Peptides and Proteins

Handling and Storage Guidelines for Peptides and Proteins

  1. The product vial should be tightly capped at all times when not in use.
  2. While some peptides and proteins are stabile at 4 °C, we recommend –20 °C for short-term storage (1–2 weeks) and –80 °C for longer storage. It is always advisable to store away from bright light.
  3. Exposure to moisture will greatly decrease the long-term stability. Before using the peptide, remove from cold storage and allow the peptide to equilibrate to room temperature before removing the lid of the container. This will reduce the uptake of moisture that is present in the surrounding atmosphere.
  4. Peptide sequences containing C, M, or W are prone to air oxidation. All cysteine-containing peptides will slowly oxidize with time, the rate of which is largely dependent on the sequence and storage conditions. It is recommended to purge the air out of the vial and replace it with a blanket of nitrogen or argon.
  5. When known, Sigma® will supply the solubility information on the Product Detail page or on the Certificate of Analysis. In the event solubility information is not known, we recommend following our peptide solubility guidelines.
  6. When preparing a working stock solution, make a solution that is at a higher concentration than required for the experimental assay by dissolving the peptide in sterile distilled water or sterile dilute acetic acid (0.1%), where applicable. The stock solution peptide can be diluted further with the assay buffer. If the peptide does not dissolve in water or acetic acid, the peptide solution can be lyophilized without any nonvolatile residues. Once the peptide is lyophilized, other stronger solvents can be tried (see step 5).
  7. Repeated freeze-thaw cycles should be avoided for both lyophilized peptides and peptide solutions. If peptide samples need to be frequently or periodically taken from the stock, it is recommended to make a series of working aliquots from the stock.
  8. In general, peptide solutions are stable for up to a week at 4 °C. However, if the peptide sequence has inherent instability, it might be better to freeze the solution when not in use. Peptide solutions at pH>8 should also be frozen when not in use.
  9. The shelf life of peptide solutions is limited. Peptides containing N, Q, C, M and W are unstable when stored in solution. Using sterile buffers (pH 5–6) and freezing the aliquots will prolong the storage life of the peptide. Storage at –20 °C or colder is optimal.
  10. The most effective way to prevent or minimize peptide degradation is to store the peptide in lyophilized/powder form at –20 °C or preferably at –80 °C. If the peptide is in solution, freeze thaw cycles should be avoided by freezing individual aliquots. Exposure to pH>8 should be avoided. However, if it is necessary to dissolve peptides at pH>8, the solutions should be chilled. Finally, prolonged exposure of lyophilized peptides and solutions (especially at high pH) to atmospheric oxygen should be minimized.

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