Analysis of isomeric glutamyl peptides by capillary electrophoresis. Application to stability studies

Capillary electrophoresis has been used for the separation of the glutamyl tripeptides Gly-alpha-Glu-Phe-NH2 and Phe-alpha-Glu-Gly-NH2 including their potential degradation and isomerization products Gly-gamma-Glu-Phe-NH2, alpha-Glu-Phe-NH2, gamma-Glu-Phe-NH2 and Phe-NH2 as well as Phe-gamma-Glu-Gly-NH2, Phe-Glu and Phe, respectively. Between pH 2.2 and pH 10.0 the effective mobilities of the glutamyl peptides have been investigated. Using histidine hydrochloride as internal standard at pH 2.2 linear calibration curves for both assays were obtained for a concentration range from 10 microg ml(-1) to 3.5 mg ml(-1). The assay was applied to analyze the degradation of the tripeptides in solution at pH 7 and pH 3 at 70 degrees C. Hydrolysis and isomerization of the glutamyl peptides were found in the incubation mixtures.