Direct analysis of glycolipids on thin-layer plates by matrix-assisted secondary ion mass spectrometry: application for glycolipid storage disorders

Loss of Dja2 accompanies pH deviation in lysosomes and lysosome-related organelles

The Dja2 knockout (Dja2-/- ) mice had respiratory distress, and >60% died within 2 days after birth. The surviving adult Dja2-/- mice were infertile and the lungs of Dja2-/- mice showed several abnormalities, including the processing defect of prosurfactant protein C in the alveolar epithelial type II cells and the accumulation of glycolipids in enlarged alveolar macrophages. The luminal pH of acidic organelles in Dja2-/- cells was shifted to pH 5.37-5.45. This deviated pH was immediately restored to control levels (pH 4.56-4.65) by the addition of a diuretic, ethyl isopropyl amiloride (EIPA). Although the role of DJA2 in maintaining the pH homeostasis of lysosome-related organelles is currently obscure, this rapid and remarkable pH resilience is best explained by an EIPA-sensitive proton efflux machinery that is disorganized and overactivated due to the loss of Dja2.

Sphingolipidoses in Morocco: Chemical profiling for an affordable and rapid diagnosis strategy

Sphingolipidoses are a group of metabolic diseases in which lysosomal hydrolases dysfunction disrupt normal sphingolipids' metabolism, leading to excess accumulation in cellular compartments and excretion in urine. These pathologies represent a significant burden among Moroccan population, for which an easy access to enzymatic assays and genetic tests is not guaranteed. Parallel analytical methods thus have to be developed for preliminary screening. In this study, 107 patients were addressed to the metabolic platform of the Marrakesh Faculty of Medicine for diagnosis confirmation. Thin-Layer Chromatography was used as a first step to perform chemical profiling of the patients' urinary lipids, allowing 36% of the patients to be efficiently oriented towards the adequate enzymatic assay. UPLC-MS/MS analyses of urinary sulfatides excreted in urines patient had been used to control the reliability of TLC analysis and to obtain more accurate information related to the sulfatides isoforms. This analytical process combining TLC with UPLC-MS/MS has enabled rapid and appropriate patient management in a reduced time and with reduced resources.

Advances on the compositional analysis of glycosphingolipids combining thin-layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single-method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high-performance thin-layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide-specific proteins, and (3) in situ MS analysis of protein-detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer-associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation.

Sphingolipidomics: methods for the comprehensive analysis of sphingolipids

Sphingolipids comprise a highly diverse and complex class of molecules that serve as both structural components of cellular membranes and signaling molecules capable of eliciting apoptosis, differentiation, chemotaxis, and other responses in mammalian cells. Comprehensive or "sphingolipidomic" analyses (structure specific, quantitative analyses of all sphingolipids, or at least all members of a critical subset) are required in order to elucidate the role(s) of sphingolipids in a given biological context because so many of the sphingolipids in a biological system are inter-converted structurally and metabolically. Despite the experimental challenges posed by the diversity of sphingolipid-regulated cellular responses, the detection and quantitation of multiple sphingolipids in a single sample has been made possible by combining classical analytical separation techniques such as high-performance liquid chromatography (HPLC) with state-of-the-art tandem mass spectrometry (MS/MS) techniques. As part of the Lipid MAPS consortium an internal standard cocktail was developed that comprises the signaling metabolites (i.e. sphingoid bases, sphingoid base-1-phosphates, ceramides, and ceramide-1-phosphates) as well as more complex species such as mono- and di-hexosylceramides and sphingomyelin. Additionally, the number of species that can be analyzed is growing rapidly with the addition of fatty acyl Co-As, sulfatides, and other complex sphingolipids as more internal standards are becoming available. The resulting LC-MS/MS analyses are one of the most analytically rigorous technologies that can provide the necessary sensitivity, structural specificity, and quantitative precision with high-throughput for "sphingolipidomic" analyses in small sample quantities. This review summarizes historical and state-of-the-art analytical techniques used for the identification, structure determination, and quantitation of sphingolipids from free sphingoid bases through more complex sphingolipids such as sphingomyelins, lactosylceramides, and sulfatides including those intermediates currently considered sphingolipid "second messengers". Also discussed are some emerging techniques and other issues remaining to be resolved for the analysis of the full sphingolipidome.

