THE IDENTIFICATION OF ABNORMAL GLYCOFORMS OF SERUM TRANSFERRIN IN CARBOHYDRATE-DEFICIENT GLYCOPROTEIN SYNDROME TYPE-I BY CAPILLARY ZONE ELECTROPHORESIS

One of the biochemical characteristics of carbohydrate deficient glyco protein syndromes is the presence of abnormal glycoforms in serum tran sferrin. Both glycoform heterogeneity and variable site occupancy may, in principle, lead to the generation of a range of glycoforms which c ontain different numbers of sialic acid residues, and therefore variab le amounts of negative charge. Capillary zone electrophoresis was used to resolve the glycoforms of normal human serum transferrin and also of a set of glycoforms which were prepared by digesting the sugars on the intact glycoprotein with sialidase. The sugars on the intact glyco protein were also modified by a series of exoglycosidase enzymes to pr oduce a series of neutral glycoforms which were also analysed by capil lary zone electrophoresis. The oligosaccharide population of human ser um transferrin was analysed by a series of mixed exoglycosidase digest s on the released glycan pool and quantified using a novel HPLC strate gy. Transferrin was isolated from carbohydrate deficient glycoprotein syndromes type I serum and both the intact glycoforms and released sug ars were resolved and quantified. The data presented here confirm the presence of a hexa-, penta- and tetra-sialoforms of human serum transf errin in both normal and carbohydrate deficient glycoprotein syndrome type I serum samples. Consistent with previous reports carbohydrate de ficient glycoprotein syndrome type I transferrin also contained a di-s ialoform, representing a glycoform in which one of the two N-glycosyla tion sites is unoccupied, and a non-glycosylated form where both remai n unoccupied. This study demonstrates that capillary zone electrophore sis can be used to reserve quantitatively both sialylated and neutral complex type glycoforms, suggesting a rapid diagnostic test for the ca rbohydrate deficient glycoprotein syndromes group of diseases.