1996 as a 'superpotent cyclic melanotropic peptide'.
KPV in the literature
KPV is studied as the smallest α-MSH fragment with activity in cell models; work in human keratinocytes compared α-MSH, KPV and ACTH signalling, and other groups have studied it in corneal epithelial and intestinal models.
Source: α-MSH, MSH 11-13 KPV and ACTH signalling in human keratinocytes, J Invest Dermatol 2004 (PubMed 15102092); α-MSH(11-13) and corneal epithelial wound models, Exp Eye Res 2006 (PubMed 16965771)
Analytical notes
- Trp and Tyr give strong UV absorbance; these peptides are easy to detect at 280 nm.
- Melanotan II and PT-141 are near-isobaric (≈1 Da apart): check the measured mass carefully.
- Cyclic peptides fragment differently in MS/MS from linear ones.
At Sable
Sable lists these compounds as lyophilised research materials. There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.
Frequently asked questions
What is the difference between Melanotan II and PT-141?
Same cyclic core; Melanotan II has a C-terminal amide, PT-141 a free carboxylic acid.
Is KPV part of α-MSH?
Yes. KPV is residues 11–13 of α-MSH.
Is Melanotan I cyclic?
No. It is linear α-MSH with Nle4 and D-Phe7 substitutions.
Related
- Is PT-141 the same as bremelanotide
- Which catalogue peptides are cyclic, and how are their rings formed
- UK thymosin alpha-1, LL-37, KPV and ARA-290 prices
- Melanocortin peptides hub
- Melanotan II UK prices
- PT-141 UK prices
- KPV UK prices
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- α-MSH 13 aa C77H109N21O19S 1664.9
- Melanotan I [Nle4,D-Phe7]-α-MSH C78H111N21O19 1646.8
- Melanotan II cyclic C50H69N15O9 1024.2
- PT-141 C50H68N14O10 1025.2
- KPV = α-MSH(11-13)
- Sources: PubChem 16133793, 16197727, 92432, 9941379; PubMed 8637402, 15102092, 16965771
- Updated 2026-10-16