Analysis of neutral glycosphingolipids from Trypanosoma brucei

Neutral glycosphingolipids (GSLs) were isolated from Trypanosoma brucei and analyzed by thin-layer chromatography (TLC), TLC/secondary ion mass spectrometry (TLC/SIMS), and liposome immune lysis assay (LILA). Three species of neutral GSLs, designated as N-1, -2, and -3 were separated on TLC. N-1 GSL migrated very close to glucosylceramide (GlcCer) and N-2 GSL showed the same mobility as lactosylceramide (LacCer). On the other hand, the mobility of N-3 GSL on the TLC plate was slower than globotetraosylceramide (Gb4). In order to characterize the molecular species of neutral GSLs from T. brucei, N-1, -2 and -3 GSLs were analyzed by TLC/SIMS. The TLC/SIMS analysis of N-1 of the parasites revealed a series of (M-H)- ions from m/z 698 to 825 representing the molecular mass range of ceramide monohexoside (CMH) (GlcCer or galactosylceramide). On the other hand, the TLC/SIMS spectra of N-2 GSL revealed a series of (M-H)- ions from m/z 944-987 indicating the molecular mass range of LacCer. In the TLC/SIMS analysis of N-3 GSL, however, the characteristic molecular ions that can elucidate the structure of N-3 GSL were not obtained. In order to confirm the results obtained from TLC/SIMS, N-1, -2, and -3, GSLs were tested by LILA with specific antibodies against GlcCer, LacCer, and Gb4, respectively. N-1 GSL had reactivity to anti-GlcCer antibody and N-2 GSL reacted with the antibody against LacCer. However, N-3 GSL was not recognized by anti-Gb4 antibody. Using anti-GlcCer and anti-LacCer antibodies, furthermore, we studied the expression of GlcCer and LacCer in T. brucei parasites. Both GlcCer and LacCer were detected on the cell surface of T. brucei.

Structural Characterization of Neutral Glycosphingolipids by Thin-Layer Chromatography Coupled to Matrix-Assisted Laser Desorption/Ionization Quadrupole Ion Trap Time-of-Flight MS/MS

Rapid and convenient structural analysis of neutral glycosphingolipids (GSLs) was achieved by direct coupling of thin-layer chromatography (TLC) to matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-TOF) MS/MS. Positions of unstained GSL spots on developed TLC plates were determined by comparison to orcinol-stained references. A matrix solution of 2,5-dihydroxybenzoic acid (DHB) in acetonitrile/water (1:1 v/v) was then added directly to the unstained GSL spots, and the GSLs were directly analyzed by MALDI-QIT-TOF MS. The acetonitrile/water DHB solution proved to be suitable for MS/MS structural analysis with high sensitivity. MS/MS and MS/MS/MS of GSLs yielded simple and informative spectra that revealed the ceramide and long-chain base structures, as well as the sugar sequences. Hydroxy fatty acids in ceramide provided characteristic MS/MS fragment ions. GSLs were stained with primuline, a nondestructive dye, after TLC development, and successfully analyzed by MALDI-QIT-TOF MS/MS with high sensitivity. Immunostaining of GSLs after TLC development is a powerful method for characterizing antibody-specific sugars, but not ceramides. By coupling TLC-immunostaining of GSLs to MALDI-QIT-TOF MS/MS, we were able to identify both the sugar and the ceramide structures. The detection limits of asialo GM1 (Galbeta1-3GalNAcbeta1-4Galbeta1-4Glcbeta1-1'Cer) were 25 and 50 pmol in primuline staining and immunostaining, respectively.

A method for profiling gangliosides in animal tissues using electrospray ionization-tandem mass spectrometry

Gangliosides are critical in many functions of mammalian cells but present as a minor lipid component with many molecular species of subtle differences. Conventional strategies for profiling gangliosides suffer from poor reproducibility, low sensitivity, and low-throughput capacity. Prior separation of gangliosides by thin-layer chromatography and/or high-performance liquid chromatography not only was laborious and tedious but also could introduce uneven losses of molecular species. We developed a new strategy of using electrospray ionization-tandem mass spectrometry (ESI-MS/MS) to profile gangliosides with high-throughput potential. This strategy involves three new findings: (i) collision-induced fragmentation of gangliosides gave rise to a common ion of m/z 290, a derivative of N-acetylneuraminic acid; (ii) phospholipids exert a profound suppression of ganglioside detection in ESI-MS/MS to prevent a direct detection in total cellular lipid extracts; and (iii) enrichment of gangliosides in the aqueous phase from total cellular lipid extracts eliminates the damping effect of phospholipids and permits direct precursor scan.

