Practical Protein Chemistry - A. Darbre 1989

Determination of the amino acid sequence of peptides by the Edman degradation method with identification of dansyl amino acids
Introduction

G. WINTER (MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB'2 2QH, U.K.)

Dansyl chloride (1-dimethylamino-5-naphthalenesulfonyl chloride) reacts with the α-amino group of a peptide (as well as with the side-chain groups of Cysteine, Tyrosine, Lysine, and Histidine residues) to yield a dansylated peptide derivative (DNS-peptide). Upon acid Hydrolysis of the peptide thus modified, its N-terminal residue is cleaved off as a fluorescent dansyl amino acid, which can be readily identified by Chromatography on polyamide thin-layer plates [5]. Under these hydrolysis conditions, dansyl derivatives of Tryptophan and dicarboxylic amino acid amides are completely destroyed, while dansyl-Proline and dansyl-Serine are partially degraded; among the side-chain derivatives, only ε-dansyl-lysine and O-dansyl-tyrosine remain intact.

When determining the Amino Acid Sequence using the dansyl method [6, 7], after each cycle of Edman Degradation, the N-terminal residue of the shortened peptide is analyzed by dansylating a small aliquot of the sample. This technique compares favorably with the classical Edman method and its DABITC-PITC modification [1] by eliminating The Need for washing phenylthiocarbamyl Peptides after the coupling stage, thereby preventing potential losses of peptides (especially non-polar ones) due to dissolution in the organic phase. The gradual decrease in The amount of material available for analysis (resulting from sampling for Dansylation) is compensated for by the much higher sensitivity in detecting fluorescent Amino Acid Derivatives.