KPV

What KPV is, structurally

KPV is a tripeptide, three residues with a free N-terminal amine and a free C-terminal acid. At 342.44 g/mol it is one of the smallest compounds in this catalogue.

The formula reconciles exactly. Four nitrogens across three residues means three backbone amides plus one side-chain nitrogen, and lysine's epsilon-amino group is the only candidate. The four oxygens are two backbone carbonyls plus the terminal acid. Nothing is left over.

Charge runs opposite to most short peptides here. Lysine's epsilon-amino group stays protonated across the ordinary working range, the N-terminal amine adds a second positive charge, and the only negative is the C-terminal acid, so KPV is net cationic where the Ala-Glu-Asp family is strongly anionic. It is polar and water soluble, though no quantitative figure is quoted here.

Proline at position two is the consequential residue. Its side chain loops onto its own backbone nitrogen, removing the amide hydrogen and restricting rotation, so the chain is stiffer than three residues suggest. It also puts a lysine-proline bond at the N-terminus, which drives the compound's main instability, covered below.

There is no cysteine, no methionine, no aromatic residue and no acidic side chain anywhere in the sequence.

Reconstitution and handling

Sterile water is the default solvent, and with no metal centre present PBS or an appropriate assay buffer are equally reasonable. Add diluent down the vial wall, swirl gently, and let it stand until clear. Vortexing serves no purpose on a peptide this small.

Prepare solutions near neutral and use them promptly. Alkaline conditions accelerate the cyclisation described below, which begins with an unprotonated N-terminal amine, and raising the pH is what deprotonates it.

Adsorption is worth allowing for at low concentration, with low-protein-binding tubes reducing measured loss. Being cationic rather than anionic, this peptide binds negatively charged surfaces such as untreated glass more readily than polypropylene.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial warm before opening. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly.

What makes this compound unusual is that almost none of the standard peptide liabilities apply. No cysteine to oxidise, no methionine to form a sulfoxide, no tryptophan to photo-oxidise, no asparagine or glutamine to deamidate, no aspartate to isomerise. On composition alone this looks exceptionally stable.

One route remains, and it comes from arrangement rather than composition. A proline at position two with a free N-terminal amine ahead of it is the classic setup for diketopiperazine formation: the amine attacks the second peptide bond, closing a six-membered ring across the first two residues and cleaving the third away. Here that gives cyclo(Lys-Pro) at 225.29 and free valine at 117.15, together accounting for the parent 342.44 exactly. Proline promotes it more than any other second residue, its ring already holding the backbone near the required geometry.

The practical control is the same either way: dry, cold and near-neutral.

These are storage conditions for the material, not dosing or administration guidance.

How KPV is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. With no aromatic residue in the sequence there is no 280 nm absorbance, so detection sits near 214 nm. The peptide is small, polar and cationic, so it retains weakly on a standard C18 column and elutes early, and ion-pairing conditions matter more here than for a neutral or acidic peptide.

Area percent is a chromatographic measure rather than peptide content by weight. Solid-phase synthesis delivers a salt, usually trifluoroacetate or acetate, and on a 342 g/mol peptide with two basic sites that counter-ion is a proportionally large share of the vial contents. Residual trifluoroacetate and deletion sequences are the impurity classes to resolve.

Mass spectrometry confirms identity and, unusually for a short peptide, reads the degradation route directly. Diketopiperazine formation is not isobaric, so the products appear at 225.3 and 117.2 against a parent of 342.4. That is an unambiguous signature, and it makes this compound easier to assess than sequences whose main liability leaves the mass unchanged.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

Why does a proline at position two matter? Because it sets up diketopiperazine formation. The free N-terminal amine can attack the second peptide bond and close a six-membered ring across the first two residues, cleaving the third off. Proline favours this more than any other residue in that position, since its ring already constrains the backbone toward the required geometry.

Is the main degradation route visible by mass spectrometry? Yes, and that is not true of most peptides. The ring closure cleaves the molecule, so the products differ in mass from the parent: 225.3 and 117.2 against 342.4. Nothing here is isobaric with the intact compound.

Full specifications for KPV.