The Three Enemies of Peptide Stability
Peptides degrade through three primary mechanisms. Understanding these helps you create the ideal storage environment:
- Moisture (Hydrolysis) — water attacks the peptide backbone, breaking bonds and fragmenting the molecule
- Oxygen (Oxidation) — amino acids like cysteine, methionine, and tryptophan are particularly vulnerable to oxidation damage
- Heat (Thermal Degradation) — higher temperatures accelerate all degradation reactions
Light exposure can also damage certain peptides, particularly those containing tryptophan or tyrosine.
Storing Lyophilized (Freeze-Dried) Peptides
Lyophilized peptides are the most stable form and can last for years when stored properly:
Temperature
- -20°C (-4°F) — standard for most peptides, good for 2+ years
- -80°C (-112°F) — preferred for expensive or unstable peptides, or those with disulfide bridges
- +4°C (refrigerator) — acceptable for short-term storage (weeks), not ideal for long-term
Never store lyophilized peptides at room temperature for extended periods.
Moisture Protection
Even in a freezer, moisture can accumulate over time. For maximum protection:
- Keep peptide vials inside a sealed secondary container (glass jar with lid, or zip-lock bag)
- Add silica gel desiccant packets to absorb any moisture that enters
- Replace desiccants periodically (when they change color, if indicating type)
Light Protection
Use amber vials when possible, or wrap clear vials in aluminum foil. Most freezers are dark anyway, but this provides an extra layer of protection.
Storing Reconstituted Peptides
Once dissolved in liquid, peptides are much more vulnerable to degradation:
Refrigerated Storage (Recommended)
- With bacteriostatic water: 3-4 weeks at 2-8°C
- With sterile water: 24-48 hours at 2-8°C (use quickly or aliquot and freeze)
Frozen Aliquots (Long-Term)
For long-term storage of reconstituted peptides, divide the solution into single-use aliquots:
- Immediately after reconstitution, divide the solution into small volumes (50-100μL each)
- Use sterile tubes designed for low-temperature storage (PCR tubes or LoBind Eppendorf tubes)
- Freeze at -20°C or -80°C
- When needed, thaw ONE aliquot, use it, discard any remainder
- Never re-freeze a thawed aliquot
The Freeze-Thaw Problem
Each freeze-thaw cycle damages peptides. Ice crystals can physically disrupt molecular structure, and the concentration changes during freezing/thawing stress the molecules. Aliquoting into single-use portions is the only way to avoid repeated cycles.
Signs of Peptide Degradation
How do you know if your peptide has gone bad?
- Color change — most pure peptides are white or off-white; yellow or brown indicates degradation
- Unusual odor — peptides should have little to no smell
- Solubility changes — if a previously soluble peptide now won't dissolve, it may have aggregated
- Reduced activity — in your research results, if the peptide seems less effective than expected
When in doubt, test a small amount before committing to a full experiment, or order fresh material.