Abstract
In order to establish a simple and rapid method for the differentiation of α- and γ-glutamyl linkages, mass spectra of a series of α- and γ-glutamyl oligopeptides including di-, tri-, and tetrapeptides were examined and the following results were obtained. 1) Generally the spectra of the α- and γ-isomers were distinguishable in several fragment peaks ; particularly, ions c and h arising from the cleavage of glutamyl Cα-CO bond (Chart 2) are characteristic to the α-isomers, while ions e and g due to the ring formation of glutamyl chain (Chart 3) appeared intensely in the γ-isomers. The peak intensity ratios of these ions, c/g and h/e, which were large for the α- and small for the γ-isomers, were especially useful for the assignment of the glutamyl linkages. 2) As a result the whole structures of the α- and γ-glutamyl peptides (up to around tetrapeptide) were easily determined from the mass spectra of their Z or Dec derivatives. 3) All of the four structural isomers of glutamyllysine were easily distinguished from their mass spectra. 4) The method presented here was successfully applied to determine the full structures of some natural glutamyl peptides such as glutathione and cross-linking peptides found in certain peptidoglycans and proteins.
