Please note that the result presented in this Peptide Calculator is only a very rough estimation of water solubility. Determining the solubility of a peptide must be done by experiment. For example, if we enter the sequence for the beta amyloid 1-40 peptide, the result will be "good water solubility". In practice, this peptide will dissolve properly at an elevated pH.
Guide to solubilising your peptide
If your application allows for it, then using an organic solvent like DMSO is a convenient way of dissolving your peptide. Once the peptide is in solution, it can be diluted further with pure water.
Most peptides will dissolve in pure water. Any buffer components that are required can then typically be added afterwards.
When a peptide won't dissolve in pure water, and organic solvents like DMSO are not an option, then there are several things to try.
- Gentle sonication
- Gentle heating
- Lowering or raising pH
When trying the latter option, shifting pH, the idea is to move away from the iso-electric point. If you have an acidic peptide, i.e. where the iso-electric point is <7 you should raise the pH, and conversely, when the pI is >7 the pH should be lowered. Taking beta amyloid 1-40 as an example again, the pI is 5.2 and as it happens this peptide dissolves at pH 9 but not at pH 7.