Storage of lyophilised peptides

Peptides should be stored at –20°C. Most peptides, when stored at this temperature, will remain stable for several years. To minimize condensation related effects, which greatly reduce the stability of the peptide, allow the vial to gently warm to room temperature before opening. Once the required quantity of peptide is weighed out, the vial should be re-sealed immediately to prevent absorption of humidity. This is a particular problem which may be encountered with some hydroscopic peptides.

Solubility

Dissolution of peptides is the main issue, particularly with very hydrophobic peptides. The first rule is to try to dissolve the peptide in deionised water. If the peptide is insoluble, sonication may help.

Many peptides are not soluble in pure water. Addition of aqueous acetic acid (approx. 10% v/v) or mild acid such as TFA (trifluoroacetic acid, ~0.1% v/v) for basic peptides or aqueous ammonia (~1% NH4OH) for acidic peptides, followed by sonication, should resolve most of your dissolution problems. For some very hydrophobic or neutral peptides, stepwise addition of acetonitrile (from 5 to 50%), isopropyl alcohol (isopropanol), DMF or DMSO followed by sonication may also be helpful.

For peptides with stable secondary structures, it may be necessary to add chaotropic agents such as urea or guanidium.

Once the peptide is fully dissolved, the required buffer can be added to dilute the peptide to the final concentration.

Specific recommendations

Peptides containing Cysteine (C), Methionine (M), and Tryptophan (W) are particularly susceptible to oxidation and should therefore be solubilized with deoxygenated water/buffer. Deoxygenated water can be obtained either by low-pressure deaeration or by bubbling with nitrogen, helium or argon.

Do not use any basic solution or DMSO for peptides containing Cysteine or Methionine, because these solutions cause thiol oxidation, which leads to dimerisation or cyclisation.

Peptides containing an N-terminal Glutamine (Q) are susceptible to form a cyclic pyroglutamate in acid solution.

Solvents such as acetonitrile or DMSO should be diluted to a concentration compatible with the application envisaged for the peptide (e.g. cell culture…).

Confidentiality

Peptides that are synthesized are our customers’ property. The sequences and modifications are kept confidential.

Note that the service is subject to the proviso that the peptide synthesis is successful. Should Epytop encounter problems synthesizing or purifying a peptide, we reserve the right to cancel the order or to supply a product at lower yield or purity than quoted. The quoted price is hence reduced in proportion to the equivalent list price for the peptide obtained.

Peptides are for research purposes only. We are not responsible for any patent infringements that might occur with the use of these products.