[Tryptic hydrolysis extended to the level of aspartyl bonds]

A quantitative modification of free carboxyl groups in peptides and proteins can be obtained, under mild conditions, by reacting them with ethylenediamine in the presence of N-ethyl-N'-(3-dimethylaminopropyl)-Carbodimide. Aminoethylasparagine and aminoethylglutamine side chains are thus generated in place of the corresponding carboxylic ones. The first kind of residue because of its structure closer to that of lysine, is a point of greater potential trypsic cleavage than the second one. The specificity and yields of this enzymatic cleavage reaction and its possible application in sequence studies are discussed.