KPV: structure and analysis

What is KPV?

KPV is a tripeptide with the sequence lysine-proline-valine, corresponding to the C-terminal fragment of alpha-melanocyte-stimulating hormone. Three residues makes it, with GHK, the shortest compound in this catalogue.

Its relationship to α-MSH is structural: it is a fragment of that hormone's sequence, which is why it groups with the melanocortin peptides despite bearing no resemblance to the cyclic heptapeptides in that class.

The proline in the middle position imposes a conformational constraint that a more flexible residue would not.

How is KPV produced?

Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.

The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.

What are the molecular figures for KPV?

Calculated from the formula C16H30N4O4, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.

The expected ions follow from the monoisotopic mass by adding one proton per charge. They are a starting point for recognising a spectrum, not a substitute for one: adducts, salts, modifications and multiply charged species all move the observed m/z, and the certificate reports what was actually measured for a batch.

Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.

What is the sequence of KPV?

KPV is 3 residues long. Written in the one-letter amino-acid code, as the cited record states it:

The sequence is what an identity test resolves. The mass a spectrometer is compared against is the mass this chain implies, which is why a single missing or substituted residue changes the result by an amount that cannot be mistaken for instrument variation — the deletion is detectable rather than invisible.

Sequence information describes the molecule, not the material in a vial. What establishes a specific batch is the identity method and result on its certificate.

How does KPV compare with related compounds?

Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.

How is the identity of KPV confirmed?

Mass spectrometry confirms a three-residue composition. At this size the measurement is very precise in absolute terms, and any deviation from the expected mass is proportionally large.

Which impurities can appear in KPV?

The dominant analytical challenge is retention rather than resolution. A charged tripeptide is barely retained on a reversed-phase column under conditions suitable for longer sequences: it elutes close to the injection front, where it can be poorly separated from small-molecule reagent residues.

A purity method for KPV therefore has to be built for a small, basic, polar analyte. A figure produced by a generic gradient is not a reliable one, which is a good illustration of why a certificate states its method rather than only its result.

What does a certificate of analysis for KPV report?

A certificate for a batch of this material names the batch, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.

Is KPV for human use?

No. This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.

References

• MSH (11-13) — KPV — PubChem, National Library of Medicine
• Pro-opiomelanocortin — human — UniProt Knowledgebase
• Stability-indicating HPLC assay for lysine-proline-valine (KPV) in aqueous solutions and skin homogenates — Biomed Chromatogr, 2015