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Asparagine-linked glycans of bovine fetuin were separated by capillary gel electrophoresis after enzymatic release (peptide-N-glycosidase F) and labeling via reductive amination by a fluorescent dye, 1-aminopyrene-3,6-8-trisulfonate (APTS). At low separation pH (2.5) only two dominant peaks were observed. Increasing the separation buffer pH to 4.75 resulted in complete separation of two primary doublets and several minor peaks from the fetuin N-linked glycan pool. Two of the four major peaks were spiked with purified individual standards and were identified as trisialylated triantennary structures with different sialylation linkages. The other two larger peaks were postulated to be tetrasialylated triantennary structures, based on calculations considering their corresponding glucose unit (GU) values. Effects of the electrophoretic separation parameters, such as gel concentration, electric field strength and temperature on the migration behavior of the two major doublets of the fetuin glycan pool were also thoroughly examined. Our data suggest that the capillary gel electrophoresis separation of the multisialylated branched oligosaccharides with different linkage isomers, released from bovine fetuin, is fundamentally based on their degree of sialylation and hydrodynamic volumes.

The reductive amination of monosaccharides with 8-aminopyrene-1,3,6-trisulfonate (APTS) in seven different organic acids including the commonly used acetic acid was investigated by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. The correlation between the yields of the saccharide-APTS adducts and pKa of the organic acid catalyst is consistent with general acid catalysis of the rate-determining step of the reductive amination reaction. Derivatization in the presence of organic acids of higher strength than acetic acid produced substantially higher yields of APTS-sugar adducts, an effect which is more pronounced for N-acetylamino sugars. Optimum yields were obtained using citric acid as a catalyst. Conversion of a few nanomoles of neutral saccharides to the APTS derivatives is achieved at 75 degrees C in less than 60 min.

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