Carboxyl group modification and amide assignments in automated sequencing of proteins

Abstract

A procedure is described for locating the amidated and non-amidated residues in automated sequence analysis of proteins. The method requires no additional identification procedure beyond hydrolysis of the thiazolinone derivatives followed by amino acid analysis. The free carboxyl groups of ribonuclease A were coupled with serine methyl ester or glycine ethyl ester in the presence of a water soluble carbodiimide. The derivatized proteins were then subjected to automated Edman degradation in the protein sequenator. At positions where the residue in the native protein was aspartic or glutamic acid, the coupled amino acid was recovered in addition to aspartic acid or glutamic acid after hydrolysis of the thiazolinone derivatives.