KPV 10mg (Lys-Pro-Val)

Concentration at each diluent volume

10 mg of dry material reaches these concentrations in the volumes below. The figures are a unit conversion for preparing a laboratory stock solution, not a quantity to use.

Identity by mass: the ions to expect

An electrospray source protonates the molecule rather than weighing it neutral, so a spectrum shows a series of charge states rather than the molecular weight itself. These are the m/z values 342.43 g/mol produces, and they are what a mass spectrum on a certificate for KPV has to match.

What a certificate for KPV should carry

A purity percentage on its own is not checkable. These are the entries that make one verifiable, and their absence is the most common weakness in a research-peptide certificate.

• The chromatogram, not only the number

  A stated area percent with no trace behind it cannot be read for the shape of the main peak or for what eluted beside it. The HPLC interpreter walks through what a trace shows.

• Net peptide content, separately from gross mass

  A lyophilised peptide is a salt, usually of trifluoroacetic or acetic acid, plus residual water. The vial's stated milligrams are gross; net peptide content is the fraction of that mass which is the molecule. The two differ by ten to twenty percent routinely, and only one of them is what the price is per milligram of. The net peptide content calculator converts between them.

• The counterion, named

  Which salt form the powder is in changes the net content and the pH the powder dissolves at. A certificate that never names it leaves both unknowable.

• Water content, by a stated method

  Loss on drying and Karl Fischer water determination give different numbers, and a water figure with no method attached cannot be compared with anyone else's.

• A laboratory and a report identifier

  Without both, nothing on the document can be traced back to the laboratory that issued it. The red flag checker lists the rest.

What holds up

The degradation routes this compound is not exposed to, which is as specific a fact as the ones it is.

• No oxidation-labile side chain

  no Met, Cys or Trp in the sequence

  The three residues that oxidise readily are all absent, so the most common degradation route for a research peptide does not apply to this one. Air in the vial headspace is not the risk here that it is for a methionine-containing compound.

• No deamidation site

  no Asn or Gln in the sequence

  Deamidation is the slow clock on most reconstituted peptides, and it needs an asparagine or a glutamine to run. This sequence has neither, so time in solution does not convert it to a one-dalton-heavier, more acidic relative.

• No ultraviolet chromophore

  no Trp or Tyr in the sequence

  Photo-oxidation of peptides runs mainly through the aromatic side chains, and this sequence has none. Storing in the dark remains good practice for the excipients and the diluent, but the molecule itself has no strong absorber for ultraviolet light to act on.

• Net hydrophilic

  GRAVY -0.43

  A negative grand average of hydropathy means the side chains are on balance polar, which is the profile that stays in solution rather than associating. Freeze-thaw cycles are still worth avoiding, but this compound is not one of the hydrophobic sequences that aggregate irreversibly at an ice front.

• Solubility window

  calculated pI 10.1, net charge 1 at pH 7

  A peptide is least soluble within about a pH unit of its isoelectric point, where it carries no net charge. This one is far enough from neutral that it holds a real charge in an ordinary diluent, which is what keeps it dissolved.

• Proline-rich backbone

  1 Pro across 3 residues, 33%

  Proline's ring locks the backbone angle and gives it no amide hydrogen to donate, so a proline-rich chain is conformationally rigid and a poor substrate for the proteases that cut ordinary sequences. That rigidity is the structural reason this class of compound survives conditions that degrade a comparable peptide of the same length.