Peptide reagents and drugs should ideally be stored in a dry environment. Freeze-dried peptides can be kept at room temperature, but it's important to avoid exposure to air to minimize humidity's impact. If freeze-drying isn't an option, it's best to store peptides in small working volumes to reduce exposure to air.
For peptides containing cysteine (Cys), methionine (Met), or tryptophan (Trp), using a deoxidation buffer is crucial when dissolving them, as these peptides are prone to oxidation. To further prevent oxidation, flowing nitrogen or argon over the peptide reagent before sealing the container can help.
Peptides with glutamine (Gln) or asparagine (Asn) are also sensitive and can degrade easily. In general, peptides have a limited shelf life, especially those containing these reactive amino acids.
Solubility can vary greatly among peptides. Insolubility often results from the formation of secondary structures, which is especially common in peptides with multiple hydrophobic residues. Salt can promote secondary structure formation, so it's recommended to first dissolve peptides in sterile distilled or deionized water. If solubility is still an issue, sonication can be helpful. If necessary, a small amount of dilute acetic acid (10%) or ammonia can be added to aid dissolution.
For long-term storage, freeze-drying is the best method. Freeze-dried peptides can be kept at -20°C or lower for several years with minimal degradation. Peptide solutions, however, are much less stable and are susceptible to bacterial degradation, so they should be dissolved in sterile purified water.
Peptides containing methionine, cysteine, or tyrosine have a limited shelf life due to oxidation, and should be dissolved in an anaerobic environment. To prevent degradation from repeated freeze-thaw cycles, it's recommended to dissolve only the necessary amount for immediate use, and store the remaining peptide as a solid.
