How to dissolve peptides

Where possible, we provide specific solubility instructions for dissolving peptides. If specific instructions are not available, the following guidelines can be used. Most peptides are soluble in distilled water. If they do not completely dissolve, the addition of 1.0 M acetic acid for basic peptides (those containing Arg, Lys, His) or 1.0 M ammonium hydroxide for acidic peptides (those containing Asp, Glu) may help. Solubilization of extremely insoluble peptides can be assisted with 10% DMSO or DMF, although the use of these may interfere with some biological assays. Sonication can also be a useful aid for solubilizing peptides. When solubilizing peptides, it is recommended that the peptide be dissolved to the highest possible concentration, and then diluted with water or buffer to the working concentration. The buffer should only be added when the peptide is completely solubilized as salts may cause aggregation.

Net peptide weight

The majority of peptides sold by Tocris are supplied by net peptide weight. As sold, peptides may contain counterions and residual water. Therefore, although the purity of a particular peptide may be quoted as that of 98%, the net peptide content may only be 70%. To compensate for this our peptides are weighed so that the amount of peptide received is exactly that stated on the vial. For example, for 1 mg of a peptide with 70% net content, 1.43 mg of material (1/0.7) is actually supplied.

Purity of peptides

Unless otherwise stated, peptides supplied by Tocris have a purity of > 95%. Purity is assessed by HPLC, mass spectroscopy and/or amino acid analysis, with details of these available on request.

Stability and storage of peptides

Peptides are provided in lyophilized form and should be stored at -20°C. Absorption of water will decrease stability of the peptide, so insure that the product is stored in a closed, dry environment with desiccants. Avoid storing the peptide in a frost-free freezer, as changes in moisture and temperature may affect stability. Before use, and prior to opening the vial, it is recommended that the peptide be allowed to equilibrate to room temperature for at least 60 minutes. Avoid multiple freeze/thaw cycles. Long-term storage of peptides in solution is not recommended as this will reduce stability.

Peptides in solution are much less stable than in lyophilized form. This is especially true for peptides whose sequences contain amino acids such Cys, Met,Trp, Asn, Gln, and N-terminal Glu. Therefore we recommend storing peptides in solution for as short a time as possible. Avoid repeated freeze thaw cycles by dividing the peptide solution into aliquots and storing the aliquots at -20°C. Any portion of an aliquot unused after thawing should be discarded. Peptides stored in solution can occasionally be susceptible to bacterial degradation. We recommend using sterile solutions or passing the peptide solution through a 0.2 μm filter to remove potential bacterial contamination whenever possible.

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