Peptide Storage Guidelines

Peptide structure and stability

Peptides are compounds formed by the dehydration condensation of α-amino acids and linked together by peptide bonds (-CO-NH-). They are intermediate products of protein hydrolysis. A compound formed by the dehydration condensation of two amino acids is called a dipeptide, and so on is tripeptide, tetrapeptide, pentapeptide, etc. Some literature refers to peptides consisting of 2 to 10 amino acids as oligopeptides or small molecule peptides; peptides consisting of 10 to 50 amino acids as peptides. Because peptides are relatively small in size, they are more susceptible to environmental factors such as temperature fluctuations and oxidation conditions, which can destroy the peptide's structure. Under normal conditions, peptide solutions can be stored for several days at room temperature, for several weeks at 4 degrees and for several months or more at -20 degrees; freeze-dried peptide powder can be stored for several months at room temperature, and stored for several years at -80 degrees.

Factors affecting peptide stability

Temperature: Increasing temperature will increase the kinetic energy of the peptide chain molecule, making its structure more susceptible to denaturation and degradation. Certain peptides depolymerize or hydrolyze at high temperatures. Although low temperatures generally help stabilize the peptide structure, extremely low temperatures may lead to the precipitation of certain solvents and excipients, which adversely affects the structural stability of the peptide.

pH: Extreme acidic or alkaline environments can lead to hydrolysis of peptides and destroy their primary structure. In addition, changes in pH can also affect the ionic strength of the peptide chain, thereby affecting the stability of its secondary and tertiary structures.

Solvent: Different solvent polarities may affect hydrogen bonds and other non-covalent interactions within and between peptide chains. Certain organic solvents may cause the structure of peptides to change. Environmental humidity and water activity can affect the hydrophobic regions of the peptide and may accelerate its degradation.

Salt concentration: High salt concentrations may affect the solubility and structural stability of the peptide, changing the folding state of the peptide by shielding charges or participating in ion exchange.

Enzymes: Proteases present in the environment may degrade peptides, rendering them inactive. Therefore, the addition of inhibitors or the maintenance of an enzyme-free environment is critical for some applications.

Light (photochemical degradation): Ultraviolet or visible light irradiation can trigger photochemical degradation of peptides, especially peptides containing tryptophan, tyrosine or phenylalanine residues that are susceptible to photooxidative damage.

Oxidation: In the presence of oxidants, easily oxidizable groups such as sulfhydryl groups in peptides may be oxidized, resulting in structural and functional changes. Similarly, a strong reducing environment can also affect the stability of some bridge bonds.

Peptide storage conditions

How to store lyophilized peptides?

Most commercially available peptides are provided in the form of freeze-dried powder and must be freeze-dried for storage. It is relatively stable at -20 ℃, and can maintain its activity for several years, especially after freeze-drying and stored in a desiccator at -80 ℃.

Before use, the original bottle containing the peptide should be placed under dry conditions (such as a drying oven filled with desiccant) and returned to room temperature. Otherwise, the stability of the peptide may be reduced due to moisture absorption. After the bottle cap is opened, it should be weighed quickly (micro-grade peptides can be dissolved in the original bottle without weighing), and sealed immediately to avoid deliquescence.

How to store peptide solutions?

The stability of the dissolved peptide will be much worse than that of the frozen dry powder. It is generally recommended that the dissolved peptide storage solution be sub-packed according to the amount of each experiment and stored at -20 ℃. Avoid repeated freezing and thawing, as repeated freezing and thawing will reduce the activity of the peptide. When using it, take the storage solution and dilute it into a working solution, which is ready for use. It is recommended to discard a small amount of peptide solution that has not been used up in the experiment that day.

Bacteria can degrade peptides, so the peptides need to be dissolved in a sterile solvent (or filtered with a 0.2/0.45 μm pore size filter to eliminate bacteria). In addition, it should be noted that peptides containing aspartic acid (Asp), cysteine (Cys), glutamic acid (Glu), methionine (Met), and tryptophan (Typ) are easily oxidized and need to be stored in an oxidant-free environment.

How to store dry peptides?

Temperature control: Most dried peptides should be stored at -20 °C or lower to slow down their degradation. Certain sensitive peptides may require lower temperatures (e.g.-80 °C).

Avoid frequent thawing: Frequent temperature fluctuations can lead to the degradation of peptides. It is recommended to dispense small portions when part of the peptide needs to be used to reduce the number of thaws.

Damp-proof measures: A desiccant pack can be placed in the storage container to avoid peptide denaturation caused by moisture absorption. Store peptides in well-sealed containers (such as screw-mouthed bottles or vacuum-packed bags) to prevent the ingress of moisture.

Storage protected from light: Many peptides are poorly stable to light and need to be placed in a container or environment protected from light.

Resolution operation: When dissolving the peptide, the recommended solvent should be used, usually sterile water or buffer, and the appropriate pH and ionic strength should be selected based on the nature of the peptide. Ensure that the peptide is completely dissolved in the solvent to avoid the formation of precipitates that affect the use effect.

Peptide storage container

Container materials used to store peptides should be chemically inert to prevent reactions with peptides, which could affect their purity and efficacy. Generally, glass or certain medical grade plastics are the preferred materials. Secondly, the container should be sealable to prevent the entry of oxygen, moisture and other pollutants and avoid peptide degradation. Temperature control is also key and needs to be suitable for storage in a low-temperature environment to extend the service life of the peptide. In some cases, it is also necessary to have protection from light to prevent the adverse effects of light on peptides. Containers should be designed with convenience in mind to ensure ease of handling and cleaning, especially in research or clinical settings where frequent access is required.

Peptide storage guidelines: General tips

Long-term storage needs to be protected from light and should be below-20 ℃, and -80 ℃ is better.

It can be stored at 4 ℃ for a short period of time. Can be transported at room temperature for a short period of time. Peptides are stable at -20 ℃ or below, especially when freeze-dried and stored in a desiccator.

Before opening the package and weighing, please balance the peptide to room temperature in a desiccator. Peptides that have not been balanced to room temperature will easily condense by water after opening the lid, which will reduce the stability of the peptide product.

Peptides containing Cys and Metor Trp are easily oxidized, and deoxygenating buffers are indispensable to dissolve them because this peptide is easily oxidized in air. Before sealing the bottle, nitrogen or argon protection will reduce the oxidation.

Peptides containing Gln or Asn are more easily degradable, and all of these peptides have a shorter shelf life than simple peptides that do not contain these problematic ones.

Peptides whose first amino acid on the N-terminal is Gln are very unstable and will degrade within a few days, so it is recommended to design the sequence without Gln appearing on the N-terminal.

The solution peptide is far less stable than the lyophilized form, and the solution should be stored at a neutral pH (pH5-7) at -20 °C.

It is best to store small samples, a sample after thawed and frozen should be thrown away decisively, bacterial degradation will sometimes become the problem of solution peptides, in order to overcome this problem peptides should be dissolved in sterile water, or the peptide solution with 0.2 μM filter membrane filtration.