In 1950, Edman published a chemical method for the stepwise removal of amino acids from the N-terminus of a peptide (1 ). This series of reactions has come to be known as the Edman degradation, and although modifications of this technique have been introduced from time to time, the Edman degradation method remains, over thirty years after its introduction, the only effective chemical means of removing amino acids in a stepwise fashion from a polypeptide chain. The overall reaction sequence is shown in Fig. 1 . The reactions may be conveniently divided into two stages:
