Cf-252-plasma desorption mass spectrometry of unmodified lipid A: Fragmentation patterns and localization of fatty acids

The fragmentation patterns of synthetic Escherichia coli-type lipid A in pl asma desorption mass spectrometry (PDMS) in both negative- and positive-ion modes were determined. Negative-ion spectra gave signals for the main diph osphorylated (intact) molecular species in their native proportions. Intact and alkaline-treated lipid A in this mode gave, for the glucosamine I moie ty, easily identified signals that have not been previously reported in PDM S, These spectra gave enough information to localize the fatty acids. The p rocedure was verified with relatively homogeneous lipids A prepared from Sa lmonella minnesota R595 and Neisseria meningitidis lipopolysaccharides, and then applied to the previously unstudied Yersinia entercolitica O:11,24 li pid A to obtain the localization of its fatty acids. The possibility of obt aining this much information from two negative-ion spectra was attributed t o the method, described earlier, of preparing the samples. In the positive-ion mode, about half of the E. coli ions containing digluco samine appeared as monodephosphorylated species and/or as Na adducts. The i ntact glucosamine II moiety and its fragment ions gave signals none of whic h were Na adducts. With lipids A prepared from S. minnesota, N. meningitidi s, and Y. enterocolitica, similar fragmentation patterns were observed, For lipid A structure determination, the positive-ion mode could play a confir matory role, The above results and some of those reported by others were co mpared. Copyright (C) 1999 John Wiley & Sons, Ltd.