Glycosphingolipid structural analysis and glycosphingolipidomics

Sphingosines, or sphingoids, are a family of naturally occurring long-chain hydrocarbon derivatives sharing a common 1,3-dihydroxy-2-amino-backbone motif. The majority of sphingolipids, as their derivatives are collectively known, can be found in cell membranes in the form of amphiphilic conjugates, each composed of a polar head group attached to an N-acylated sphingoid, or ceramide. Glycosphingolipids (GSLs), which are the glycosides of either ceramide or myo-inositol-(1-O)-phosphoryl-(O-1)-ceramide, are a structurally and functionally diverse sphingolipid subclass; GSLs are ubiquitously distributed among all eukaryotic species and are found in some bacteria. Since GSLs are secondary metabolites, direct and comprehensive analysis (metabolomics) must be considered an essential complement to genomic and proteomic approaches for establishing the structural repertoire within an organism and deducing its possible functional roles. The glycosphingolipidome clearly comprises an important and extensive subset of both the glycome and the lipidome, but the complexities of GSL structure, biosynthesis, and function form the outlines of a considerable analytical problem, especially since their structural diversity confers by extension an enormous variability with respect to physicochemical properties. This chapter covers selected developments and applications of techniques in mass spectrometric (MS) that have contributed to GSL structural analysis and glycosphingolipidomics since 1990. Sections are included on basic characteristics of ionization and fragmentation of permethylated GSLs and of lithium-adducted nonderivatized GSLs under positive-ion electrospray ionization mass spectrometry (ESI-MS) and collision-induced mass spectrometry (CID-MS) conditions; on the analysis of sulfatides, mainly using negative-ion techniques; and on selected applications of ESI-MS and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to emerging GSL structural, functional, and analytical issues. The latter section includes a particular focus on evolving techniques for analysis of gangliosides, GSLs containing sialic acid, as well as on characterizations of GSLs from selected nonmammalian eukaryotes, such as dipterans, nematodes, cestodes, and fungi. Additional sections focus on the issue of whether it is better to leave GSLs intact or remove the ceramide; on development and uses of thin-layer chromatography (TLC) blotting and TLC-MS techniques; and on emerging issues of high-throughput analysis, including the use of flow injection, liquid chromatography mass spectrometry (LC-MS), and capillary electrophoresis mass spectrometry (CE-MS).

Application of combined high-performance thin-layer chromatography immunostaining and nanoelectrospray ionization quadrupole time-of-flight tandem mass spectrometry to the structural characterization of high- and low-affinity binding ligands of Shiga toxin 1

Shiga toxin 1 (Stx1) represents an AB5 toxin produced by enterohemorrhagic Escherichia coli, which cause gastrointestinal diseases in humans that are often followed by potentially fatal systemic complications, such as acute encephalopathy and hemolytic uremic syndrome. The expression of the preferential Stx1 receptor, Gb3Cer/CD77 (Gal alpha1-4Gal beta1-4Glc beta1-1Cer), is one of the primary determinants of susceptibility to tissue injury. Due to the clinical importance of this life-threatening toxin, a combined strategy of preparative high-performance thin-layer chromatography (HPTLC) overlay assay and mass spectrometry was developed for the detection and structural characterization of Stx1-binding glycosphingolipids (GSLs). A preparation of neutral GSLs from human erythrocytes, comprising 21.4% and 59.1% of the high- and low-affinity Stx1-binding ligands Gb3Cer/CD77 and Gb4Cer, respectively, was separated on silica gel precoated HPTLC plates and probed for the presence of Stx1 receptors. Stx1 positive on the one hand and anti-Gb3Cer/CD77 and anti-Gb4Cer antibody positive bands from parallel reference runs on the other hand were extracted with chloroform/methanol/water (30/60/8, v/v/v). These crude extracts were used without any further purification for a detailed structural analysis by nanoelectrospray ionization quadrupole time-of-flight mass spectrometry (nanoESI-QTOF-MS) in the negative ion mode. In all extracts investigated, neutral GSLs were detected as singly charged deprotonated molecular ions, [M-H]-, and neither buffer-derived salt adducts nor coextracted contaminants from the overlay assay procedure or the silica gel layer were observed. For the structural characterization of Stx1- and antibody-binding GSLs low-energy collision-induced dissociation (CID) was applied to high and low abundant receptor species of the crude extracts. All MS/MS spectra obtained contained full series of Y-type ions, B-type ions and additional ions generated by ring cleavages of the sugar moiety. Only analytical quantities in the microgram scale of a single GSL species within the complex GSL mixture were required for the structural MS characterization of Stx1 ligands as Gb3Cer/CD77 and Gb4Cer. This effective combined HPTLC/MS procedure offers a broad range of applications, not only for toxins of bacterial origin, but also for any GSL-binding agents such as plant-derived lectins or human proteins with yet unknown binding specificities.

