Preparative isolation of cerebrosides (galactosyl and glucosyl ceramide)

Recent advances in the mass spectrometric analysis of glycosphingolipidome - A review

Aberrant expression of glycosphingolipids has been implicated in a myriad of diseases, but our understanding of the strucural diversity, spatial distribution, and biological function of this class of biomolecules remains limited. These challenges partly stem from a lack of sensitive tools that can detect, identify, and quantify glycosphingolipids at the molecular level. Mass spectrometry has emerged as a powerful tool poised to address most of these challenges. Here, we review the recent developments in analytical glycosphingolipidomics with an emphasis on sample preparation, mass spectrometry and tandem mass spectrometry-based structural characterization, label-free and labeling-based quantification. We also discuss the nomenclature of glycosphingolipids, and emerging technologies like ion mobility spectrometry in differentiation of glycosphingolipid isomers. The intrinsic advantages and shortcomings of each method are carefully critiqued in line with an individual's research goals. Finally, future perspectives on analytical sphingolipidomics are stated, including a need for novel and more sensive methods in isomer separation, low abundance species detection, and profiling the spatial distribution of glycosphingolipid molecular species in cells and tissues using imaging mass spectrometry.

Unusual fatty acid composition of cerebrosides from the filamentous soil fungus Mortierella alpina

The cerebrosides produced by the soil filamentous fungus Mortierella alpina strain KG-1/95 account for about 13% of the total polar lipids extractable from lyophilised cells with chloroform/methanol mixtures. By means of 1H NMR and (13)C NMR spectroscopy, matrix-assisted laser-desorption ionisation mass spectrometry, and chemical degradation experiment, they have been shown to be 1-O-beta-D-glucopyranosyl-2-N-(2'-D-hydroxyalkanoyl)-9-methylsphinga-4(E),8(E)-dienines, the fatty acid composition of which is unusual and consists of 2-hydroxytridecanoic (4%), 2-hydroxytetradecanoic (60%), 2-hydroxypentadecanoic (20%), and 2-hydroxyhexadecanoic (16%) acids.

A simple method for the synthesis of ceramides and radiolabeled analogues

A simple method has been developed for the coupling of amines to carboxylic acids. N-Fatty-acyl-sphingosine, cerebroside, and GM3, as well as their respective [14C] analogues, were synthesized using diethylphosphoryl cyanide as a potent coupling agent in the presence of triethylamine. The reaction procedure is rapid, racemization-free, and utilizes acids without derivatization. The desired ceramide products were obtained in 85-90% yield within one hour. The facile method presented here can also be used to synthesize [3H]-N-acyl-labeled, as well as [14C] [3H] double-labeled, ceramides.

Structure and properties of N-palmitoleoylgalactosylsphingosine (cerebroside)

Differential scanning calorimetry (DSC) and X-ray diffraction have been used to study the structure and properties of N-palmitoleoylgalactosylsphingosine (NPoGS; 16:1 galactocerebroside). DSC of fully hydrated NPoGS shows a complex pattern of three endothermic transitions at 35, 39 and 53 degrees C. Using a combination of thermal protocols (varying heating/cooling rates, incubation at different temperatures, etc.), the three ordered chain (gel) phases responsible for the transitions have been isolated; transition I (Tm = 35 degrees C; delta H(I) = 6.3 kcal/mol), transition II (Tm = 39 degrees C; delta HII = 8.6 kcal/mol), and transition III (Tm = 53 degrees C; delta HIII = 12.8 kcal/mol). The gel phases do not interconvert but rather form independently following cooling from the melted chain phase. X-ray diffraction data of the three isolated phases confirm that they all are bilayer structures with different bilayer periodicities (LI, 50.7 A; LII, 51.7 A; LIII = 49.2 A) and different chain packing modes. The LI, LII, and LIII bilayer phases each melt independently to the melted chain L alpha phase. Comparisons with other cerebrosides make it clear that alterations in chain length and chain unsaturation markedly affect the thermotropic behavior of cerebrosides and the metastable and stable phases they are able to form. As with phospholipids, introduction of cis-unsaturation into the N-acyl chain reduces both the chain melting temperature and enthalpy.

