期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1981
卷号：78
期号：3
页码：1471-1475
DOI：10.1073/pnas.78.3.1471
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Field desorption mass spectrometry has been used to analyze carbohydrate polymers with 5 to 14 hexose units without prior derivatization. In all examples, the molecular weight of the oligosaccharide could be determined by means of the abundant quasimolecular ions of the type MNa+, MH+, MNa22+, and MNa33+. Fragmentation at glycosidic linkages was observed in varying extents. The reduced oligosaccharide Man8GlcNAcH2, obtained from IgM [Cohen, R. E. & Ballou, C. E. (1980) Biochemistry 19, 4345-4358], gave quasimolecular ion signals MNa+ at m/z 1544, MH+ at m/z 1522, MNa22+ at m/z 784, and MNa33+ at m/z 530, all corresponding to its assumed molecular weight of 1519.5. Mycobacterial methylmannose polysaccharides with the general structure ManxMeMany-OCH3 [Yamada, H., Cohen, R. E. & Ballou, C. E. (1979) J. Biol. Chem. 254, 1972-1979] were also successfully analyzed. Man1MeMan13-OCH3, the largest homolog, gave the expected signal of the quasimolecular ion MNa+ at m/z 2506. The larger polysaccharides were analyzed by using a KRATOS MS-50 mass spectrometer with a high-field magnet enabling full sensitivity to be maintained up to 3000 atomic mass units. Polysaccharides up to m/z 1978 were analyzed by using a KRATOS MS-9 mass spectrometer operated at 4 Kv. The signal-to-noise ratio, which becomes a serious problem in field desorption mass spectrometry at low accelerating voltages, and the low instrument sensitivity were improved considerably by our use of a method of adding scans with low total ion currents obtained over a longer desorption time. In this way, we obtained complete sequence information on methylmannose polysaccharides up to Man1MeMan9-OCH3(MNa+ at m/z 1802). Analysis of a presumed Man1MeMan7-OCH3, gave a spectrum consistent only with the structure Man2MeMan6-OCH3, revealing the existence of a methylmannose homolog with 2 unmethylated mannoses at the nonreducing end of the chain.
