Handling and Storage of Synthetic Peptides
1. How should I store and handle my synthesized peptides?
Peptide storage guidelines: Peptides should be stored in lyophilized form at -20°C or preferably at -80°C in a sealed container with desiccant in order to minimize peptide degradation. Under these conditions, the peptide can be stored for up to several years and the following activities can be prevented such as bacterial degradation, secondary structure formation, and oxidation.
Open the package: It is better to equilibrate the peptides to room temperature in a desiccator prior to opening and weighing. Failure to warm up beforehand can cause condensation to form on the product when the bottle is opened and this will reduce the stability of the peptide products.
Weigh peptides: Weigh out you needed quantity of peptide quickly and store all unused peptide at -20°C or less. Sequences containing cysteine, methionine, tryptophan, asparagine, glutamine, and N-terminal glutamic acid will have a shorter shelf life than other peptides.
2. How should I dissolve peptides?
It is necessary for you to test a portion of the synthesized peptide first before dissolving the entire peptide sample. You may need to test different solvents until you find an appropriate one. It is necessary to sonicate the peptide solution because sonication enhances solubilization.
- If the peptide is acidic, add 0.1M ammonium bicarbonate to dissolve the peptide and add water to the desired concentration.
- If the peptide is basic, add 25% acetic acid to dissolve the peptide and add water to the desired concentration.
- If peptides are still insoluble, add acetonitrile to 20 %(v/v), and sonicate the sample.
- If, after sonication, the peptide has not dissolved completely, lyophilize and remove the volatile buffer solution such as water, acetic acid or acetonitrile. When the sample is completely dry, dropwisely add DMF or DMSO until the peptide dissolves. Slowly dilute the solution with water to approximately 10% (v/v) DMF or DMSO. Dilute the stock solutions to the same peptide concentration.
- In order to prevent or minimize peptide degradation, store the peptide in lyophilized form at -20°C or preferably at -80°C. If the peptide is in solution, freeze thaw cycles should be avoided by freezing individual aliquots.
3. How should I choose the peptide purity for my research?
LifeTein recommends the following peptide purity for your research:
>70% purity
- Peptide array.
- Antigen for antibody production.
- Competitive elution chromatography.
- ELISA standard for measuring antisera titers.
>80% purity
- Affinity purification.
- Phosphorylation assays.
- Protein electrophoresis applications and immunocytochemistry.
- Non-quantitative enzyme-substrate studies.
- Non-quantitative peptide blocking studies.
>95% purity
- Quantitative ELISA standards and RIA protocols.
- Quantitative receptor-ligand interaction studies.
- In vitro bioassays and in vivo studies.
- Quantitative enzyme studies and blocking assays.
- NMR studies.
- Mass spectrometry.
- Quantitative assays.
>98% purity
- SAR Studies
- Clinical trials
- API (Active Pharmaceutical Ingredients)
- Commercial products
- X-Ray crystallography studies
4. What is peptide purity?
Peptide purity is the amount of the target peptide as determined by HPLC at 214 nm, where the peptide bond absorbs. Other impurities can also be found in the content includes deletion sequences, truncated sequences, and incompletely deprotected sequences. Peptide purity does not include water and salts in the sample.
5. How are peptides synthesized?
Unlike the natural protein synthesis, peptide is synthesized from the C to N terminus. Peptide synthesis at LifeTein is performed by PeptideSyn technology based on Fmoc or t-Boc chemistry to protect the alpha amino group. The deprotection agent (piperidine for Fmoc, TFA for Boc) frees the alpha amino group in preparation for coupling the next amino acid in the sequence, revealing a new N-terminal amine to which a further amino acid may be activated by one of several reagents and a peptide bond is formed. When the synthesis is finished, peptides are cleaved from the resin and de-protected. Peptides are then precipitated, washed, and then lyophilized.
6. What are your QC standards on my peptide synthesis?
All materials supplied to LifeTein are considered the confidential property of the customer. LifeTein provides HPLC and MS in your package. Peptides are purified by reversed phase chromatography if the QC data do not meet the purity criteria. All synthetic peptide meeting the purity criteria is sent to the customer. All residual materials are discarded if not meeting purity criteria. These residual materials can be sent to the customer upon request.
At your request, LifeTein can even aliquot any of your order into smaller quantities. It will be much easier for you to do the solubility test on each peptide. LifeTein's special consideration on customers' side shows our support when you need it most. The aliquots will save you time and effort in determining the solubility and save your peptides. Your peptides will have better stability because the repeated thawing/freezing, opening/closing of the container, mishandling, bacterial contamination, peptide oxidation, degradation and aggregation can be prevented.
7. What are APIs, catalog peptides and custom peptide synthesis?
APIs, active pharmaceutical ingredients, are the substances in a drug that are pharmaceutically active such as oxytocin acetate, enfuvirtide acetate and so on.
Catalog peptides are commercially available sequences. They are usually produced in bulk at high purity.
Custom peptides are usually customized according to customers' requests. For example, specific sequences, modifications, purity or length will be ordered from customers. The turnaround time for most peptides is within 2-3 weeks.
8. What is the maximum peptide length that LifeTein can produce?
LifeTein has synthesized a peptide of 120 amino acids in length. Peptides of up to 50 amino acids are routinely synthesized although in general, peptides of more than 30 amino acids can be problematic depending on the hydrophobic residues in the sequences or unusual modifications. Hydrophobicity affects the solubility of the peptide. Those difficult peptides can lead to difficulties in production.
9. What is solid phase synthesis?
Organic reactions are carried out on substrates that are covalently attached to a polymeric resin. The solid phase synthesis is better than the traditional synthesis because the overall reaction is much quicker and can be automated with robots. The synthetic intermediates do not need to be isolated. At each step, reagents are simply washed away.
10. What are resins and linkers?
Resin is the polymeric backbone that substrate is anchored to. Different resins have different swelling properties. For example, Polystyrene swells in non-polar solvents, while polyethylene glycol swells in polar and non-polar solvents. Linker is an intermediate structure between resin and substrate. Different linkers can be used to unmask different functional groups on the substrate.
11. What is a protecting group?
To ensure specific coupling between the required carboxyl and amino groups, the protecting groups should be easily and selectively attached and removed. It is a fragment that bounds to a functional group that blocks its reactivity. Some are acid labile protecting groups such as Boc and tert-Bu ester. Some are base labile protecting groups such as Fmoc and Fm ester. While some are fluoride labile protecting groups such as Tmsec and Tmse ester.
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