Why Peptides Degrade: Oxidation, Deamidation and Hydrolysis
Peptides degrade mainly through oxidation, deamidation, hydrolysis and aggregation. Water, heat, light, oxygen and pH accelerate these reactions, which is why lyophilised powder stored cold and dark is far more stable than a solution.
Oxidation
Methionine, cysteine, tryptophan and histidine residues are prone to oxidation by dissolved oxygen, peroxides or light. Methionine sulfoxide adds 16 Da to the molecular mass—a shift that LC-MS can detect.
Deamidation and isomerisation
Asparagine and, more slowly, glutamine can lose an amide group, especially when followed by a small residue such as glycine. Deamidation adds about 1 Da and introduces a negative charge, and can form isoaspartate, altering structure.
Hydrolysis and aggregation
In solution, peptide bonds can slowly hydrolyse, particularly at extreme pH and next to aspartate residues. Hydrophobic sequences can also aggregate or form fibrils, reducing the amount of soluble monomer.
What this means for storage and verification
Removing water by lyophilisation slows most of these reactions dramatically. Keeping vials sealed, cold, dry and protected from light preserves them further; reconstituted solutions are the least stable form.
Degradation products have different masses or retention times, so a lot that tested well at release can still change with poor handling. Matching the lot on the vial to its report and checking handling history are part of verifying what you hold.
How to Verify Peptide Authenticity
Evidence guides
- How Peptide Lab Verification Works — How HPLC, LC-MS, content testing and lot records fit together.
- How to Verify Peptide Authenticity — A checklist for identity, lot matching and report provenance.
- How to Choose a Research Peptide Supplier — Evaluate suppliers on specifications, documentation and handling.
- Peptide Purity vs Identity vs Content — Why purity, identity and net peptide content are separate measurements.
Frequently asked questions
Which amino acids make a peptide less stable?
Methionine, cysteine and tryptophan are prone to oxidation; asparagine and glutamine to deamidation; aspartate-containing bonds to hydrolysis.
Why is lyophilised peptide more stable than solution?
Most degradation reactions need water. Freeze-drying removes it, so the powder degrades far more slowly when kept sealed, cold and dark.
What is methionine oxidation in peptides?
The sulfur in a methionine side chain reacts with oxygen or peroxides to form methionine sulfoxide, adding 16 Da to the peptide's mass—a shift LC-MS can detect.
More peptide science
- What Is a Peptide? Amino Acids, Bonds and Sequence
- How Research Peptides Are Made: Solid-Phase Peptide Synthesis
- Reading a Mass Spectrum: How LC-MS Confirms Peptide Identity
Research Use Only. Educational laboratory information; not medical advice.
