Peptide Synthesis

We had produced the peptides containing 200 residues. However, peptides longer than 100a.a are extremely difficult to synthesize. We can evalute them case by case and try our best to make them by fragmentation and ligation.

We had produced peptides containing 16 consecutive Pro residues. If you'd like to, we can have a try, but it is hard to ensure success.

For the sequence with "Q" at the N terminus, it is important to note that this configuration is not stable and may undergo a cyclization reaction to form pGlu. While obtaining a qualified peptide with this sequence can be challenging, we are willing to make an attempt if you are interested. However, if the peptide is urgently needed for your project, you may consider the following options to prevent such cyclization:
Removing "Q" from the N-terminus
Adding another amino acid in front of "Q"
Applying N-terminus acetylation.

In chemical terms, a counterion is an ion of opposite charge to another ion in a solution or an electrochemical system. In peptide synthesis, counterions such as TFA are used for cleavege and HPLC separation, and TFA counterions binds to the basic amino acids or N-termini, so synthetic peptides are usually obtained as TFA salts. In some cases, TFA counterions may be harmful to biological assays (see Top 5 reasons peptide assays fail), however GenScript can replace TFA counterions with acetate or HCl, upon requesting our TFA removal service.

It is important to understand the difference between net peptide content and total peptide content. The dry peptide powder shipped to you usually contains not only peptides, but also some other substances such as water, absorbed solvents, counterions, and salts. The total peptide content(gross weight) refers to the weight of this mixture. Net peptide weight indicates the actual weight of the peptide component of your sample. Net peptide content is usually 50-80% of the total peptide weight (also called gross peptide weight) and is usually determined by amino acid analysis or Nitrogen analysis. Net peptide content should not be confused with purity. Purity defines the percentage of the target peptide sequence in the peptide component of your sample.

Theoretical net peptide content (calculated assuming that counterions are the only non-peptide components present in your peptide sample) can be estimated by dividing molecular weight of the peptide by a sum of this molecular weight and a number of trifluoroacetate counterions that are required to neutralize the peptide multiplied by the molecular weight of the TFA counterion (MW= 114). For example, a synthetic peptide of MW=1000 with a free N-terminal amino group and one Arg has theoretical net peptide content of 1000/(1000 + 2 x 114 ) = 1000/1228 =0.81 or 81%. In practice, counterions are not the only possible non-peptide impuritiies in the peptide sample. It can also contain water, absorbed solvents and traces of other substances. As a result, the actual net peptide content is usually determined by quantitative amino acid analysis.

Highly hydrophobic peptides are prone to aggregate, which increases the difficulty of synthesis. Highly hydrophobic peptides are easy to adhere to the column, which increases the difficulty of purification.

For the purity that is less than 70%, GenScript would set it as crude.

An appropriate peptide purity is a critical factor for the success of a scientific experiment. In general, the higher the peptide purity level, the more favorable the experimental outcome. Impurities in lower purity peptides may result in toxicity or unwanted side reactions, especially for some applications such as animal studies where exceedingly pure peptides (>98% purity) are required. More details can be found at this link: https://www.genscript.com/peptide-purity.html

In general, GenScript will lyophilize the target fraction in purification directly, the main reagents are the ultrapure water, acetonitrile and TFA in mobile phases.

Peptides are delivered in lyophilized powder form by default, aliquoted in individual sample tubes. Meanwhile, peptides can be delivered according to customer’s requirements.

A regular peptide label contains peptide name, peptide service type, quantity, purity and Lot number. If extra information is needed, such as sequence or molecular weight, please kindly add this request when making the quote, GenScript can provide a customized label.

In general, the appearance of a peptide is closely related to the peptide sequence itself, it is not recommended to do comparison between different peptides. Besides, peptides delivered as white lyophilized (freeze-dried) powder can differ in visual appearance between peptides due to the retention of different compositions in the final sample. For example, the freezing cycle can 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 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 peptide sample in the vial but do not change the amount of peptide contained in the vial, which is weighed via analytical balance.

The delivered peptides are accurately weighed and aliquoted, if the peptides are invisible, there are several reasons for your reference:

1. The peptide amount is too small to be visible using naked eye. It is recommended to dissolve the peptide in the vials provided by GenScript, then perform the experiments directly.

2. Peptides might be adhered to the vial wall or cap, it is recommended to perform centrifugal or shake operation before your experiments.

3. Hydrophilic sequences absorbed water during the transit or storage, it is recommended to re-lyophilize the peptides before experiments.

There are three common shipment temperatures: room temperature, blue ice (approximately 4 degrees) and dry ice (approximately -80 degrees).

Without specific requests, peptides in lyophilized powder format will be sent out at room temperature, and peptides in liquid format will be sent out with dry ice.

If there are special requests, please kindly add the note when preparing the quote or let GenScript know.

Adding PEG or several Lys (3~4) in the sequence may improve the hydrophilicity of the peptides.