How to store peptides: lyophilised powder and reconstituted solutions

How you store peptides decides how long they stay usable in the lab. A peptide is a chain of amino acids, and this chain is sensitive to heat, water, light and oxygen. A sealed vial of lyophilised powder can stay stable for years under the right conditions. The same peptide in solution can lose quality within weeks. This guide explains the storage conditions for both forms, the typical shelf life, what happens during shipping and how you recognise a degraded peptide.

Why you need to store peptides carefully

Peptides break down through a small number of chemical reactions. The most important ones are hydrolysis (the chain is cut by water), oxidation (mainly of methionine, cysteine and tryptophan), deamidation (asparagine and glutamine lose their amide group) and aggregation (peptide molecules stick together). Manning, Patel and Borchardt described these pathways in a review in Pharmaceutical Research in 1989 (DOI 10.1023/A:1015929109894). Each reaction runs faster at higher temperature and in the presence of water. Low temperature and a dry state slow all of them down at the same time.

This is the reason why research peptides are shipped as freeze-dried powder. The water has been removed, so hydrolysis and microbial growth almost stop. Lai and Topp showed in the Journal of Pharmaceutical Sciences in 1999 that peptides and proteins in the solid state still degrade slowly, and that residual moisture is the main factor that controls this rate (DOI 10.1021/js980374e). Dry storage is therefore not optional. It is the single most effective measure you can take.

How to store peptides as lyophilised powder

A sealed vial of lyophilised peptide is the most stable form you will handle. The following conditions are standard in peptide labs:

• Long-term storage: -20 °C in a freezer without automatic defrost cycles. Many labs use -80 °C for peptides that contain cysteine, methionine or tryptophan.

• Short-term storage: 2 to 8 °C in a refrigerator is acceptable for a few weeks, for example for a vial that you will reconstitute soon.

• Light: keep the vial in its box or in an opaque container. Tryptophan and tyrosine absorb UV light and can oxidise.

• Moisture: keep the vial sealed until use. Store it with a desiccant pouch if your freezer has high humidity.

Lyophilised powder is hygroscopic. It attracts water from the air. If you open a cold vial, water from the room condenses on the powder within seconds. Always let the vial warm to room temperature before you remove the cap. This takes about 15 to 20 minutes for a standard 3 mL vial.

How to store peptides after reconstitution

Once you dissolve the powder, the peptide is in contact with water and the degradation reactions start. The solvent you choose matters. Bacteriostatic water contains 0.9% benzyl alcohol, which prevents bacterial growth in a vial that is opened several times. It does not stop chemical degradation. You can read the full method in our guide on how to reconstitute peptides, and you find the solvent in our bacteriostatic water and lab supplies collection.

For a reconstituted solution the following rules apply:

• Store the vial at 2 to 8 °C in the refrigerator, never at room temperature.

• Keep the vial upright so that the solution does not touch the rubber stopper for long periods.

• Protect the solution from light. A small cardboard box in the fridge is enough.

• Write the peptide name, the concentration and the date of reconstitution on the label.

• Plan to use the solution within a few weeks. Many peptides in bacteriostatic water are commonly used within about four weeks at 2 to 8 °C. Some are more sensitive, so check the specific peptide.

Freeze-thaw cycles and aliquoting

Freezing a solution is possible, but every freeze-thaw cycle stresses the peptide. During freezing, ice crystals form and the peptide is concentrated in the small pockets of liquid between them. This changes pH and salt concentration locally and promotes aggregation. During thawing the opposite happens. One cycle is usually acceptable. Five cycles are not.

The solution is aliquoting. Divide the reconstituted peptide into small portions that match the volume you need for one experiment. Freeze the aliquots once at -20 °C or below. Thaw one aliquot when you need it and discard what is left. This method keeps the main stock from being warmed and cooled again and again. Use sterile, low-binding tubes, because peptides can adsorb to plastic surfaces. Label every tube, not only the box.

Typical shelf life when you store peptides correctly

The exact shelf life depends on the sequence. Peptides with cysteine, methionine, tryptophan, asparagine or glutamine degrade faster. Short, simple sequences last longer. The following values are typical guidelines for research peptides and not a guarantee:

• Lyophilised, sealed, -20 °C: several years

• Lyophilised, sealed, 2 to 8 °C: months to about one year

• Lyophilised, room temperature: weeks, suitable only for transport

• Reconstituted in bacteriostatic water, 2 to 8 °C: about four weeks for many peptides

• Reconstituted, frozen once as aliquots: a few months

A peptide such as BPC-157 is relatively robust in powder form. A copper complex such as GHK-Cu is also stable as powder but should be protected from light after reconstitution. The certificate of analysis gives the purity at the date of testing, not at the date of use. How to read that document is explained in our article on how to read a peptide certificate of analysis.

Shipping stability

Many researchers ask whether a peptide survives a few days in the post without cooling. For lyophilised powder in a sealed vial, the answer is usually yes. The dry state slows degradation so much that a transit time of several days at room temperature has very little effect on purity. This is why suppliers ship powder without ice packs as a rule. Place the vials in the freezer or refrigerator on the day the parcel arrives. Do not leave the parcel in a warm room, in a car or in direct sunlight.

Reconstituted solutions should not be shipped. If you must transport a solution between labs, use an insulated box with cold packs and keep the transit time short.

Signs of degradation

You cannot see most chemical degradation with the naked eye. Oxidation and deamidation change the molecule but not the appearance of the powder. Still, a few visible signs should make you stop and check:

• The powder has become a sticky film or a glassy droplet at the bottom of the vial. This points to moisture uptake.

• The powder has changed colour, for example from white to yellow.

• A reconstituted solution is cloudy, shows particles or has formed a gel. This points to aggregation or contamination.

• The solution does not dissolve completely even after gentle swirling.

• The vial seal was broken or the stopper is loose.

If you observe any of these, do not use the vial for an experiment that depends on a known concentration. Where it matters, confirm purity with HPLC. Our article on peptide purity, HPLC and mass spectrometry explains what such a test shows.

Frequently asked questions about how to store peptides

Sources

• Manning MC, Patel K, Borchardt RT. Stability of protein pharmaceuticals. Pharmaceutical Research. 1989. DOI 10.1023/A:1015929109894

• Lai MC, Topp EM. Solid-state chemical stability of proteins and peptides. Journal of Pharmaceutical Sciences. 1999. DOI 10.1021/js980374e

This article describes laboratory handling of research compounds. All products on this site are sold for laboratory research use only and are not intended for human or veterinary use.