Phase properties of mixtures of ceramides

Ceramides have been proposed to have a central role in the function of the stratum corneum. Ceramides also influence the phase properties of model skin lipid mixtures, but the relevance of this to the stratum corneum function is controversial. Because the stratum corneum contains several classes of ceramides, the type of ceramides used in model mixtures of stratum corneum lipid lamellae may be important. Thus, the properties of alpha-hydroxy fatty acid containing (HFAC) and nonhydroxy fatty acid containing (NFAC) ceramides and their mixtures have been investigated. Ceramides were obtained by the conversion of purified bovine brain cerebrosides. Isolated, anhydrous HFAC underwent an endothermic solid to liquid transition at 92 degrees C. With hydration, an endothermic transition at 71.8 degrees C was observed which was accompanied by a reduction in the birefringence. The enthalpy increased from 66 to 89 J/g with a 20-d storage time. These thermal properties are very similar to those observed with hydroxy fatty acid containing cerebrosides. In contrast, anhydrous nonhydroxy fatty acid containing ceramides underwent a broad endothermic transition over the temperature range of 50-90 degrees C. When hydrated, the initial endothermic transition was interrupted by an exothermic transition that was followed immediately by a second endothermic transition. During these thermal changes, there was a loss of birefringence, and with completion of the second endothermic transition, a nonbirefringent liquid was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic effects of short-chain ceramide and glucosylceramide on sphingolipids and protein kinase C

Recent studies have identified a potential role for glucosylceramide (GlcCer) in growth promotion and hormonal signalling. In an effort to demonstrate a growth-promoting activity of GlcCer, we prepared a GlcCer having a short-chain acid (octanoyl), in the belief that this glycolipid could be absorbed more readily and more uniformly by cultured cells. By using a mixture of two specific lecithins, dioleoylglycerophosphocholine and 1-stearoyl-2-palmitoylglycerophosphocholine, we were able to prepare dispersions containing a high molar proportion of the GlcCer and the related ceramide, octanoyl sphingosine. Unexpectedly, both sphingolipids inhibited protein and DNA synthesis in Madin-Darby canine kidney cells and produced large increases in the levels of the natural lipids, GlcCer, ceramide, free sphingosine, and an amine that may be glucosylsphingosine (GlcSph). Decreases were seen in the level of sphingomyelin and the proportion of protein kinase C in the cell membranes. The level of lactosylceramide was diminished by octanoyl GlcCer but elevated considerably by octanoyl sphingosine. Diacylglycerols were increased by the lecithins in the liposomes, but the exogenous sphingolipids had no effect. Octanoyl sphingosine labeled in the sphingoid base yielded labeled GlcCer and sphingomyelin labeled in both long-chain and very-long-chain fatty acid families, as well as the octanoyl version. The two families of ceramides, however, had relatively little radioactivity. Some of these changes are attributed to rapid hydrolysis of the added lipids with the formation, particularly from the ceramide, of sphingosine and its anabolic metabolite, GlcSph. Several observations support the idea that the octanoyl sphingosine inhibited the phosphocholinetransferase that synthesizes sphingomyelin while the octanoyl GlcCer inhibited GlcCer beta-glucosidase and GlcCer galactosyltransferase. The use of unnatural short-chain lipids in the study of cell growth and other phenomena may result in unexpected changes in related metabolites and the findings from such experiments should therefore be interpreted cautiously.

Fluorescence assay of glucosylceramide glucosidase using NBD-cerebroside

A sensitive fluorometric assay for glucocerebroside beta-glucosidase [Dinur, T., Grabowski, G.A., Desnick, R.J., and Gatt, S. (1984) Anal. Biochem. 136, 223-234] has been reexamined. It was found that the lipids containing the NBD moiety (12-[N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)] used for standardization of the assay are light-sensitive and that the yield of fluorescent light is very sensitive to the composition of the solvent used in the fluorometric measurement. Some protection against fading could be obtained by adding a free-radical trapping agent, SlowFade. The fading of the free NBD-acid, when used for standardization, could be prevented by adding ethanol to the solvent, but this reduced the fluorescence yield. It is recommended that some of the fluorescent substrate be enzymatically hydrolyzed completely to NBD-ceramide, which can be utilized as the standard without the need to add ethanol. A warning about enzyme reaction rate stability with time is given, with a suggestion for ensuring constancy of activity.

