Custom Peptide Stability & Storage

What are the shipping conditions for the peptide I am receiving?

Most peptides are shipped at room temperature (RT), and peptides are delivered to you in a lyophilized state. These shipping conditions do not compromise quality since these products are stable at room temperatures and above for as long as several weeks. Once a product arrives at your facility, it should be kept at -20°C for long-term storage.  In a rare instance where a peptide requires shipment at low temperature, a dry ice shipment will be arranged. The cost of the shipment is the responsibility of the customer.  Light-sensitive products will be shipped with a dark bottle.  Oxidation-prone products are handled in an argon gas environment, such as those containing a Met or a free Cys, and we recommend that you do the same.

How should I store my peptide?

We recommend the following:

• Store in a desiccator or with a desiccant to maintain a dry environment.
• Store in the freezer at a temperature of -20°C
• Proper storage of a peptide can prevent bacterial degradation, secondary structure formation, oxidation, and other potential degradation for several years. Peptides are most stable in their lyophilized form at -20°C or colder in a sealed container containing desiccant.
• If peptide must be stored in solution, ensure pH is in the 3-6 range and then aliquot peptide into usable sizes to prevent damage from multiple freeze/thaw cycles. Cysteine (C), methionine (M), tryptophan (W), asparagine (N) and glutamine (Q) are most sensitive to degradation in solution.

	Duration	Storage Recommendation
Long-Term Storage	3 Months - Several Years	Lyophilized powder, frozen and desiccated, -20°C or cooler
Medium-Term Storage	0-3 Months	Frozen liquid (-20°C) or refrigerated lyophilized powder
Short-Term Storage	Less than 1 Week	Refrigerated liquid or refrigerated lyophilized powder

What is the appearance of my peptide?

The physical state for peptides ranges from amorphous solid to crystalline powder.  Some peptides will appear as a small disk at the bottom of the vial, others may appear fluffy or powdery, and other peptides may not seem visible at all.  Particularly, peptides ordered in small quantities such as 0.1 mg or 0.5 mg, may not be visible, especially through an amber glass vial.

Note: Peptides supplied as white lyophilized (freeze-dried) powder can differ in visual appearance between vialed lots due to various components in the process. For example, during exposure to nitrogen flush, the peptides can settle in different patterns. The freezing cycle can also contribute to visual differences depending on the rate; a slower rate will compact the peptide into a dense form. During the drying process, more water may evaporate, leaving the very little peptide visible to the naked eye. The pressure applied in the process will differ from lot to lot as well. These possible scenarios may change the appearance of the white mass in the vial but does not change the amount of peptide contained in the vial.

How stable is the peptide I received?

In general, peptides in solid form are quite stable.  Synthetic peptides, unlike proteins purified from cells, have an extremely low chance of proteinase contamination.

Peptides are stable for more than one year if they are stored in a lyophilized state at -20°C or below and protected from moisture and light. However, following reconstitution of a peptide in solution, stability and storage time will decrease.

If a peptide has been in solution for an extended period of time, homogeneity of the peptide must be reconfirmed.  Typically, once a peptide is in solution, it should be used within a few weeks, even when stored below -20°C.  For specific information on storage time of a peptide solution, refer to the product sheet that comes with the order.

Conditions that can affect peptide stability include the following:

• Contamination from microorganisms or metal ions can lead to peptide-bond cleavage. Use sterile buffer or water to reconstitute the peptide.
• Moisture can lead to hydrolysis of the peptide. The peptide should be allowed to warm gradually to room temperature in a desiccator to reduce condensation of water vapor.
• Constant freezing and thawing can compromise peptide integrity; therefore, stock solutions should be aliquoted.
• O₂ can negatively affect Trp, Cys, and Met residues in a peptide. If a peptide contains any of these residues, Vivitide will blanket the peptide in argon prior to sealing the vial, or screw-cap bottle.

    Certain amino acid bonds in a peptide are more problematic:

• Asp-Pro bonds are sensitive to acid cleavage.
• Asn-Gly and Asp-Gly bonds, and sometimes Asp N-term to short side-chain residues (i.e. Ser, Thr, Ala, Asn), can cyclize to form an aspartimide intermediate which, in turn, can undergo spontaneous changes that can alter the peptide.

If my peptide is hygroscopic in nature, how should it be handled?

A hygroscopic peptide contains charged amino acids (ex: Arg, Asp, Glu, His, Lys), making it vulnerable to exposure to oxygen which can lead to moisture uptake. To prevent the product from liquefying during the weighing process, it should be allowed to warm to room temperature in a desiccator prior to weighing.

