AAPPTec - Complete Peptide Product Source

AAPPTec provides custom peptides in the following purities:

• Immunological Grade (suitable for forming polyclonal antibodies)
• 80% or greater (tissue culture; ligand for affinity purification; non-quantitative antibody blocking experiments)
• 90% or greater (in vivo studies; bioassays; markers for electrophoresis; monoclonal antibodies)
• 95% or greater (ELISA; RIA; enzyme substrate)
• 98% (NMR; chromatography standards)

Quality control documentation provided with every peptide includes mass spectral and HPLC analyses determining composition and purity. Amino acid analysis is available upon request. We also provide storage and handling guidelines.

The HPLC-purity of most AAPPTec peptides is 95% or above. Labile peptides, e.g. peptides containing free Cys or an N-terminal Gln, or sulfated peptides, and “difficult” peptides may have lower purity.

“Research-grade” peptides are intended for laboratory and research purposes only!

They may not be used as drugs. GMP-API’s are sterile products monitored for chemical and biological contaminants applicable to humans.  All AAPPTec catalog peptides are research grade unless specifically noted otherwise.

Generally the purity of crude peptides is >60%. However, depending on the difficulty of the sequences, this estimation cannot be guaranteed for all cases.

The impurity profile and especially the peptide content can vary somewhat from batch to batch, even if the protocols of synthesis and purification have not been changed.

The impurities are mostly incorrectly synthesized peptide fragments/deletions, incompletely de-protected peptides and residual water.

The gross peptide weight is the weight determined after weighing the peptide. This is the amount indicated on the product label.

The gross weight of dry peptide doesn't 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 from the gross weight. This number may vary, from 50-90 percent, depending on the purity, sequence and method of synthesis and purification.

Peptide content is not an indication of peptide purity; these are two independent measurements. Purity is determined by HPLC and indicates the presence/absence of contaminating peptides with undesired sequences. Net peptide content only gives information on the percent of total peptide versus total non-peptide components independently of the presence of multiple peptides. 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.

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 contaminants 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.

Most peptides except those that do not have basic amino acids such as Arg, Lys, His or those with blocked N-termini exist in the form of their salts. Synthetic peptides that are purified by HPLC are usually obtained as TFA salts. Their basic amino acid residues and N-termini are protonated and have trifluoroacetate (CF3COO -) counterions.

Peptide molecules can be ionized by the Na+ or/and K+, it is common to see their adducts from the MALDI-TOF or ESI mass spectra. Those ions come from the water used for the peptide purification or the buffer used for the mass analysis. They can never be completely removed, even if distilled or deionized water is used. Instead of being ionized by a proton, some peptide molecules are ionized by Na+ or/and K+ ions. It is common and normal to observe the [M+Na] and [M+K] peaks in MALDI-TOF mass spec.

There are two common types of cyclizations that can be performed:

1. N-terminal to C-terminal cyclization

2. Disulfide bridge cyclization

N-terminal to C-terminal cyclization is confirmed by a molecular weight shift of 18 mass units in the mass spectrum. A disulfide bridge cyclization is confirmed by MS and HPLC before and after the cyclization step. Although a mass shift of 2 mass units can be difficult to detect for certain peptides, an HPLC shift helps confirm the completion of the reaction.