Direct Analysis of Silica Gel Extracts from Immunostained Glycosphingolipids by Nanoelectrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry

A combined strategy of preparative high-performance thin-layer chromatography overlay assay and mass spectrometry was established for the structural characterization of immunostained glycosphingolipids (GSLs) in silica gel extracts. Crude chloroform/methanol/water (30/60/8, v/v/v) extracts of immunostained TLC bands were analyzed by nanoelectrospray low-energy CID mass spectrometry without further purification. The GSL species investigated were isomeric monosialogangliosides of the neolacto series from a ganglioside preparation of human granulocytes, the disialoganglioside GD3 from a human melanoma lipid extract, and ganglio series Gg3Cer of a neutral GSL preparation from murine lymphoreticular MDAY-D2 cells. For the specific detection of lipid-bound oligosaccharides, polyclonal chicken IgY, murine monoclonal IgG3, and IgM antibodies were used. The resulting mass spectra show that only analytical quantities of approximately 1 microg of a single GSL within a complex mixture are required for the structure determination of immunostained GSLs by MS and MS/MS. All species investigated were detected as singly charged deprotonated molecular ions, and neither buffer-derived salt adducts nor coextracted contaminants from the immunostaining procedure or the silica gel layer were observed. This effective HPTLC-MS-joined procedure offers a wide range of applications for any carbohydrate binding agents such as bacterial toxins, plant lectins, and others.

Analysis of gangliosides from carp intestinal mucosa

The gangliosides of carp intestinal mucosa were isolated and analysed by thin-layer chromatography (TLC), TLC immunostaining test, and TLC/secondary ion mass spectrometry (TLC/SIMS). Four species of gangliosides, designated as G-1, G-2, G-3 and G-4, were separated on TLC. The TLC/SIMS analysis of the G-1 ganglioside of carp intestinal mucosa revealed a series of [M-H](-)ions from m/z 1061 to m/z 1131 representing the molecular mass range of GM4-like ganglioside with NeuAc. G-2, G-3 and G-4 gangliosides were analysed by the TLC immunostaining test. G-2 ganglioside was recognised by the monoclonal antibody specific for ganglioside GM1 (AGM-1 monoclonal antibody). However, G-3 ganglioside migrating on TLC between GM3 and GM1 ganglioside was not recognised by anti-GM3 monoclonal antibody and by AGM-1 monoclonal antibody. Furthermore, G-4 ganglioside with a similar TLC mobility as GD1a ganglioside did not show the reactivity to the anti-GD1a monoclonal antibody. In addition using the AGM-1 monoclonal antibody, the expression of GM1 ganglioside in the carp intestinal tissue was studied. GM1 ganglioside was detected on the epithelial cell surface of carp intestinal mucosa.

On-line overpressure thin-layer chromatographic separation and electrospray mass spectrometric detection of glycolipids

On-line thin-layer chromatographic separation and electrospray mass spectrometry (TLC/ESI-MS) has been accomplished by direct linking of a commercial overpressure TLC instrument, OPLC 50, and a Q-TOF mass spectrometer. Mass spectrometric detection sensitivity and chromatographic resolution achieved by this configuration were assessed using acidic glycolipids as examples. Under the optimized conditions, a sensitivity of 5 pmol of glycosphingolipid was readily demonstrated for TLC/ESI-MS and 20 pmol for TLC/ESI-MS/MS production scanning to derive the saccharide sequence and long chain base/fatty acid composition of the ceramide. Initial preconditioning of TLC plates is necessary to achieve high sensitivity detection by reducing chemical background noise. Plates can be used repeatedly (at least 10 times) for analysis, although this may result in a minor reduction in TLC resolution. Following solvent development, separated components on the TLC plates can be detected in the conventional way by nondestructive staining or UV absorption or fluorescence and can be stored for on-line TLC/ESI-MS analysis at a later stage without reduction in mass spectrometric detection sensitivity and chromatographic resolution. Aspects for further improvement of OPLC instrumentation include use of narrower TLC plate dimensions and refined design of the eluate exit system.

