CHARACTERIZATION OF OLIGOSACCHARIDE COMPOSITION AND STRUCTURE BY QUADRUPOLE ION-TRAP MASS-SPECTROMETRY

The use of electrospray ionization-quadrupole ion trap mass spectromet ry for the characterization of linear oligosaccharides and N-linked pr otein oligosaccharide mixtures is described. Tandem mass spectrometry (MS/MS) experiments with orders higher than two offer a number of ways to enhance MS/MS spectra and to derive information not present in MS and MS2 spectra, Three such methods are presented in this paper. (a) C ollisional activation of permethylated oligosaccharide molecular ions (MS2), as illustrated by maltoheptaose, produces abundant fragments fr om glycosidic bond cleavages which indicate composition and sequence, and weak cross-ring cleavage products which denote specific linkages w ithin the oligosaccharide. Through the trapping and further dissociati on of these fragments (MSn), cross-sing cleavage products can be confi rmed and their relative abundances increased to facilitate interpretat ion. (b) The mechanisms of formation of two isobaric ions or ions isob aric with another ion's isotope peaks, such as those present in the MS 2 spectrum of the ribonuclease B oligosaccharide GlcNAc(2)Man(5) can b e independently established by separate MS3 experiments. (c) Ions in t he MS2 spectrum, specific for individual components of an isobaric mix ture, can be isolated and characterized by further stages of fragmenta tion. This is illustrated by two isobaric oligosaccharides from chicke n ovalbumin of the composition HexNAc(5)Hex(5). These findings indicat e the utility of ion trap mass spectrometry towards the facile determi nation of oligosaccharide composition, sequence, branching and linkage , providing a wealth of structural information not obtainable by other individual methods of carbohydrate mass spectrometric analysis. (C) 1 997 by John Whey & Sons, Ltd.