Peptide Storage and Handling
Storage of peptides
Lyophilized (recommended): For maximum stability, peptides should be stored lyophilized at -20°C. When using refrigerated peptide, allow the vial to warm to room temperature for 30 min in a dessicator before opening the tube. Many peptides are hygroscopic and may take up some atmospheric water upon opening the vial.
Dissolved peptides: Peptides in solution are much less stable compared with lyophilized peptides. And we recommend the following for optimized stability and storage of dissolved peptides:
- Store at -20°C in a sterile slightly acidic, buffered solution (pH 5-7).
Keep in mind :
- cyclic peptides, like lactams will re-open under particular conditions (pH value, temperature, bacteria contamination).
- Disulfide bridges (R-S-S-R) are prone to redox reactions (R-S-H + H-S-R).
- Amino acids like Tryptophan (W) will be prone to oxidation / degradation (Kyurenine Pathway) in the presence of Fe2+ / H202 . Store peptides under inert gas atmosphere.
- Aliquot your stock solution and avoid repeated thawing and freezing cycles.
The solubility of peptides in aqueous solutions greatly depends on primary and secondary structures. In addition many modifications may affect solubility. For example C-amide and N-acetyl termini will significantly decrease the solubility of any sequence. For purification purposes, most peptides would dissolve in polar solvents (acetonitrile, methanol, propanol, DMF, DMSO), and some will affect retention times in reversed-phase LC.
The following experimental approaches will help you reconstitute your peptides.
Always use sterile water to dissolve peptides, as most bacteria will hydrolyze peptides very efficiently. Generally speaking it is recommended to first dissolve your peptide in water and further dilute with buffered /salts working solution. The recommended concentration for peptides with unknown solubility is 1-10 mg/ml. For difficult to dissolve peptides, the following basic rules may help, with or without a brief sonication.
- Basic peptide (presence of lys, arg…): one may try 1-10% acetic acid.
- Acidic peptide (presence of glu, asp,…): one may try 1% ammonium hydroxide or 1-10% ammonium bicarbonate.
- In case of aggregation and/or hydrophobic peptides (aliphatic chains or aromatic amino acids) one may introduce organic polar solvents to aid breaking hydrophobic intermolecular interactions. While several solvents would work, we recommend DMSO/water or DMF/water. Once fully solvated, you may dilute your peptide using sterile water or buffered aqueous solutions to reach the working concentration.
Cysteine, methionine, tryptophan are prone to oxidation and should be dissolved and stored in oxygen-free water, obtained by bubbling nitrogen, helium or argon in water before dissolution.
KLH conjugates may prove difficult to dissolve in water and it may take a long time to fully hydrate and still exhibit a turbid solution.