Selank is a small synthetic peptide, which makes it comparatively easy to characterise. That is useful for a laboratory: there is little excuse for incomplete documentation. This profile covers the molecule and its paperwork for in vitro research use.
The molecule
Selank is a heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues are the natural tetrapeptide tuftsin, and the Pro-Gly-Pro extension was added to slow enzymatic breakdown. Its molecular weight is about 752 Da.
It contains no cysteine, methionine or tryptophan, the residues most prone to oxidation, so it is chemically more forgiving than many longer peptides. It is still a peptide in solution, with the usual limits on working life.
What the certificate should show
For a seven-residue peptide a complete certificate is straightforward to produce:
- Identity by mass spectrometry, agreeing with the expected mass of about 752 Da.
- Purity by RP-HPLC with the chromatogram shown.
- The salt form, usually acetate, since the counter-ion contributes to the weighed mass.
- Batch number, testing laboratory and date.
Net peptide content
Short, basic peptides such as Selank carry counter-ions and bound water, so the weight in the vial is not all peptide. Where a certificate gives net peptide content, use it when you calculate molar concentrations. Where it does not, note in your records that concentrations are based on gross weight.
Handling
Store the lyophilised vial as the batch label directs, generally cold, dry and sealed. Selank is freely soluble in water. Once reconstituted, keep it refrigerated, avoid repeated freeze-thaw cycles, and record the preparation date on the vial.