Sequence Determination of a Protein with N-Terminal Glutamic Acid after Modification of Carboxyl Groups with Carbodiimide as the Coupling Agent

Abstract

Glutamine and asparagine residues in proteins can be differentiated from glutamic and aspartic residues, during the Edman degradation, after modification of the carboxyl groups by glycine methyl ester in presence of a water-soluble carbodiimide. When applied to ovine and porcine beta-lipotropic hormones, which have a glutamic acid residue at the N-terminus, the carbodiimide blocks the N-terminus. However, the Edman degradation proceeds normally, if the phenylthiocarbamyl derivative is formed prior to the modification reaction with glycine. In this communication, radioactive glycine was used to modify the carboxyl groups.