Decreased formation of inositol trisphosphate in Madin-Darby canine kidney cells under conditions of beta-glucosidase inhibition

Recent work has demonstrated the enhancement of hormone-stimulated inositol trisphosphate formation in renal epithelial cells under conditions of glucosylceramide depletion. The role of glucosylceramide metabolism was explored further by exposing Madin-Darby canine kidney (MDCK) cells to the beta-glucosidase inhibitor conduritol B epoxide, which produced time-dependent and concentration-dependent increases in glucosylceramide levels and decreased bradykinin-stimulated inositol trisphosphate formation from isolated MDCK cell membranes. These data provide further support for an association between glucosylceramide levels and hormone-stimulated inositol trisphosphate formation.

Thermotropic phase properties of the hydroxyceramide/cholesterol system

The interaction of cholesterol with ceramides containing alpha-hydroxy fatty acyl chains (hydroxyceramides) has been studied as a foundation for characterizing the lipid bilayers of the stratum corneum. A relatively large quantity of cerebrosides was obtained from bovine brain and converted to ceramides through removal of the carbohydrate side chain. The ceramides were separated based on the absence or presence of hydroxy fatty acyl chains. The lyophilized hydroxyceramides showed a broad melting region at 92 degrees C. Hydroxyceramides dispersed in water produced a relatively narrow, thermotropic transition at 75 degrees C. The effect of cholesterol on this thermotropic phase transition of hydroxyceramides was determined by differential scanning calorimetry. With respect to the main transition, cholesterol caused a broadening of the phase transition at relatively low levels as well as a decrease in the peak transition temperature. The presence of cholesterol at levels in excess of 7 wt% gave rise to an additional low-temperature transition at 55 degrees C. Upon immediate rescanning, this transition was exothermic, but with increasing incubation time the area under the excess heat capacity curve as a function of temperature became smaller. After two days or more, the transition observed was endothermic. At cholesterol levels between 40 and 50 wt%, multiple peaks were observed. From comparisons with related systems, the cooperative thermal transitions of hydroxyceramides with cholesterol are suggested to result from changes in hydrogen bonding or be due to phase separation. The composition of isolated brain ceramides is being compared with that reported for the stratum corneum.

Glucosyceramide synthase of mouse kidney: further characterization with an improved assay method

The synthesis of glucosylceramide from ceramide and UDP-[3H]glucose by mouse kidney homogenates is very sensitive to the concentration of tissue. This was shown to be due to the presence of a UDP-glc pyrophosphatase, which could be blocked by adding NAD to the medium. A new solvent partitioning system is described, containing t-butyl methyl ether, isopropyl alcohol, and aqueous sodium sulfate, which separates the original substrate (UDP-[3H]glc) from the enzyme product, [3H]cerebroside. A particular advantage of the solvent system is that only a single partitioning step is needed, without backwashes, and the enzyme product appears in the upper phase, making transfer to a counting vial more reliable. A novel incubation device, a thermostatically controlled ultrasonic bath, is used to produce highly uniform enzyme reaction rates. Ca2+, as well as Mg2+ and Mn2+, was found to be a good stimulator of the glucosyltransferase. The enzyme activity in kidney of 22-day old mice, approximately 240 pmol/h/mg tissue, is significantly greater than previously demonstrated. The enzyme was stable in intact kidneys stored at -70 degrees C but unstable at 4 degrees C. The enzyme, when acting on endogenous ceramides, showed no demonstrable glucosylation of the C24 family of ceramides although this family is the predominant one in kidney.

Effects of D-threo-PDMP, an inhibitor of glucosylceramide synthetase, on expression of cell surface glycolipid antigen and binding to adhesive proteins by B16 melanoma cells

