KPV — what changes when a peptide is only three residues
At 389 g/mol KPV sits at the small end of peptide analysis. Counter-ion is a large mass fraction, and standard peptide QC methods behave differently.
KPV is the tripeptide lysine-proline-valine, CAS 67727-97-3, molecular weight 342.43 g/mol. It corresponds to residues 11 to 13 of alpha-MSH. At three residues it sits at the small end of what peptide analysis methods are designed for, and both counter-ion mass fraction and detection behaviour differ from a typical sequence.
By the Bench Grade Research Team ·
KPV identity data
| Property | Value |
|---|---|
| CAS Registry Number | 67727-97-3 |
| Molecular formula | C19H27N5O4 |
| Molecular weight | 342.43 g/mol |
| Sequence | Lys-Pro-Val |
| Origin of the sequence | Residues 11-13 of alpha-MSH |
| Common vial size | 10 mg |
Counter-ion is a much larger share of the mass
A trifluoroacetate counter-ion contributes roughly 113 g/mol per basic site. Against a 5000 g/mol peptide that is a rounding adjustment. Against a 389 g/mol tripeptide with a lysine to protonate, it is a substantial fraction of what is in the vial.
The practical consequence is that the gap between gross vial mass and actual peptide content is proportionally wider for very small peptides than for large ones. Amino acid analysis on the COA matters more here, not less, even though the molecule is simple.
Why standard peptide QC behaves differently
- UV detection at 214 nm responds to peptide bonds. A tripeptide has two, so the signal per mole is small compared with a long sequence, and sensitivity suffers.
- There is no tryptophan or tyrosine in the sequence, so detection at 280 nm — a common secondary check — is not available for this compound.
- Short, polar peptides retain poorly on reverse-phase columns and can elute close to the void volume, where separation from small-molecule impurities is worst.
None of this makes the compound difficult to characterise. It does mean a COA showing a method developed for a large peptide, applied unchanged to a tripeptide, is worth questioning.
Solubility
With a charged lysine and no hydrophobic stretch, this tripeptide dissolves readily in aqueous solvent. Where a stubborn cake is a common complaint for hydrophobic sequences, it is rarely the failure mode here — a vial that will not dissolve points at something other than the intrinsic solubility of the compound.
A fragment that works without its parent's receptors
KPV is the C-terminal three residues of alpha-melanocyte-stimulating hormone. The parent hormone acts at melanocortin receptors; the published work on this fragment describes activity that does not require them.
That is the entire reason the fragment is studied separately rather than as a cheaper stand-in for the whole molecule. A fragment reproducing its parent's mechanism would be a manufacturing convenience. A fragment described as acting through a different route is a different research question, and cell-culture studies examine effects on inflammatory signalling pathways on that basis.
Why size opens a transport route larger peptides cannot use
At 342.43 g/mol this is among the smallest compounds sold as a research peptide, and published work examines its uptake through the PepT1 transporter in intestinal cell models.
PepT1 moves di- and tripeptides. A tripeptide fits; a fifteen-residue peptide does not, and a 43-residue protein is not in the same conversation. This is a case where molecular size is not a handling detail but the reason a particular experimental route is available at all — and it is why comparing this compound to larger peptides on a milligram basis misses what is distinctive about it.
What the KPV literature examined
Published work on this tripeptide includes cell-culture and animal studies of intestinal models and transport by the PepT1 transporter. The research library on this site links the primary sources.
References
Primary literature for the compounds discussed above. Links open the record on PubMed.
- Orally Targeted Delivery of Tripeptide KPV via Hyaluronic Acid-Functionalized Nanoparticles Efficiently Alleviates Ulcerative Colitis Xiao B, et al. Mol Ther. 2017. PMID 28456380 → · summary
- PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation Dalmasso G, et al. Gastroenterology. 2008. PMID 18061177 → · summary
Primary sources
Frequently asked questions
- What is the molecular weight of KPV?
- 342.43 g/mol, formula C19H27N5O4. It is a tripeptide — lysine, proline, valine — corresponding to residues 11 to 13 of alpha-MSH, which makes it one of the smallest compounds sold as a research peptide.
- Why does peptide content matter more for a small peptide?
- Because counter-ion mass is a fixed amount per basic site, so it is proportionally larger against a small molecular weight. The same trifluoroacetate that is a rounding adjustment on a 5000 g/mol peptide is a substantial share of a 389 g/mol one.
- Can KPV be detected at 280 nm?
- No. Detection at 280 nm relies on tryptophan or tyrosine, and this sequence contains neither. Analysis relies on peptide-bond absorbance near 214 nm, where a tripeptide gives a weaker signal per mole than a long sequence.
Compounds discussed in this guide
More on identification
- LL-37 (Cathelicidin) — identity and handling of a cationic peptide37 residues carrying an unusually high positive charge. That charge governs its solubility, its adsorption to surfaces, and why it needs different labware.
- PT-141 (Bremelanotide) — a cyclic peptide, and why that mattersBremelanotide is cyclised head-to-side-chain, not linear. The ring changes its stability, its analysis, and what a COA can and cannot confirm.
- Kisspeptin-10 — what the (45-54) in the name meansKisspeptin is a family, not a molecule. The number after the name tells you which fragment is in the vial, and the fragments differ by thousands of daltons.
All products discussed in this guide are supplied by Bench Grade Peptides for laboratory research use only. Not for human or veterinary use.