How should I reconstitute a peptide in solution?
The solubility data for catalog products can be retrieved online. To ensure peptide integrity, these recommendations should be followed:
- The peptide should be allowed to warm gradually to room temperature in a desiccator in order to minimize condensation of water vapor upon opening the vial or screw-cap bottle.
- Visually locate the peptide in the container. Tap the vial (vortex or microcentrifuge) to release any product that may have become trapped in the cap.
- Use sterile buffer or water to reconstitute the peptide. For smaller quantities such as 0.1 or 0.5 mg, it is recommended to use a sterile syringe to inject solvent into the vial as opposed to opening the cap. If DMSO is required for solubilization, be sure to use analytical grade DMSO. DMSO can degrade and become dilute with time because it can take up water from the air so care should be taken when using stock DMSO.
- Aliquot the remaining peptide solution into single-use sterile glass or high quality polypropylene vials for storage to prevent repeated freezing and thawing which can be detrimental to the integrity of the peptide.
- Store stock solution in a freezer, at -20°C or below, under dry conditions, at a pH of 5-7.
What is peptide purity?
This is the percentage of peptide that is found in the correct sequence as opposed to truncated, deleted, or incomplete sequences that can arise from peptide synthesis. The purity is determined by high performance liquid chromatography (HPLC).
What is the difference between gross peptide weight and net peptide weight?
Net peptide weight is the weight of the total peptide. Some products from the Peptide Institute are distributed in premeasured vials. These are indicated by the suffix –s or –v in the catalog. The net peptide weight is precisely determined by amino acid analysis after acid hydrolysis, HPLC, and/or UV absorption, and the value is indicated clearly on the vial label. The indicated weight is only for the net peptide molecule, and the weights of any constituents are excluded from the quantity. The amount of usable peptide meets and may exceed its advertised quantity.
Gross peptide weight is the weight of the peptide and peptide impurities as well as non-peptide components.
Peptides manufactured by Vivitide are sold in gross peptide weight.
Why does my KLH/peptide solution appear cloudy?
KLH (Keyhole Limpet Hemocyanin) is a large (MW = 4x105 - 1x107 kDa) aggregating protein. Because of its size and structure, its solubility in water is often limited. This can manifest in tendrils or a general cloudy appearance. This does not affect antigenicity, and the turbid solution can be used for immunizations.
What leads to different salt forms of peptides?
Many catalog and custom peptides are present in the trifluoroacetate (TFA) salt form. Peptides are often purified by reverse-phase High Performance Liquid Chromatography (rHPLC) using a TFA buffer. The charge on a free amine in the peptide, either on the N-terminus or in a side chain, attracts the TFA counter ion. In some cases, TFA salt is not the preference and an alternate salt form is preferred. An additional step is done by using an ion exchange column to exchange the TFA salt with a preferred salt. Some examples of alternative salt forms are acetate (-OAc) or hydrochloride (HCl). Since converting from a TFA salt form to another salt form requires an additional step, there is often an additional small fee.