Peptide Degradation Pathways: Oxidation, Deamidation and Aggregation

Peptides are dynamic molecules. Given water, heat, light or the wrong pH they slowly change — and each change can alter results in an assay.

Chemical degradation

• Oxidation of Met, Cys and Trp residues, accelerated by light and dissolved oxygen.
• Deamidation of Asn and Gln, especially at neutral to alkaline pH.
• Hydrolysis of labile bonds such as Asp-Pro.
• Disulfide scrambling in cysteine-containing sequences.

Physical degradation

Aggregation and adsorption to container surfaces reduce the effective concentration without changing the molecule. Low-binding tubes and avoiding vigorous shaking help.

Prevention checklist

1. Store lyophilised at −20 °C, protected from light.
2. Reconstitute at an appropriate pH for the sequence.
3. Aliquot and avoid repeated freeze-thaw cycles.
4. Swirl gently rather than vortex.
5. Re-verify by HPLC for long studies.