The solubility of peptides is sequence dependent. Many peptides will solubilize readily in water or phosphate buffered saline with gentle sonication. If the peptide will not dissolve readily varying the pH can help. If the peptide is acidic, try raising the pH slightly. If it is basic, try lowering the pH.

For more hyrophobic sequences, some organic may be necessary to dissolve the peptide. Dimethylformamide(DMF) or Dimethylsulfoxide(DMSO) can be added if it is compatible with your protocols. 1% Sodium dodecyl sulfate, or 8M Urea can also be tried for difficult solubilzations.

Some important things to remember:

1. GPS will contact the customer if there is an extremely hydrophobic sequence that could be problematic during solubilization. Recommended solubilization suggestions will be listed on the Certificate of Analysis, but please don’t hesitate to contact our technical services if questions persist.
2. If it is necessary to add organic to the sequence, add the organic BEFORE adding the aqueous solvent. Organic solvent is generally added to peptides containing hydrophobic amino acids: Val, Ala, Leu, Iln, Phe.
3. A rule of thumb in determining peptide pH is the following: Arg, Lys, His and N-terminal -NH2 all contribute to the basic pH of a peptide. Asp, Glu and C-terminal COOH contribute to the peptide’s acidity. Assigning +1 values to basic residues (including CONH2) and -1 values to acidic residues (including CCOOH) within the peptide will yield an overall acidic/basic rating.
4. If the peptide is basic and does not dissolve in water, try adding 10% acetic acid dropwise with vortexing in between. Only use diluted trifluoroacetic acid when acetic acid has failed, as it can be damaging to cells. For acidic peptides try using 10% ammonium hydroxide.

Ideally, peptide sequences should be 10-30 residues in length, be relatively hydrophilic and possess few or none of the avoidances discussed in Question 2. It must be remembered that in addition to avoiding difficult sequence compositions, long sequences contribute to a peptide’s difficulty and achieved purity.

Peptides, unlike oligonucleotides, which can be produced quickly and predictably, are often difficult to synthesize due to their many chemically different residues. Modern Fmoc synthesis chemistry and improvements in automated instrumentation have greatly improved the efficiency, cost and quality of resulting peptides, but expert chemists are still required for adequate problem solving, synthesis and purification method determination.

Yes. Utilizing state-of-the-art bioinformatics software and years of expert peptide chemistry experience, we’ll be glad to assist you.

For maximum stability GPS recommends that peptides be stored lyopholized at -20C. If a peptide is to be stored in solution it is recommended that individual aliquots are frozen to to avoid numerous freeze/thaw cycles that can degrade the peptide.

Synthetic peptides have been successfully produced that exceed 100 amino acid residues. The success of such syntheses however, are entirely sequence dependant and purity would likely be very low. Realistically, going above 40 amino acids in length is often “experimental” territory and will significantly affect cost. GPS regularly produces peptides in excess of 40 amino acids.

Some deletion sequences that result from incomplete coupling may have similar retention properties to the full-length sequence during RP-HPLC purification. Although the majority of deletion-mers are removed, the remaining few contribute to the overall net peptide impurities.

It is important to understand the distinction between net peptide content and total peptide content. Net peptide content is percentage of actual peptide material minus any counter ions, salts, absorbed water or solvents and is usually what is meant when one thinks of “peptide purity.” The total peptide content is the peptide, plus all of the residual components just mentioned that are virtually impossible to completely remove from the dry, purified peptide. It is this material that is referred to in the stated weight of your delivered peptide. Net peptide composes approximately 80% of the total weight and can be accurately determined through Amino Acid Analysis, which is available at cost upon request.

To say it another way, RP-HPLC purifies the peptide to yield what is considered the net peptide purity (a percentage ONLY taking into account the amount of full-length vs. non-full-length peptide present). Once the peptide has been lyophilized, the peptide that has a net peptide purity of >95% may reveal through Amino Acid Analysis that the total peptide content is 80%. That means that by weight 80% is pure, full-length peptide and 20% is absorbed solvent and water, counter-ions, and salts.

When a customer requests a peptide of >95% purity, only <5% of the peptide is not the full sequence, but the delivered peptide is not 95% peptide by weight. For most applications one doesn’t need to perform Amino Acid Analysis to determine net peptide content for the exact ratio of peptide to non-peptide material for quantification in experimental use.

GPS uses solid phase chemistry utilizing the Fmoc/tBu protection scheme.

Each custom peptide is supplied with Mass Spectrometry spectrum and Analytical HPLC trace. In addition, a Certificate of Analysis is included which states the essential peptide information and suggested solubility conditions. Each peptide is guaranteed to meet the requirements of the order at the time of delivery or GPS will re-synthesize or re-purify the peptide in question, or refund your money.

GPS can conjugate using a variety of linker and side chains of amino acids. We recommend attachment through a free sulfhydryl on a Cysteine residue for conjugation. However, if other methods are required, attachment can be directed through a hydroxyl on Ser, Thr; carboxyl, as in Glu, Asp and C-terminus; or via a primary amine (Lys or N-terminus).

Peptides are supplied as a lypholized powder, with a triflouoroacetate counter ion. Other counter ions are available upon request.

These terminal modifications mimic charges found in some hydrophobic, internally isolated protein sequences, or inter-membrane proteins of a native environment.

LC (long chain) biotin is a biotin molecule spaced away from the peptide with the six carbon spacer -amino-hexanoic acid.

Most of our cyclized peptides are oxidized while the Trp is still protected which insures the Trp remains in its reduced form. The peptide is purified after the cyclization, which eliminates any oxidized Trp. Oxidation of any of the peptide residues can be seen as a mass gain of 16 Amu.

If Cysteines are present store peptides dry. When solubilized use dilute concentration and keep acidified. Addition of a reducing agent such as betamercaptoethanol or dithiothreitol is advisable, if possible.

Cyclization is confirmed by a mass loss of 2 Amu in MALDI-MS and a shift seen in HPLC elution time. Ellman’s test is also used to verify the absence of free thiols when applicable.

AAALAC - accredited, USDA Research Licensed, OPRR assured and managed under Good Manufacturing Practices. All protocols are IACUC reviewed.

GPS recommends using >85% peptide purity for polyclonal antibody production. Although using a lower purity peptide will not affect antibody response, subsequent screening and purification results will be improved with higher purity peptides. For Monoclonal Antibody production, >95% purity is recommended.

GPS uses a platform of parasites, protozoa, viruses, and bacteria to screen for to ensure that the most common illnesses found in conventional colonies, including pasteurella and bordetella, are not present in our colonies. If you’d like a complete listing of what we screen for to maintain our specific pathogen free status, please let us know.