Detailed Explanation
Edman degradation was the gold standard for peptide sequencing before mass spectrometry took over. The chemistry is elegant: PITC reacts with the free N-terminal amino acid under mildly basic conditions to form a phenylthiocarbamoyl (PTC) derivative. Acid treatment then cleaves only this first residue as a thiazolinone, which is converted to a stable PTH-amino acid and identified by HPLC. The remaining peptide, now one residue shorter, is recycled for the next round. Modern automated Edman sequencers can identify 50–60 residues per run, but cumulative losses (~2–5% per cycle) limit practical sequencing to about 30–50 residues. For longer peptides, the chain is first cleaved into fragments with proteases (trypsin, chymotrypsin) and each fragment is sequenced separately.
Key Facts
- Edman degradation was the gold standard for peptide sequencing before mass spectrometry took over
- The chemistry is elegant: PITC reacts with the free N-terminal amino acid under mildly basic conditions to form a phenylthiocarbamoyl (PTC) derivative
- Acid treatment then cleaves only this first residue as a thiazolinone, which is converted to a stable PTH-amino acid and identified by HPLC
- The remaining peptide, now one residue shorter, is recycled for the next round
- Modern automated Edman sequencers can identify 50–60 residues per run, but cumulative losses (~2–5% per cycle) limit practical sequencing to about 30–50 residues
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