If possible, weigh in a glove box to prevent exposure to oxygen and blanket vial with an inert gas prior to restorage. If this is not an option, weigh product quickly and close lid tightly to reduce exposure to the air. If you do not have ideal weighing conditions for this product, it is best to purchase smaller vial sizes to avoid storage after opening.

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, unless net peptide is requested.

How stable is a peptide?

Most peptides experience very little degradation over time and are stable for more than one year if they are stored in a lyophilized state at -20°C or below and protected from moisture and light. However, following reconstitution of a peptide in solution, stability and storage time will decrease. We do not test the stability of a peptide solution; therefore, prompt use is recommended. However, if you decide to store a peptide solution for several weeks, you should aliquot out the solution into clean, inert glass or plastic vials to prevent freeze-thaw cycles.

Conditions that can affect peptide stability include the following:

• Contamination from microorganisms or metal ions can lead to peptide-bond cleavage. Use sterile buffer or water to reconstitute the peptide.
• Moisture can lead to hydrolysis of the peptide. The peptide should be allowed to warm gradually to room temperature in a desiccator to reduce condensation of water vapor.
• Constant freezing and thawing can compromise peptide integrity; therefore, stock solutions should be aliquoted.
• Peptides containing Cys or Met are susceptible to oxidation due to the side chain groups with oxygen. It is advisable to blanket the peptide with argon or nitrogen when the vial is opened. Buffers used to dissolve these peptides should be degassed, either by bubbling argon or nitrogen through the solution for 10 minutes, or by subjecting the solution to high vacuum for 10 minutes using a common ultrafiltration capsule. Peptides containing such amino acids tend to have very short-term stability, and long-term storage is not recommended. In some cases, peptides containing Trp may be hygroscopic and require similar handling methods.

Certain amino acid bonds in a peptide are more problematic:

• Asp-Pro bonds are sensitive to acid cleavage.
• Asn-Gly and Asp-Gly bonds, and sometimes Asp N-term to short side residues (Ser, Thr, Ala, Asn), can cyclize to form an aspartimide intermediate which, in turn, can undergo spontaneous changes that can alter the peptide.

What are conditions for shipping for a custom peptide?

Most custom peptides are shipped at room temperature and delivered in a lyophilized state.  Generally, lyophilized peptides are stable at ambient temperature.  Custom peptides containing Cys or Met are susceptible to oxidation due to the side chain groups with oxygen.  These peptides are packaged under argon gas in order to displace oxygen and reduce likelihood of oxidation.  In some cases, peptides containing Trp may be hygroscopic and require packaging under argon gas as well.

What is net peptide content and what does it mean? If my peptide is 95% pure, what is in the other 5%?

The weight of dry peptide does not consist of peptide only, but includes non-peptide components such as water, absorbed solvents, counter ions and salts. Net peptide content is the actual percent weight of peptide. This number may vary, from 50 to 90 percent depending on the purity, sequence, and method of synthesis and purification. Do not confuse peptide content with purity; they are two distinctly separate things. Purity is usually determined by HPLC and defines the percent of the sample that is the target peptide sequence. Net peptide content only gives information on the percent of peptide versus non-peptide components. Net peptide content is accurately found by performing amino acid analysis or UV spectrophotometry. This information is important when calculating concentrations of peptide during sensitive experiments. If you need help, please ask us.

Peptide purity is determined by reverse-phase HPLC using a standard gradient established by Vivitide (1% per minute). During synthesis, the coupling reaction of one amino acid to another is not always 100% efficient, causing a variety of deletion sequences to be generated. Most of the deletion sequences are purified out, but a few may have similar chromatographic characteristics to the target peptide. These remain in the peptide sample and account for the percent of impurities.

See also “What is the difference between gross peptide weight and net peptide weight?”

How should a peptide be stored?

Once a product arrives at your facilities, visually inspect it and store at ≤ -20°C.  The peptide should be stored with a desiccant to maintain a dry environment.

What salt form should I use for my custom peptide?

When ordering a custom peptide or a catalog peptide, the salt form of a peptide is important. In simple in vitro experiments, a trifluoroacetate (TFA) salt is usually acceptable. However, when experiments are performed in vivo or in cell culture, one may consider ordering an Acetate (-OAc) or hydrochloride (HCl) counter ion to minimize any issues associated with TFA. There is usually a small charge for exchange of the counter ion, but this is worth it to eliminate some of the associated issues known for TFA especially in cell culture experiments and animal models.

Liability Disclaimer

All products sold by Vivitide are intended solely for laboratory and research use and should not be used in or on human subjects.  User assumes all risk of patent infringement by reason of use of material provided by Vivitide. Vivitide will not be responsible for damages arising from misuse of any product and is not responsible for the results of research using our products.