Mass Spectrometry of Glycolipids

Glycolipids are ubiquitous constituents of cell membranes and are known to play a major role in cell-cell recognition. Much of the biological interest in 

The structural diversity and labile nature of the bonds that link the various building blocks have posed a serious challenge to the characterization of glycol-ipids. Complete structural characterization of GSLs requires structure elucidation of the constituents of the ceramide and sugar portions. In a classical mass spectrometry method, glycolipids are cleaved into individual structural units and are analyzed by EI-MS or GC/MS after conversion to a suitable derivative, such as by the acetylation, permethylation, or permethylation-reduction reaction. 

FAB and FAB-MS/MS have also played a major role in the analysis of GSLs [38] the negative-ion mode provides better results than the positive-ion mode. Improved spectral content is obtained in the positive-ion FAB mode only when glycolipids are converted to permethylated, peracetylated derivatives. FAB produces a sufficient number of fragment ions from which the structural 

and MALDI all have proven to be effective approaches to analyze gangliosides [45]. ECD and IRMPD of the ESI-produced molecular ions of gangliosides can provide important structural information [46]. To analyze minute amounts of biological samples, chip-based nano-ESI-MS and nano-MS/MS have been used to characterize gangliosides from human cerebellum [47]. Eigure 12.15, which is the MS/MS spectrum of the GTl species, demonstrates the usefulness of this approach. 

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Figure 11. Selected ion monitoring from mass spectrometry of glycolipids of epithelial cells of the two rat strains. A total of 200 fig each of the permethylated-reduced mixture was evaporated by a temperature rise of 5°C/min, and mass spectra were recorded each 38 sec. Electron energy was 34 eV, acceleration voltage 4 kV, trap current 500 fiA, and ion source temperature 290°C.

Costello, C. E. and Vath, J. E. Tandem mass spectrometry of glycolipids. Methods Enzymol, 193, 738, 1990. 

Figure 3. Selected ion monitoring from mass spectrometry of a permethylated-reduced mixture of non-acid glycolipids from non-epithelial residue of the white rat...

Otsuka, K. Yamakawa, T. The apphcation of droplet counter-current chromatography (DCC) forthe separation of acidic glycolipids. J. Biochem. (Tokyo) 1981,90,247-254. Kim, Y. Wang, T.C. Ma, Y.C. Liquid chromatography/ mass spectrometry of phosphohpids using electrospray ionization. Anal. Chem. 1994, 66, 3977. 

Although structures of these glycolipids were analyzed in the past by gas chromatography-mass spectrometry (GC-MS) of derivatives such as trimethylsilyl (TMS) ethers [14-16], the characterization in this work, which involves determination of the fatty acid composition and the location of double bonds in the long-chain base (Cw-sphingadienine), is carried out by B/E linked scan FAB mass spectrometry of the glycolipids itself... 

Neutral gangliolipids from Thermoplasma acidophilum were separated by PTLC, and their tentative structures were characterized by the combination of GC, H-NMR, and FAB-mass spectrometries [91]. The lipophilic portion of the neutral glycolipid was composed of caldarchaeol (dibiphytanyl-diglycerol tetraether), and the sugar moieties of the glycolipids were composed of glucose. 

Ramsay SL, Maire I, Bindloss C, Fuller M, Whitfield PD, Piraud M, Hopwood JJ, Meikle PJ (2004) Determination of oligosaccharides and glycolipids in amniotic fluid by electrospray ionisation tandem mass spectrometry in utero indicators of lysosomal storage diseases. Mol... 

Conventional electron impact or chemical ionization mass spectrometry requires that volatilization precede ionization and this is clearly a limiting factor in the analysis of many biochemically significant compounds. A newer ionization technique, field desorption (FD) (1, 2 ) removes this requirement and makes it possible to obtain mass spectrometric information on thermally unstable or non-volatile organic compounds such as glycoconjugates and salts. This development is particularly significant for those concerned with the analysis of glycolipids and we have therefore explored the suitability of field desorption mass spectrometry (FDMS) for this class of compounds. We have evaluated experimental procedures in order to enhance the efficiency of the ionization process and to maximize the information content of spectra obtained by this technique. 

Plasma-desorption mass spectrometry is another technique that has been applied successfully to the detection of readily removable fatty acyl substituents in intact glycolipids and their acylated derivatives. The specific location of the fatty acyl substituents in the ring of the glycosyl residues, as in LOS antigens, is determined by methylation under nonbasic conditions (see Section II.lb), followed successively by O-deacylation, ethylation of the exposed hydroxyl groups, and GC-MS analysis of partially alkylated alditol acetates21 ethyl groups denote the sites of previous O-acylation. 

Analytical methods for tocol analysis have continued to improve, as noted by Abidi (2000), and in the intervening ten years, as noted in this chapter. We predict that advances will continue to be made in the field of the chromatographic analysis of tocols. Also, we believe that lipidomic methods (quantitative analysis via direct injection tandem electrospray ionization mass spectrometry) will be developed for the rapid analysis of tocols, just as these methods have already been used for the profiling of phospholipids and glycolipids (Han, 2011 Welti, 2011). These methods usually involve the direct injection of lipid samples into a... 

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