Are KPV and MT-2 related?

Yes — both derive from alpha-MSH, but from opposite halves. KPV takes the anti-inflammatory C-terminus, MT-2 the receptor-binding core.

Why is MT-2 three times larger?

Receptor binding needs enough structure to present a specific surface. Three residues cannot do it; a constrained ring can.

Neither. A third alpha-MSH derivative, afamelanotide, is approved — but that is a different molecule from both.

MT-2 (Melanotan II)

Two Compounds, One Parent, Opposite Intentions

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-234 cited sources

Alpha-MSH has two functionally separable activities — pigmentation through melanocortin receptors, and anti-inflammatory activity at its C-terminus. KPV isolates the second and discards the first. MT-2 is built around the first. They are opposite halves of one hormone.

Key facts

Shared parent: alpha-MSH, 1,664.9 Da
KPV: C-terminal tripeptide, 342.43 Da
KPV keeps: Anti-inflammatory activity
MT-2: Cyclic heptapeptide, 1024.2 Da
MT-2 keeps: Receptor-binding core
Both unlicensed: Yes

The hormone that does two things

Alpha-MSH drives pigmentation through melanocortin receptors and separately carries anti-inflammatory activity localised to its C-terminal end. Brzoska and colleagues titled their 2010 chapter terminal signal for exactly that reason. Two activities in different regions of one thirteen-residue peptide.

How the two derivatives split it

KPV takes the last three residues — Lys-Pro-Val — keeping the anti-inflammatory activity and dropping the receptor-binding core entirely. MT-2 does the reverse, compressing the receptor-binding portion into a constrained ring and dropping the C-terminal tail. Each is defined by discarding what the other retained.

Research material referenced

MT-2 10mg — third-party HPLC tested

View — £19.99

Why the size difference is so large

KPV at 342.43 Da is three residues with no modifications. MT-2 at 1024.2 Da is seven residues plus a lactam bridge, a D-amino acid, a non-standard residue and two capped termini. Three times the mass, because receptor engagement requires a specific three-dimensional presentation that three residues cannot provide.

What that says about fragment design

The activity you want determines how much molecule you need. An effect that runs through diffuse intracellular signalling can survive extreme truncation. An effect that requires binding a specific receptor pocket needs enough structure to present the right surface — which is why MT-2 is cyclised and constrained while KPV is a bare tripeptide.

Where they sit in this catalogue

Both are unlicensed everywhere. Both descend from a hormone whose other derivative — afamelanotide — is an approved medicine. Neither is that medicine. Reading them alongside each other is the clearest illustration on this site of how one parent molecule produces entirely different compounds depending on which of its functions is being pursued.

Extended research context

The MT-2 (Melanotan II) deep dive

Deep dive: the identifier collision that points the wrong way

This site has now found several plausible-looking identifiers that resolve to the wrong molecule. A PubChem record for tirzepatide cited as retatrutide. Thymosin beta-4's CAS quoted as TB-500's. An unrelated organic acid returned for KPV. This one is the most consequential of the set, and the reason is direction. Searching PubChem for melanotan returns CID 16197727 - afamelanotide, at 1,646.8 Da for C78H111N21O19. That is Melanotan I, a linear thirteen-residue peptide, and it is an APPROVED MEDICINE, marketed as Scenesse for erythropoietic protoporphyria. Melanotan II is CID 92432: cyclic, seven residues, 1024.2 Da, 622 Da lighter, and assessed by no regulator anywhere. So the wrong record does not merely mislead about mass. It resolves from an unlicensed compound toward a licensed one, and the sequential naming - I and II - makes them look like versions of a single product rather than the structurally distinct compounds they are. Anyone verifying a certificate by searching the bare name lands on an approved drug's record and may never notice which compound it names.

