Handling & Storage of Peptides
All Sigma-Genosys peptides are supplied lyophilized and should be handled using the following guidelines. For maximum stability the lyophilized peptide should be stored at -20°C. Upon removal from the freezer, the peptide vial should be brought to room temperature prior to opening and weighing to avoid moisture condensation.
Initially, attempt to resuspend the peptide in sterile distilled or deionized water. If the peptide is insoluble, addition of a mild alkali such as 0.1% NH4OH can increase solubility of acidic peptides. Conversely, a mild acid such as 0.1% TFA can help solubilize basic peptides. In cases where the peptide is highly hydrophobic, it may be necessary to start with a small volume of DMF or DMSO to dissolve the peptide with subsequent additions of buffer to achieve the desired concentration. Salts tend to promote aggregation of hydrophobic peptides; consequently, it is important to add buffer salts to dilute solutions of the peptide.
Peptides containing Trp (W), Met (M), and Cys (C), are prone to oxidation and should be stored in a lyophilized state under an inert gas. These peptides should be degassed and stored in aliquots at -70°C if they will be stored in solution. Peptides containing Gln (Q) and Asn (N) are susceptible to deamidation and should be also be stored at -70°C. Additionally, peptides containing a Gln at the N-terminus will cyclize to pyroglutamate under dilute acid conditions. Most peptides without the above residues will be stable in solutions for several days at 4°C. It is best to avoid repeated freeze/thaw cycles if frozen solutions are being used.