---
title: "α-MSH and its analogues: Melanotan I, Melanotan II, PT-141 and KPV | Sable Peptides"
description: "How Melanotan I (afamelanotide), Melanotan II, PT-141 (bremelanotide) and the KPV tripeptide relate to α-melanocyte-stimulating hormone: sequences, cyclisation, PubChem data and research background. Research use only."
canonical: https://www.sablepeptides.co.uk/guides/melanocortin-peptides-alpha-msh-analogues
dateModified: 2026-10-16
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

# 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](https://pubchem.ncbi.nlm.nih.gov/compound/16133793); [PubChem CID 16197727: Afamelanotide](https://pubchem.ncbi.nlm.nih.gov/compound/16197727); [PubChem CID 92432: Melanotan II](https://pubchem.ncbi.nlm.nih.gov/compound/92432); [PubChem CID 9941379: Bremelanotide](https://pubchem.ncbi.nlm.nih.gov/compound/9941379)

## 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'.

Source: [Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide, Life Sci 1996 (PubMed 8637402)](https://pubmed.ncbi.nlm.nih.gov/8637402/)

## 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)](https://pubmed.ncbi.nlm.nih.gov/15102092/); [α-MSH(11-13) and corneal epithelial wound models, Exp Eye Res 2006 (PubMed 16965771)](https://pubmed.ncbi.nlm.nih.gov/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](/guides/research-peptide-names-codes-and-synonyms)
-   [Which catalogue peptides are cyclic, and how are their rings formed](/guides/cyclic-peptides-in-the-catalogue-disulfide-and-lactam-rings)
-   [UK thymosin alpha-1, LL-37, KPV and ARA-290 prices](/guides/uk-immune-and-antimicrobial-peptide-prices-october-2026)
-   [Melanocortin peptides hub](/learn/topics/melanocortin-peptides)
-   [Melanotan II UK prices](/cheapest-melanotan-2-uk)
-   [PT-141 UK prices](/cheapest-pt-141-uk)
-   [KPV UK prices](/cheapest-kpv-uk)

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