- How should I store peptides?
- How do I know if my peptide will be soluble?
- How should I solubilize my peptide?
- How should peptides be handled?
- Can I convert a free peptide into the peptide amide?
- How should I store Boc- or Fmoc-protected amino acids?
- How should I store my resins?
How should I store peptides?
Lyophilized peptides should be stored away from heat, light and moisture. Under these conditions lyophilised peptides are stable at room temperature for weeks to months, for longer term storage, peptides should be stored under the same conditions but at -20 °C.
As moisture will greatly reduce the long term stability of peptides, peptides should be allowed to equilibrate to room temperature in a desiccator before dispensing, thus avoiding exposure to moisture in the air which will condense on the peptide. Once dispensed, the peptide container should be gently purged with anhydrous nitrogen or argon, the container recapped, sealed with parafilm and stored at -20 °C.
In solution, degradation reactions could take place, the rate of which will be sequence dependent. Possible degradation reactions in solution include:
Oxidation of Cys, Met and Trp
Deamidation of Gln and Asn to Glu and Asp respectively
Oxidative cyclisation to form Cys-Cys
Peptides should not be stored in solution more than a few days. For maximum stability, peptide solutions should be frozen and stored frozen. Freeze-thaw cycling should be avoided, as this will accelerate the degradation of the peptide.
Plastic vials such as polyprolylene vials can adsorb hydrophobic peptides. Losses from dilute samples, such as mass spectrocopy samples, can be significant. Solutions of hydrophobic peptides should be stored in glass vials or non-absorbing plastic vials (A. Kraut, et al. J. Proteome Res. 2009, 8, 3778-85).
How do I know if my peptide will be soluble?
The solubility of a peptide is often hard to predict and in the more difficult cases requires multiple attempts to find the best combination of solvents and pH. Please see “How should I solubilise my peptide”
How should I solubilize my peptide?
Peptide solubility characteristics vary strongly from one peptide to another and are very difficult to predict. Residues such as Ala, Cys, Ile, Leu, Met, Phe, and Val will increase the chance of the peptide having solubility problems.
The best solvent to use will depend on the solubility properties of the peptide and solvent requirements of your assay. We recommend predicting the physical properties of the peptide, dissolving the peptide as a function of these physical properties and then adapting the solubility results experimentally.
1. From the technical datasheet note the “Charge at pH 7” parameter
2. Calculate the percentage of hydrophobic residues
A. If the “Charge at pH 7” is negative and percent hydrophobic residues is < 50 %
1. Dissolve the peptide in a minimum amount of sterile distilled water and sonicate if necessary, if it goes in solution dilute to the desired peptide concentration with assay solution
2. If not add in a dropwise fashion (50 uL) of 0.1N acetic acid in sterile distilled water to the desired peptide concentration for your assay and sonicate if necessary. Acetic acid is volatile and will be removed during lyophilization should the peptide not go into solution.
3. If the peptide still does not go into solution then lyophilise and go to procedure C
B. If the “Charge at pH 7” is positive and percent hydrophobic residues is < 50 %
1. Dissolve the peptide in a minimum amount of sterile distilled water and sonicate if necessary, if it goes in solution dilute to the desired peptide concentration with assay solution.
2. If not add in a dropwise fashion (50 uL) of 0.1N ammonium bicarbonate in sterile distilled water to the desired peptide concentration for your assay and sonicate if necessary. Ammonium bicarbonate is volatile and will be removed during lyophilization should the peptide not go into solution.
3. If the peptide still does not go into solution then lyophilise and go to procedure C
C. If the percent hydrophobic residues > 50 %
1. Dissolve the peptide in a minimum amount of acetonitrile or isopropanol. These solvents are useful for solubilising organic compounds, and can still be removed by lyophilization. If the material does not go into solution then sonicate. Once in solution dilute to the desired peptide concentration with assay solution.
2. If not dissolve the peptide in a minimum amount of DMSO or DMF. These solvents are useful for solubilising organic compounds, but due to their very high boiling points are difficult to remove by lyophilization. If the material does not go into solution then sonicate. If the peptide goes into solution dilute to the desired peptide concentration with assay solution.
3. If not then the use of chaotropic salts such as guanidine hydrochloride or urea is recommended. These will dissolve most peptides, the choice of which will depend on the compatibility with your assay system.
How should peptides be handled?
Gloves should always be worn when working with peptides to avoid contamination (e.g., enzymatic, bacterial, etc.). As many peptides are light-sensitive, they should also be protected from direct light. Repeated freeze-thaw cycles also should be avoided.
Can I convert a free peptide into the peptide amide?
Unfortunately, with few exceptions, free peptides cannot be modified, e.g. the C-terminal carboxylic group cannot be converted to a carboxamide. The peptide amide has to be synthesized de novo.
How should I store Boc- or Fmoc-protected amino acids?
Boc- or Fmoc-protected amino acids can be temporarily stored at room temperature. For long term storage, AAPPTec recommends that protected amino acid derivates should be stored tightly sealed at 5 C.
To prevent water contamination, products that have been refrigerated should be allowed to warm to room temperature before being opened.
How should I store my resins?
Resins are generally stable and can be stored at room temperature. 2-Cl-Trt chloride resin is moisture sensitive and should be stored under inert gas in a tightly sealed container.
Amino acid loaded resins should at stable at room temperature for at least 1 month. For longer storage, amino acid loaded resins should be stored at 5 C. Refrigerated containers of resins should be allowed to warm to room temperature before being opened.
