Liquid secondary ion mass spectrometry analysis of permethylated,n-hexylamine derivatized oligosaccharides. Application to baculovirus expressed mouse interleukin-3

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 Mans_5–9GlcNAc₂ 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_2–4Fuc]GlcNAc₂ and Man₂GlcNAc₂. These are believed to be dimannose, trimannose, and tetramannose chitobiose core oligosaccharides, three of which are fucosylated.