Peptide solubility characteristics vary strongly from one peptide to another. Residues such as Ala, Cys, Ile, Leu, Met, Phe, and Val will increase the chance of the peptide being hydrophobic and dissolving in aqueous solutions. AnaSpec catalog peptides are tested for their solubility in certain solvents. This information is located on every QC Datasheet that is shipped along with the peptide. AnaSpec recommends that customers adhere to the below guideline for their custom peptides.
Peptide solubility is highly dependent on the amino acid sequence. Hydrophobic peptides (high propensity of A, F, G, V, L, I, M, W, P) in nature, will require an organic solvent to dissolve. Acidic peptides (high propensity of D, E in the peptide sequence) require a basic aqueous buffer to dissolve, while basic peptides (high propensity of K, H, and R) require an acidic aqueous buffer to dissolve.
Selection of solvent
Taking into consideration the limitations of your assay, we recommend that the following guideline be used to determine the best solvent to dissolve your peptide
To reconstitute a hydrophobic peptide, add 100 µL of DMSO and sonicate until a homogenous solution forms. Next, add your buffer of choice to form a 1 mg/mL solution (a higher concentration of peptide will require a greater amount of DMSO).
Hydrophilic (acidic) peptide
To reconstitute an acidic peptide, add 100 µL of 1% NH4OH to 1 mg of the peptide and vortex. After the formation of a clear solution, add your buffer of choice to form a 1 mg / mL solution.
Hydrophilic (basic) peptide
To reconstitute a basic peptide, add distilled water to the 1 mg of peptide and vortex.
Use and storage
Reconstituted peptides can be stored frozen at -20°C for a short time, but it is advisable to prepare multiple aliquots to avoid multiple freeze-thaw cycles. We recommend that all aliquoted solutions be lyophilized if the peptide is going to be stored for extended periods at -20 oC.
Peptides with a propensity to aggregate
For peptides that tend to aggregate due to the presence of multiple Cysteines, we recommend that these peptides be dissolved in degassed solutions and/or acidic conditions.
Additionally, some types of peptides have a propensity to form secondary and tertiary structures once dissolved. We recommend that these peptides be first dissolved in solvents such as HFIP (hexafluoroisopropanol) and then evaporated using a stream of nitrogen. The HFIP helps to break up the hydrogen bonding network that aids in forming the secondary and tertiary structures.