Capillary zone electrophoresis of alpha 1-acid glycoprotein fragments from trypsin and endoglycosidase digestions

Capillary zone electrophoresis with fused-silica tubes having hydrophilic coating on the inner walls was evaluated in the separation of peptide and glycopeptide fragments from trypsin digestion of alpha 1-acid glycoprotein. Submapping of glycosylated and nonglycosylated tryptic fragments of the glycoprotein by capillary electrophoresis was facilitated by selective isolation of the glycopeptides on concanavalin A silica-based stationary phases prior to the electrophoretic run. In addition, the electrophoretic map and submaps of the whole tryptic digest and its concanavalin A fractions, respectively, allowed the elucidation of the microheterogeneity of the glycoprotein. Also, capillary zone electrophoresis proved suitable for the mapping of the oligosaccharide chains cleaved from the glycoproteins by endoglycosidase digestion. The oligosaccharides cleaved from human and bovine alpha 1-acid glycoprotein were analyzed after derivatization with 2-aminopyridine, which allowed their sensitive detection by on column UV absorption. The separation was best achieved when 0.1 M phosphate solution, pH 5.0, containing 50 mM tetrabutylammonium bromide was used as the running electrolyte. The effect of the organic salt on separation was attributed to ion-pair formation and/or hydrophobic interaction.