Handling lyophilised peptides in the laboratory: stability basics

Powders: keep them dry

Freeze-dried peptides are hygroscopic and absorb water from the air. Moisture speeds chemical degradation, so vials are best allowed to reach room temperature before opening, to avoid condensation forming on the cold powder, and resealed promptly.

Temperature and light

Cooler is generally better for long-term storage of powders, and light-sensitive residues such as tryptophan are better protected in the dark. The exact conditions depend on the peptide, so the supplier's documentation takes priority over general rules.

Which residues are vulnerable

Sequences rich in these residues are the ones most likely to show degradation on storage.

• Methionine and cysteine: prone to oxidation.
• Asparagine and glutamine: can deamidate.
• Aspartic acid sequences: can undergo rearrangement.
• Tryptophan: sensitive to light and oxidation.

Solutions are different

Once dissolved, a peptide is exposed to hydrolysis, microbial growth and repeated freeze-thaw damage, and its stability drops sharply compared with the powder. Preparing only what an experiment needs, and avoiding repeated freezing and thawing, are the standard precautions.