Edman degradation and peptide sequencing.
A peptide's mass says it is probably the right molecule; reading its sequence confirms it. Edman degradation reads a peptide one residue at a time from the N-terminus, peptide mapping fingerprints larger molecules, and tandem mass spectrometry now does most sequencing. Here is how each works.
One residue per cycle.
Pehr Edman described the method in 1949 and automated it in a protein sequenator in 1967. Each cycle has three steps. Phenyl isothiocyanate (PITC) reacts with the free amino group of the N-terminal residue; acid, usually trifluoroacetic acid, cleaves that labeled residue off as an anilinothiazolinone; and it is converted to a stable phenylthiohydantoin (PTH) amino acid that chromatography identifies. The rest of the chain, now one residue shorter, goes into the next cycle.
Length, amount and blocked ends.
Each cycle is slightly incomplete, so background builds up and limits how far a run can go. A 1981 instrument gave useful data from about 5 picomoles and runs of more than 30 residues on subnanomole amounts. Edman also needs a free N-terminal amino group: an acetylated or pyroglutamate N-terminus blocks it until the cap is removed. That matters for capped peptides such as TB-500 and thymosin alpha 1, both acetylated, and ARA-290, which starts with pyroglutamate. N-terminus vs C-terminus explains the caps.
A fingerprint for larger molecules.
For proteins and large peptides, a peptide map cuts the molecule into fragments with an enzyme such as trypsin or a chemical, separates them by HPLC and identifies them, then compares the pattern with a reference. Mapped by LC-MS/MS, it confirms identity residue by residue across the whole molecule, and it is standard for biologic drugs.
Sequencing by fragments.
Tandem mass spectrometry (MS/MS), shown for protein sequencing in 1986, breaks a peptide into fragments inside the instrument and reads the sequence from the mass differences between them. It works with blocked N-termini and small amounts, and it is now the main way peptides are sequenced. For a short synthetic peptide, the intact mass from MS plus HPLC purity is the usual identity and purity check.
Identity by mass.
Helion's lab reports confirm identity by mass spectrometry and measure purity by HPLC. How peptides are tested walks through each result, and how to verify a COA explains checking a report with the lab that issued it.
Specs and storage by compound.
Questions (6)
What is Edman degradation?
A method that reads a peptide's sequence one residue at a time from the N-terminus, by labeling, cleaving and identifying each terminal amino acid in turn.
What reagent is used in Edman degradation?
Phenyl isothiocyanate (PITC), which reacts with the N-terminal amino group.
Why can't Edman degradation sequence acetylated peptides?
It needs a free N-terminal amino group. An acetyl or pyroglutamate cap blocks the first step until it is removed.
How many residues can Edman degradation read?
Runs of more than 30 residues were reported on small amounts with automated sequencers; background from incomplete cycles limits longer runs.
What is peptide mapping?
Cutting a protein or large peptide into fragments, separating them by HPLC and identifying them, then comparing the pattern with a reference.
How are peptides sequenced today?
Mostly by tandem mass spectrometry, which reads the sequence from the masses of fragments.
Published studies (8)
- A method for the determination of amino acid sequence in peptides
- A protein sequenator
- A gas-liquid solid phase peptide and protein sequenator
- Availability of phenylisothiocyanate for the amino acid sequence/configuration determination of peptides containing D/L-amino acids
- Sequencing of peptides and proteins with blocked N-terminal amino acids: N-acetylserine or N-acetylthreonine
- High-yield deblocking of amino termini of recombinant immunoglobulins with pyroglutamate aminopeptidase
- Development of an LC-MS/MS peptide mapping protocol for the NISTmAb
- Protein sequencing by tandem mass spectrometry
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.