Microsequencing of Peptides and Proteins with 4-N,N-Dimethylaminoazobenzene-4'-isothiocyanate

Manual methods for the stepwise N-terminal degradation of polypeptides have been widely applied in protein chemistry. The technique most commonly used up to now, has been the Edman degradation, carried out either manually (1) or automatically (2-4). Although nowadays the reaction can be performed with high efficiency and automatically in a sequencer, the manual methods are still of value. The reasons for this are: (i) The manual methods can be easily applied in any laboratory, even by an inexperienced researcher, with a minimum of equipment at low cost; (ii) It is possible to simultaneously screen many pep-tides for purity, and to gain information in a reasonable time about the N-terminal sequences of sets of peptides generated by proteolytic or chemical cleavage; (iii) The selection of fragments of high purity for the sequencer or those peptides that need to be sequenced in a machine because of length, hydrophobicity, or difficult sequence stretches is made easier.