The dansyl-edman method for Peptide sequencing

The dansyl-Edman method for peptide sequencing uses the Edman degradation (see Chapter 26 ) to sequentially remove amino acids from the N-terminus of a peptide. Following the cleavage step of the Edman degradation, the thiazolinone derivative is extracted with an organic solvent and discarded. This contrasts with the direct Edman degradation method ( Chapter 26 ), where the thiazolinone is collected, converted to the more stable PTH derivative, and identified. Instead, a small fraction ( approximately 5%) of the remaining peptide is taken and the newly liberated N-terminal amino acid determined in this sample by the dansyl method (see Chapter 23 ). Although the dansyl-Edman method results in successively less peptide being present at each cycle of the Edman degradation, this loss of material is more than compensated for by the fact that the dansyl method for identifying N-terminal amino acids is about one hundred times more sensitive than methods for identifying PTH amino acids. The dansyl-Edman method described here was originally introduced by Hartley (1).