Peptides can have widely varying solubility properties, depending largely on their primary sequence. While many peptides dissolve easily in water, some, especially those containing multiple hydrophobic amino acid residues, may not readily dissolve. As a general procedure, we recommend first attempting to reconstitute peptides in sterile, distilled water, with sonication if necessary. If solutability is still a problem, addition of a small amount of dilute (approximately 10%) aqueous acetic acid (for basic peptides, PI < 7) or aqueous ammonia (for acidic peptides, PI >7) may facilitate dissolution of the peptide. If solubility issues still persist, it is likely to be a highly hydrophobic peptide, and may require an organic solvent such as Acetonitrie, DMF, or DMSO in order to get the peptide into solution. It may be desirable, initially, to determine solutability on an aliquot of the total sample. The buffer of choice for your experiments should only be added after the peptide is fully in solution, since salts may promote aggregation and therefore create solubility problems.
Lyophilized peptides generally have excellent stabilities (in most cases, can be stored for years at -20ºC or lower temperatures with little or no degradation), but, in solution, they generally have much more limited stabilities. Since peptides are susceptible to degradation by proteases of bacterial or microbial origin, the first rule is to prepare sterile solutions, either by reconstitution in sterile, distilled water, or by sterile filtration after reconstitution. For peptides which contain methionine, cystenic or tryptophan residues, oxidation may generate impurities with or without concomitant biological inactivation. To avoid this, peptides containing these amino acids should be dissolved in oxygen-free solvents.
|Amino Acid||3-Letter Code||1-Letter Code||Molecular Weight||Hydropathy|
|Asaragine or Aspartic acid||Asx||B||132.61||1.0|
|Glutamine or Glutamic acid||Glx||Z||146.64||1.0|