KPV: structure, nomenclature and handling

The sequence is lysine–proline–valine, and it corresponds to the final three residues of alpha-MSH, the thirteen-residue melanocortin peptide — positions 11 through 13, the carboxyl-terminal tail. It is worth locating that tail against the rest of the parent: the region the melanocortin receptors engage is the central histidine–phenylalanine–arginine–tryptophan motif at positions 6 through 9, and KPV sits entirely outside it. The analogues elsewhere in this catalogue that are built around that core motif are therefore structurally unrelated to this fragment beyond sharing a parent.

Each of the three residues contributes something distinct. Lysine carries a basic side-chain amine, giving the molecule its positive charge and much of its water solubility. Proline is the one amino acid whose side chain closes back onto its own backbone nitrogen, forming a rigid ring that restricts rotation — a conformational anchor even in a chain this short. Valine contributes a compact branched hydrophobic side chain. The commonly supplied form carries a free amino terminus and a free carboxyl terminus, with a molecular weight of approximately 342 daltons.

The parent peptide is amidated at its final residue, so an amidated version of this fragment also exists in catalogues. The two terminus forms differ by roughly one dalton, and the certificate's stated theoretical mass identifies which form a given batch is.

The material is catalogued as KPV, Lys-Pro-Val, and alpha-MSH(11-13), the last notation stating the fragment relationship explicitly. The free-acid tripeptide carries CAS 67727-97-3. As with most short synthetic peptides, it is typically isolated as an acetate salt, which affects the mass weighed out without altering identity.

Single-letter names collide easily, and three-letter ones especially: listings should be matched on sequence rather than on the abbreviation alone, since KPV as a string also appears in unrelated contexts. The sequence, the fragment notation and the registry number together pin the compound down unambiguously.

Mass spectrometry confirms the intact molecular mass near 342 daltons and, at the resolution routinely achieved on a molecule this small, cleanly distinguishes the free acid from the amide.

High-performance liquid chromatography resolves the main peak from related substances and yields the purity figure. A three-residue synthesis has few opportunities for deletion, so the impurity profile is usually simple. The one sequence-specific consideration is that the chain opens with a residue followed by proline: sequences beginning X-proline are prone during synthesis to diketopiperazine formation, in which the first two residues cyclize into a six-membered ring and detach, leaving truncated material. It is a known consideration for this class of sequence, and it is chromatographically visible — one more reason the trace is worth reading rather than the headline percentage alone.

One analytical property follows from the composition: the sequence contains no aromatic residues, so it has essentially no absorbance at the 280-nanometre wavelength used to quantify most peptides by ultraviolet light. Detection and quantitation instead rely on the backbone absorbance near 214 nanometres, and any certificate or in-house measurement built on 280-nanometre readings is uninformative for this compound.

HEEZ Research supplies KPV in a single format: a 10 mg lyophilized vial. There is no second strength in the current catalogue, so the format decision that arises with two-size products does not apply here.

The material is supplied as a lyophilized powder. Freeze-drying removes water and leaves the peptide as a solid, markedly more stable than the same peptide in solution, and stable enough at ambient temperature to ship without refrigeration in transit.

At roughly 342 daltons this is the lightest peptide in the catalogue, so a 10 mg vial represents a large molar quantity — a distinction that matters wherever protocols are specified in molar rather than mass terms.

Reconstitution converts the dried cake into a working solution, and it is a standard laboratory step rather than a product specification. Which solvent is used, and at what final concentration, is determined by the protocol in force at the receiving facility.

What HEEZ specifies is the contents of the vial: lyophilized KPV in a single 10 mg format, stated on the label and on the batch certificate of analysis. Where a protocol is expressed in molar rather than mass terms, the additional figure it needs is the molecular weight, which the certificate records for the batch supplied.

A charged tripeptide is about as undemanding as peptide handling gets: it dissolves rapidly in aqueous media, presents essentially no surface for aggregation, and requires no mechanical assistance. Vigorous agitation is unnecessary and avoided as a matter of routine.

Sealed lyophilized KPV is ambient-stable for the duration of transit, so no cold chain or insulated packaging is required for shipping. On receipt the vial goes to refrigeration and is kept out of direct light.

Reconstituted material is held refrigerated and used within the window the receiving facility's protocols specify, and repeated freeze-thaw cycling is avoided. Solutions are treated as short-lived relative to the lyophilized form.

By composition this is one of the most robust entries in the catalogue: no cysteine or methionine removes the common oxidation routes, no asparagine or glutamine removes deamidation, and no tryptophan removes the usual photosensitivity concern. The standard peptide handling described above is applied as a matter of discipline rather than because the molecule is fragile.

The certificate records what an independent facility measured for one specific batch. Its value lies in being batch-specific, so the first check is that the lot number on the document matches the vial in hand.

The identity section compares observed molecular mass against a stated theoretical mass, which for the free-acid form sits near 342 daltons. The stated figure also settles the terminus question described above, since the acid and the amide differ by a defined single-dalton margin.

The purity figure is the HPLC main-peak area as a percentage of total peak area, and the attached chromatogram shows how that figure was arrived at. On a sequence this short the expected picture is a clean main peak with little around it, which makes any substantial secondary peak more informative here than it would be on a long chain.

Peptide content, or net peptide content, is sometimes reported separately. It accounts for counter-ions and residual water, and it is the figure determining how much actual peptide a nominal 10 mg represents.