Peptide manufactures normally deliver the peptides either in lyophilized form or as aliquots in solution. To ensure stability of the peptides, proper storage and handling is imperative and below is a brief guide to show how to do this-:
Storage guidelines for peptides in solution
The shelf-life of peptides stored in solutions is not very long. This is especially true if the peptides have sequences which contain Trip, Met, Gln, Cys and N-terminal Glu. Additionally, peptides stored in solutions are prone to bacterial degradation hence many manufacturers never recommend storing peptides in solutions.
However, if storing the peptides in solutions is completely unavoidable, remember to use sterile buffers at pH between 5 and 6 to dissolve the peptide. Then divide the peptide solutions in aliquots and store at -200C. Do not freeze-thaw cycles of the aliquots as this might end up degrading the peptides. Feel free to pass the peptide solution through an appropriate filter to remove any bacterial contamination from the solution. If you end up dissolving too much of the peptide, re-lyophilization may help in maintaining the stability of the excess peptide.
How to store lyophilized peptides
The stability of each peptide is always unique and dependent upon its sequence. Lyophilized peptides should be stored away from bright sunlight and at temperatures of about -200C. Under these conditions, lyophilized peptides will remain stable for many years, however, certain residues of amino acids in the peptide sequence may not remain stable for such a long time. Peptides with His, Lys, Glu, or Asp are susceptible to moisture absorption from the atmosphere and they should be stored with a dessicator in a tightly closed vial.
Additionally, peptides subjected to freeze-thaw cycles may get degraded. Whenever possible, you should pre-determine the amount of peptide needed for each experiment set and the peptides should be aliquoted in separate vials accordingly. By aliquoting, the number of freeze-thaw cycles will be reduced, thus reducing the exposure to air by the peptides.