Deep dive: four stability features in seven residues

PubChem's IUPAC name for CID 92432 is unusually complete and reads as a full specification: N-acetyl-L-norleucyl-L-alpha-aspartyl-L-histidyl-D-phenylalanyl-L-arginyl-L-tryptophyl-L-lysinamide, cyclic (2-7)-peptide. Unpack it and there are four independent protease-resistance features in a molecule of seven residues. A lactam bridge joins the aspartate side chain at position 2 to the lysine side chain at position 7, closing the ring - which both locks conformation for receptor engagement and eliminates the free termini exopeptidases require. Position 4 is D-phenylalanine, the mirror image of the natural form, and proteases are stereospecific enough that they largely cannot process it. The N-terminus is acetylated and the C-terminus amidated, capping both ends. And position 1 is norleucine, which is not among the twenty proteinogenic amino acids at all - so even setting aside the cyclisation and the D residue, this peptide could never have been a gene product. It is a fully synthetic construction rather than a modified natural sequence, and it is among the most chemically robust compounds in this catalogue as a direct result.

Deep dive: why the safety literature is included rather than omitted

There is a published dermatological literature here, and the editorial choice was to state it. Reid and colleagues documented atypical melanocytic naevi following melanotan injection in the Irish Medical Journal in 2013. Eijmael and colleagues published a risk review in the Nederlands Tijdschrift voor Geneeskunde in 2022 - a national medical journal considering the topic worth addressing directly. Case reports have a real limitation: they establish an observation without a denominator, so they cannot establish causation or incidence, which is the same constraint that applies to pharmacovigilance disproportionality signals. But that limitation cuts both ways. A case report is not proof of harm and it is not dismissible either. What makes the absence of better data significant here is that no regulator has assessed this compound - so there is no label, no contraindications, no adverse event reporting requirement and no monitoring framework. The information that would normally exist for an injectable product simply does not, and what is available instead is what individual clinicians chose to publish after seeing something. Presenting the compound without that context would give an incomplete picture of what is actually known.

Research applications

▸Melanocortin receptor pharmacology and selectivity research
▸Cyclic peptide and lactam bridge design studies
▸D-amino acid substitution and protease resistance research
▸Structure-activity work on constrained peptide analogues
▸Comparative work on alpha-MSH derivatives
▸Analytical method development for cyclic peptides

Handling checklist

✓Verify against CID 92432, 1024.2 Da, C50H69N15O9, CAS 121062-08-6
✓Never verify by searching 'melanotan' alone - that returns afamelanotide at 1,646.8 Da
✓Require stereochemistry on the certificate - D-Phe4 is not detectable by mass
✓Protect from light; tryptophan at position 6 is photochemically reactive
✓Store lyophilised, cold, dry and dark
✓Expect no disulfide or oxidation satellites - no cysteine, no methionine
✓Quantification at 280 nm is available thanks to the tryptophan

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Searching PubChem for 'melanotan' to verify identity

Fix: That returns CID 16197727, afamelanotide, at 1,646.8 Da - an approved medicine and a different molecule. Use CID 92432 or search Melanotan II with the numeral.

✗ Treating Melanotan I and II as versions of one compound

Fix: They differ by 622 Da, by six residues, and by whether the peptide is cyclic or linear. Only Melanotan I has been assessed by regulators.

✗ Reading afamelanotide's approval as covering MT-2

Fix: Different molecule, different structure, different evidence, different assessment. Nothing transfers.

✗ Accepting a sequence written without stereochemistry

Fix: L- and D-phenylalanine have identical mass. A peptide with the L form at position 4 is a different compound that mass spectrometry cannot distinguish.

✗ Assuming a non-selective agonist affects only its intended receptor

Fix: Five melanocortin receptors share binding surfaces across different tissues. Engagement elsewhere is the same pharmacology in another place, not a side reaction.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Are KPV and MT-2 related?: Yes — both derive from alpha-MSH, but from opposite halves. KPV takes the anti-inflammatory C-terminus, MT-2 the receptor-binding core.
Why is MT-2 three times larger?: Receptor binding needs enough structure to present a specific surface. Three residues cannot do it; a constrained ring can.
Is either approved?: Neither. A third alpha-MSH derivative, afamelanotide, is approved — but that is a different molecule from both.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

How we write and check this content Report a factual error in this article

More MT-2 (Melanotan II) articles

Popular across the research hub

One flagship guide from every other research category — keep exploring.

← Back to Forum