Analytical Sciences

Distinguishing of Linkage Isomers of Lactotetra Oligosaccharides by Using the Relative Ion Intensity Analysis of Post-source Decay Fragment Ions in Curved-field Reflectron Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry

Tohru YAMAGAKI*  and Hiroshi NAKANISHI**

*Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-0033, Japan
**National Institute of Bioscience & Human-Technology, 1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan

The native oligosaccharides of lacto-N-neotetraose (Gal beta1-4GlcNAc beta1-3Gal beta1-4Glc; LNnT) and lacto-N-tetraose (Gal beta1-3GlcNAc beta1-3Gal beta1-4Glc; LNT) were analyzed by using curved-field reflectron matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Since a curved-field reflectron TOFMS enables a simultaneous focusing of a wide mass range of metastable fragment ions, the relative ion intensities in the post-source decay (PSD) mass spectra can be discussed. The PSD mass spectra of LNnT and LNT were distinguishable in their relative ion intensities. In the case of LNT, beta-elimination could occur in the N-acetyl glucosamine (GlcNAc) at the C-3 position, which was bonded by galactose (Gal); however, it did not occur in LNnT. The 3-O elimination caused a difference in the relative ion intensities in the PSD mass spectra of LNnT and LNT. The beta1-3 glycosyl linkage cleaved more easily than the beta1-4 glycosyl linkage in the MALDI-PSD fragmentation. An analysis of the relative ion intensities in the MALDI-PSD mass spectra of oligosaccharides was very useful for distinguishing the linkage isomers and for characterizing the types of glycosyl linkages.

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