Abstract
Reductive amination with n-hexylamine followed by permethylation was used as a procedure for the liquid secondary ion mass spectrometry (LSIMS) analysis of Asn-linked oligosaccharides. Initial experiments with this procedure were performed on maltoheptaose. These experiments show that exhaustive methylation at the newly formed secondary nitrogen forms a quaternary ammonium salt. When this is subjected to positive ion LSIMS, an abundant M + ion is observed. This procedure was applied to the Asn-linked oligosaccharides released from human transferrin and ribonuclease-B. The reductively aminated, permethylated mixture of oligosaccharides from ribonuclease-B afforded a positive ion LSI mass spectrum in which M + ions for Man 5–9GlcNAc 2 could be assigned. The positive ion LSI mass spectrum obtained from the mixture of oligosaccharides isolated from human transferrin showed M + ions that could be assigned to both monosialylated and disialylated biantennary complex type oligosaccharides. Reductive amination followed by permethylation of the Asn-linked oligosaccharides isolated from baculovirus expressed mouse interleukin-3 produced in Bombyx mori gave a positive ion LSI mass spectrum in which the oligosaccharides could be assigned the monosaccharide composition Man 2–4[Fuc]GlcNAc 2 and Man 2GlcNAc 2. These are believed to be dimannose, trimannose, and tetramannose chitobiose core oligosaccharides, three of which are fucosylated.
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