Direct electrospray-ionization mass spectrometric analysis of the major ganglioside from crucian carp liver after thin layer chromatography

Ganglioside patterns from crucian carp brain, muscle, and liver as well as liver gangliosides of roach, carp, the cichlid Oreochromis mossambicus, pigeon, dwarf hamster, and calf were comparatively analyzed by high performance thin layer chromatography (HPTLC). To achieve a rapid estimation on potentially interesting ganglioside compounds, electrospray-ionization mass spectrometry (MS) was directly applied to a chloroform/methanol extract of the major TLC band of crucian carp liver. The spectrum, obtained from a few micrograms of this crude biological sample, revealed a series of peaks corresponding to GM4-like monosialoganglioside species. GC-MS analysis revealed hydroxylated fatty acids ranging from 2 h 20 min:0 to 2 h 26 min:0 for the [M'H]- ions of m/z 1061-1145. Collision induced dissociation tandem MS/MS of the major peak with a [M'H]- ion of m/z 1117 demonstrated the presence of N-acetylneuraminic acid as sialic acid compound. The sugar composition was confirmed by GLC as galactose and sialic acid in a 1:1 molar ratio. Thus, the structure of the ion at m/z 1117 is N-acetylneuraminylgalactosylceramide (NeuAc-Gal-Cer) with the long chain base d18:1 and the hydroxylated fatty acid 2 h 24 min:0. The results demonstrate for the first time unambiguously that NeuAc-Gal-Cer is the main ganglioside fraction in fish liver and that electrospray ionization-mass spectrometry (ESI-MS) can be used to elucidate the chemical composition of a ganglioside fraction obtained by convenient extraction of a HPTLC band.

TLC blotting: application to microscale analysis of lipids and as a new approach to lipid-protein interaction

A simple method for the transfer of phospholipids and glycosphingolipids from a high-performance thin-layer chromatography (HPTLC) plate to a polyvinylidene difluoride (PVDF) membrane, called thin-layer chromatography (TLC) blotting, and its application in lipid research are described. Most of the lipids developed on the HPTLC plate are blotted quantitatively. Detection of the lipids on the membrane is done by chemical and immunological staining. This method makes it possible to purify individual lipid components separated on an HPTLC plate and to determine the structures of lipids in limited biological samples when combined with direct mass spectrometric analysis (TLC blotting/MS). A binding assay and the identification of ligands for microorganisms can be made using TLC blotting/MS. In addition, simple methods for the detection of enzymes on a substrate-immobilized PVDF membrane are described.

High-resolution thin-layer chromatography of gangliosides

In this review an updated overview of current improvements on thin-layer chromatography (TLC) of gangliosides over the past decade is provided. Basic general techniques and special advice is given for successful separation of glycosphingolipids. New approaches concerning continuous and multiple development, and several preparative TLC methods are also included. Emphasis is placed on TLC immunostaining and related techniques, i.e. practical applications of carbohydrate-specific antibodies, toxins and bacteria, viruses, lectins and eukaryotic cells. Thus, this review on ganglioside TLC summarizes its power as an analytical tool for a wide range of purposes.

High-energy collision-induced dissociation of ceramide ions from permethylated glycosphingolipids

Ceramide fragments from permethylated glycosphingolipids (GSLs) were studied by highenergy collision-induced dissociation (CID). In comparison with ceramlde fragments of underivatized GSLs, many more product ions including charge-remote fragment ions were observed. These ions provided detailed structural information on the ceramides. The relative intensity and the mass interval between the L and M ions were used to assign the position of the double bond. The position of the hydroxyl group was assigned with the Ln and K ions. Because the ceramide fragments and not the pseudomolecular ions were selected as the precursor ions, the size of GSLs had little effect on the quality of the product ion spectra. The sensitivity of this approach was in the range of picomoles.

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry of underivatized and permethylated gangliosides

