Dansyl Chloride
 
 The repetitive nature of the Edman Degradation reaction opened the way to protein sequencing and to automation in the form of protein sequencers, but manual Edman degradations also became popular during much of the 1960s and 1970s.
One major manual method used dansyl (1-dimethylaminonaphthalene-5-sulphonyl) chloride (Fig. 1) to detect the new N-terminus after each Edman cycle (1). Combined with purification of peptides on paper by high-voltage electrophoresis and chromatography, it made protein sequence analysis accessible to many laboratories without the need for large equipment. It also avoided the difficulties in identification of the phenylthiohydantoin (PTH)-amino acids that existed early, and replaced PTH-identification with dansyl-amino acid identification. The latter became rapid and reliable by thin-layer chromatography (2). Hence, many of the original protein primary structures determined used this methodology, originating from the MRC Laboratory of Molecular Biology, Cambridge, England. Together with the Sanger method of DNA sequencing later developed there, the “dansyl-Edman/paper purification” technique made this laboratory the leader in sequencing technology for a long time in the 1960s and 1970s.

Figure 1. Principle of the “dansyl-Edman” modification of the Edman degradation reaction, with N-terminal analysis of separate samples. PITC, phenylisothiocyanate; ATZ, anilinothiazolinone; PTH, phenylthiohydantoin; Dansyl, 1-dimethylaminonaphthalene-5-sulphonyl.
Dansyl chloride reacts with protein N-termini much like the original Sanger reagent, fluorodinitrobenzene (FDNB) (3), but it is easier to use, more sensitive, and fluorescent, making it easily detectable. Dansyl chloride is still used for protein labeling in many cases where fluorescence is desirable.
References
1. W. R. Gray (1967) Methods Enzymol. 11, 469–475 and (1972) 25, 121–138.
2. K. R. Woods and K.-T. Wang (1967) Biochim. Biophys. Acta 133, 369–370.
3. F. Sanger (1945) Biochem. J. 39, 507–515.