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The impurities in non-purified peptides are both peptides and non-peptides, the impurities in purified peptides are mostly peptides with modified sequences, except for TFA salt. The net peptide content is different from the peptide purity. The net peptide content is the percentage of peptides relative to nonpeptidic materials, mostly counterions and moisture. The net peptide content can be determined by amino acid analysis. Please place a request for a quote if you require this service.

Usually, hydrophilic peptides absorb tiny amounts of moisture even under strict lyophilization conditions. Net peptide content may vary from batch to batch depending on the purification and lyophilization processes. Peptides are usually delivered as TFA salts. If residual TFA would be problematic for your experiment, we recommend other salt forms such as acetate and hydrochloride. The synthetic peptides are manufactured by solid-phase procedures. TFA is usually used for cleavage and purification steps. TFA binds to the free amino termini and side chains of positively charged amino acids.

Unlike the natural protein synthesis, peptides are synthesized from the C to N-terminus. 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. This reveals a new N-terminal amine to which the next amino acid may be activated by one of the several reagents, forming a peptide bond. When the synthesis is complete, peptides are cleaved from the resin and deprotected. Peptides are then precipitated, washed, and lyophilized.

All materials supplied to LifeTein are considered the confidential property of the customer. Peptides are purified by reverse-phase chromatography. The chromatogram indicates the number and relative amount of by-products.

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The molecular mass of the peptide is determined by mass spectrometry to confirm that the correct product is being delivered. MS results also show the masses of the main impurities. Additional analysis revealing net peptide content can be performed upon request. Net peptide content is indicated by either amino acid analysis or elemental analysis. These methods allow the verification of the amino acid composition of the peptides. They serve as additional means of confirmation of peptide identity.

All synthetic peptides meeting the customer's purity criteria are sent. All residual materials, such as peptides not meeting the customer's purity criteria are discarded.

Peptide Synthesis in the Laboratory

These residual materials can be sent to the customer upon request. Aliquoted products are more expensive but may save you time, effort and money during the determination of peptide solubility. Your peptides will also be more stable because they will not be exposed to as many freeze-thaw cycles, as many openings and closings of the container, mishandling, or bacterial contamination. Peptide oxidation, degradation, and aggregation are less prevalent in aliquoted samples.

APIs active pharmaceutical ingredients are the substances in drugs 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 levels of purity. These peptides are usually customized to customers' specific requests.

For example, specific sequences, modifications, purity levels, or lengths may be required by the customer.


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The turnaround time for most API peptides is weeks. The minimumal quantity to be ordered should be at leastis 1 mg. Peptides of 50 amino acids are synthesized routinely. Organic reactions are carried out on substrates covalently attached to a polymeric resin. Solid-phase synthesis can be better than the traditional synthesis because the overall reaction takes place much more quickly, the process can be automated with robots, and synthetic intermediates do not need to be isolated because reagents are washed away during each step.

Resin is the polymeric backbone to which substrates are anchored. Different resins have different properties. For example, polystyrene swells in non-polar solvents, while polyethylene glycol swells in polar and non-polar solvents. Linkers are intermediate structures that attack the resin to the substrate. Different linkers can be used to unmask different functional groups on the substrate.

Protecting groups are fragments that binds to functional groups and blocks their reactivity. Some are acid-labile protecting groups such as Boc and tert-Bu ester.

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Professor Katrina Jolliffe - The University of Sydney

Some are base labile protecting groups such as Fmoc and Fm ester. Some others are fluoride-labile protecting groups such as Tmsec and Tmse ester. To ensure specific coupling between the required carboxyl and amino groups, the protecting groups should be easy to attach and remove without changing the rest of the peptide. Chemically synthesized peptides carry free amino and carboxy termini.

The need for N-terminal acetylation or C-terminal amidation must be stated explicitly during ordering. It is impossible to perform these modifications after synthesis has been completed.

Professor Katrina Jolliffe

N-terminal acetylation and C-terminal amidation reduce the overall charge of a peptide and decrease solubility. However, the stability of the peptide usually increases because the terminal acetylation and amidation allow the peptide to mimic the native protein more closely. In this way, these modifications may increase the peptide's biological activity. We recommend N-terminus modification for its higher success rate, shorter turnaround time, and ease of operation.

Peptides are synthesized from the C-terminus to the N-terminus.


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  • N-terminus modification is the last step in the SPPS protocol. No more specific coupling steps are required. In contrast, the C-terminus modification requires additional steps and is usually more complex.

    Protection of Functional Groups in Peptide Synthesis

    Most dyes are large aromatic molecules. The incorporation of such bulky molecules may help to avoid interactions between the label and the peptide. This will help maintain peptide conformation and biological activity. It is recommended that a flexible spacer such as Ahx a 6 carbon linker be included to render the fluorescent label more stable. Otherwise, FITC could easily link to a cysteine thiol moiety or the amino group of lysine at any position. Peptide purity is the term used to describe the percentage of peptide with the target sequence among the total quantity of material.

    For example, some chains might not be complete, or amino acids might not bind appropriately. These deleted or incorrect sequences form a certain percentage of peptides in most peptide mixtures. We analyze and purify crude peptides using reverse phase HPLC, and then analyze the resulting material using MS to achieve the desired target sequence purity. After your peptide has been purified and lyophilized, the white peptide powder will contain some non-peptide components such as water, salts, absorbed solvents, and counter ions. The peptide content describes the actual percentage weight of the peptide in your final product.

    When calculating the concentration of peptide solutions for biological assays or other experiments, it is essential that the peptide content is accounted for. The actual peptide concentration can be determined by subtracting the non-peptide weight from the total weight, which allows you to determine what volume of solvent to use. It is important to note that peptide content and peptide purity are two distinct measurements. Purity is determined using HPLC, and revealed the presence or absence of contaminating peptides with the incorrect sequences.


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    • In contrast, the net peptide content provides only information regarding the percent of total peptide vs. The net peptide content can be determined accurately by performing amino acid analysis or UV spectrophotometry. It is difficult to determine the actual concentration of a peptide based on the weight of the lyophilized peptide. Generally, hydrophobic peptides contain less bound water and salts than do hydrophilic peptides.

      If the peptide has a chromophore in its sequence W or Y , the peptide concentration can be determined conveniently using the extinction coefficient of these residues as follows:.