Underivatized and permethylated gangliosides have been studied by the matrix-assisted laser desorption (MALO) ionization technique. The samples investigated included commercially available and highly purified gangliosides from the human brain containing up to five sialic acid residues. Several permethylated gangliosides have also been studied, and MALD has proven successful in analyzing multicomponent mixtures of glycolipids with different fatty acyl residues. During the studies a variety of matrix and wavelength combinations have been tested in both the positive and negative ion modes. The best results have been obtained with the matrices 2,5-dihyd roxybenzoic acid, 4-hydrazinobenzoic acid, 1,5-diaminonaphthalene, and 6-aza-2-thiothymine. Negative ion mass spectra of the underivatized gangliosides have always been of better quality than the positive ion mass spectra; exhibiting better signal-to-noise ratio, better resolution, less fragmentation, and less adduct formation with Na(+) and K(+). With increasing number of sialic acid substituents the molecular ion region became less and less resolvable leading to broadened peaks even in the negative ion mode. Fragmentation could frequently be observed in the negative ion mode, and it was pronounced in the positive ion mode. The major fragmentation pathways corresponded to loss of sialyl groupts) and to decarboxylation of one of the sialyl residues. For underivatized gangliosides the typical sample amount used was 10-20 pmol, Permethylation led to a significant improvement in sensitivity (two orders of magnitude); the detection limit of permethylated gangliosides was about 10 fmol. The higher stability of the permethylated compounds was indicated by the fact that positive ion mass spectra exhibited only a marginal extent of fragmentation.

Electron ionization-tandem mass spectrometry of glycosphingolipids. I: The identiftcation of compound-specific sequence ions in the collision-induced dissociation spectra of the immonium ions of two isomeric hexaglycosylceramides

A permethylated-reduced hexaglycosylceramide in a complex glycolipid mixture isolated from a unique human tissue has been identified by using tandem mass spectrometry (MS/MS). The mass spectrum of this glycolipid mixture, obtained by using in-beam electron ionization, is very complex, and fragment ions derived from the hexaglycosylceramide cannot be distinguished from other ions. Tandem mass spectrometry using a four-sector mass spectrometer gave the mass spectrum of the immonium ion of the permethylated-reduced hexaglycosykeramide (m / z 1645.8), which is characteristic of its structure. Comparison of this MS/MS spectrum with those of two similarly derivatized blood group hexaglycosylceramide isomers permitted identification of the unknown glycolipid structure.

The resolution into molecular species on desorption of glycolipids from thin-layer chromatograms, using combined thin-layer chromatography and fast-atom-bombardment mass spectrometry

Using a specially designed, motorised t.l.c.-f.a.b.-m.s. probe with continuous desorption and scanning over a moving t.l.c. plate, it was shown that glycolipids with identical carbohydrate sequences were well resolved into molecular species with differences in long-chain base and fatty acid. There was no serious diffusion of the glycolipids into the matrix. The technique is demonstrated for sulphatides (one and two sugar residues) isolated from human kidney, GM3 ganglioside isolated from human malignant melanoma, and chemically modified gangliotetraosylceramide from mouse intestine. T.l.c.-f.a.b.m.s. is convenient for sequencing and composition analysis of receptor-active glycolipids, the biological activity of which can be monitored in parallel by overlay on the t.l.c. plate with proteins, viruses, bacteria, or animal cells.

High-sensitivity structural analyses of oligosaccharide probes (neoglycolipids) by liquid-secondary-ion mass spectrometry

The sensitivity of detection and extent of information on structure obtainable by liquid-secondary-ion mass spectrometry (l.s.i.-m.s.) of neoglycolipids on the conventional target probe and directly from the surface of silica plates following t.l.c. has been assessed. Neoglycolipids were derived from malto-oligosaccharides, chitin oligosaccharides, and a range of deoxyhexose-, hexose-, 2-acetamido-2-deoxyhexose-, and sialic acid-containing mammalian oligosaccharides by reductive amination using phosphatidylethanolamine dipalmitoate (PPEADP). Sub-pmol amounts of the maltopentaose-PPEADP derivative applied directly to the target probe provided information on molecular weight, whereas approximately 1 pmol was required when analysed on the silica gel t.l.c. plate. With a biantennary octasaccharide derivative, the sensitivity of detection was 20-50 times lower and the other oligosaccharides had intermediate sensitivities. Information on composition and sequence was obtained readily from fragment ions, using 5 pmol of the maltopentaose derivative and 50 pmol of the octasaccharide derivative on the target probe, and 50 and 200 pmol, respectively, on the silica gel chromatogram. The optimised conditions formed the basis for characterising the structures of the components of mixtures of oligosaccharides generated from glycoproteins.

Desorption mass spectrometry of glycosphingolipids

Desorption mass spectrometry has become an important tool for sequencing and mapping of glycosphingolipids of natural, synthetic, or semi-synthetic origin. The appropriate combination of different desorption mass spectrometric techniques with other spectroscopic, enzymatic, chemical, and/or immunological methods represents the most direct and efficient way to establish frequent, yet unknown, molecular structure-function relationships.