STORAGE OF LYOPHILIZED PEPTIDES
All products marked “keep cool and dry” should be stored frozen, preferably at -20°C. Most peptides, when stored below -10°C, will remain stable for several years. Storage in buffer is not recommended. We could provide the peptide in aliquots for you.
When using a frozen product, the bottle or vial should be allowed to warm to room temperature in a desiccator containing fresh desiccant before opening. This process can take an hour or more from -20°C, depending on the pack size. Failure to do this can cause condensation to form on the product when the bottle or vial is opened and will greatly reduce the stability of the material. Once opened, the required quantity should be weighed out and the vial or bottle re-sealed immediately to prevent absorption of water.
Solubilization of Peptides
Use only a small amount of peptide to test for solubility. Only when the peptide has been fully dissolved, should the buffer salts be added and the solution diluted to its final concentration.
- The main problem associated with the dissolution of a peptide is the formation of aggregated secondary structures. Although this is more pronounced with hydrophobic peptides, it is liable to occur with all except the shortest peptides, irrespective of polarity. Therefore, the first rule is to try to dissolve the peptide in sterile, distilled or deionized (and if possible, oxygen-free for peptides containing cysteine, methionine, tryptophan) water.
- If the peptide is insoluble in pure water, sonication may help break up any particles and increase the rate of dissolution, though sonication can cause warming of the solution and degradation of the peptide.
- To recover this first sample of peptide, use lyophilisation.
- If the peptide contains many basic amino acids, use an aqueous acetic acid (1 to 10 %) solution, with or without sonication. For very hydrophobic peptides, use a 50 % aqueous acetic acid.
- If the peptide has many acidic amino acids, use an aqueous ammonia (1 to 10 %) solution, or a volatile basic buffer (up to pH 8) such as N-ethylmorpholine acetate or bicarbonate, with or without sonication. The pH may have to be adjusted before chromatography.
- Propanol and acetonitrile can dissolve some medium-sized peptides. If the peptide is to be injected onto a column, the amount of organic solvent, especially propanol, must be kept small, or retention time will be greatly affected.
- If the peptide is highly hydrophobic with aromatic or hydrocarbon-like side chains, such as valine, leucine, isoleucine, methionine, phenylalanine, tyrosine, alanine or if the peptide is neutral, use a chaotropic agent such as DMF or DMSO, added drop by drop until the peptide dissolves.
- If the peptide does not dissolve with the above organic solvent, it may require TFA or formic acid
- High concentration of chaotropic salts helps to dissolve the peptide by breaking up the secondary structures.
- Chaotropic agents are suitable for preparing solutions for analysis, but may interfere with a biological system used for the study of the peptide.
- With reverse-phase chromatography, the DMF will elute with the buffer front.
STORAGE OF PEPTIDES IN SOLUTION
Peptides in solution are much less stable than lyophilized peptides. If you need to store peptides in solution, follow these guidelines for best results:
- It is recommended that the stock solution be aliquoted upon arrival to prevent degradation caused by repeated thawing and freezing. Thaw only what is needed and discard any unused portion.
- Sterile filter before storing to prevent bacterial contamination.
- Maintain peptides in an oxygen-free environment as peptides containing cysteine, methionine, tryptophan, glutamine and asparagine are susceptible to oxidation and have limited shelf life.
Peptides have a wide range of properties, which the above guidelines may not address.