Weighing Out Lyophilized Peptides
Allow the peptide to warm to room temperature before opening the vial, to prevent condensation of atmospheric moisture onto the peptide. This ensures that it is easier to handle and weigh.
Check that there is temperature and humidity control in the laboratory. Make sure there is no draft blowing over the workspace, e.g., from an air conditioning unit. Set up sensitive weighing scales; the use of a marble slab between the scales and bench top minimizes vibrations and improves accuracy of weighing.
To avoid the effects of static electricity, use a Teflon coated spatula and weigh small amounts into an antistatic weighing boat.
Dissolve only the required amount of peptide into a buffer. The remainder of the stock should be stored dry at -20°C or -80°C.
Custom peptides can be very expensive, making it imperative that one gets as many experiments out of a sample as possible. Calculating ahead of time to determine how much peptide will be needed for the specific experiments planned and only solubilizing that much is highly recommended.
Peptides containing Cysteine, Tryptophan or Methionine are susceptible to oxidation. Once dissolved, these peptides have limited stability and long-term storage in solution is not recommended. It is advisable to blanket the dry, stock peptide with argon or nitrogen before the vial is resealed.
Hygroscopic peptides containing several charged residues (Arginine, Aspartic Acid, Glutamic Acid, Histidine, Lysine) may take up water when exposed to air. To prevent this, reseal the vial of remaining dry, stock peptide under Argon or Nitrogen. If inert gases are unavailable, then storage in a desiccator is a viable alternative. Before use, bring the sample to room temperature in a desiccator.
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