Incubating B16 melanoma cells with an inhibitor of glucosylceramide (GlcCer) synthetase, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-threo-PDMP), led to a considerable decrease in the levels of GlcCer and lactosylceramide (LacCer). The content of ganglioside GM3 was little affected, but the ability to bind a monoclonal antibody against the ganglioside (M2590) was greatly reduced, suggesting that the reduction in the simple glycolipids led to encryption of the membrane antigen. This interpretation is supported by the observation that permeabilization of the treated cells with Triton X-100 restored immunological reactivity. Specificity of the PDMP effect was shown by its lack of effect on the reactivity of two other surface antigens to anti-melanoma monoclonal antibodies M562 and M622, and of the major histocompatibility antigens to anti-H-2KbDb monoclonal antibody. The ability of the treated cells to attach to laminin or type IV collagen was lost but that to fibronectin was not. The effects of the enzyme inhibitor were counteracted by including GlcCer in the culture medium. This indicates that the lipid was absorbed by the cells and utilized like endogenously-formed GlcCer. Cells preattached to laminin or collagen could be induced to round up by addition of inhibitor. In contrast, L-threo-PDMP (which does not block the synthesis of GlcCer) had no effect on the immunologic reactivity of GM3 or the adhesion properties of the cells. However, it did produce considerable accumulation of LacCer. These data suggest that the simple glycolipid, GlcCer, is an essential factor for antigenic expression of the more complex glycolipids on cell surfaces and that there is a close association and interaction between glycolipids and adhesive receptors on the cell surface.

Intermixing of dipalmitoylphosphatidylcholine with phospho- and sphingolipids bearing highly asymmetric hydrocarbon chains

We have used high-sensitivity differential scanning calorimetry to investigate the mixing of dipalmitoylphosphatidylcholine (DPPC) with N-lignoceroylgalactocerebroside, N-lignoceroylsulfogalactocerebroside and 1-lauroyl-2-lignoceroylphosphatidylcholine. These three lignoceroyl species, whose two hydrocarbon chains are quite discrepant in length, are completely miscible with DPPC in the liquid-crystalline state. Mixtures of all three lignoceroyl lipids with DPPC show phase separation in the gel state, which is observed over a limited range of compositions (from less than 10 mol% to just over 40 mol% sulfatide) in the case of N-lignoceroylsulfatide and over a wide range of compositions in the cases of N-lignoceroylcerebroside (less than 10 mol% to greater than 90 mol% cerebroside) and 1-lauroyl-2-lignoceroyl-PC (roughly 10 mol% to 90 mol% lauroyl/lignoceroyl PC). The extensive solid-solid phase separation observed in mixtures of DPPC and 1-lauroyl-2-lignoceroyl-PC, which show eutectic behavior, is somewhat unexpected given the similar transition temperatures of the two components but appears to reflect the ability of the lignoceroyl species to form an interdigitated gel phase. However, we find no evidence that the N-lignoceroylsphingolipids are markedly more prone to segregate laterally in PC-rich bilayers than are previously studied sphingolipid species with shorter N-acyl chains. We suggest on the basis of these results that the primary biological importance of the very long N-acyl chains found in many sphingolipids may lie in some function other than the promotion of lateral segregation of sphingolipid-enriched domains in biological membranes.

Normalization of liver glucosylceramide levels in the "Gaucher" mouse by phosphatidylserine injection

A model of the human genetic disorder, Gaucher disease, can be rapidly generated in mice by the injection of emulsified glucosylceramide and an inhibitor of the lipid's hydrolase, conduritol B epoxide. The liver grows rapidly as it absorbs the load of lipid but the effect disappears as new glucosidase is formed and the load is hydrolyzed. This normalization process is accelerated by treatment with phosphatidylserine, which is a known stimulator of the enzyme. It is possible that injecting the phospholipid into Gaucher patients would have a therapeutic effect since it might help them utilize their residual glucosidase to destroy stored glycolipid.

Hydrolysis of galactosylsphingosine and lactosylsphingosine by beta-galactosidases in human brain and cultured fibroblasts

Enzymatic properties of beta-galactosidases with galactosylsphingosine (psychosine) and lactosylsphingosine as the substrates were examined. Although bile salts were stimulatory on the hydrolysis of the glycolipids in normal brain and cultured fibroblasts, the hydrolytic activities could be readily assayed, without detergents. The in vitro hydrolysis of lactosylsphingosine in cultured fibroblast homogenates was catalyzed by two enzymes, as is the case with the hydrolysis of galactosylceramide and lactosylceramide. Lactosylsphingosine beta-galactosidase activities assayed in the absence and the presence of taurocholate (probably lactosylceramidase I) were deficient in fibroblasts from patients with globoid cell leukodystrophy, while the activity assayed with sodium cholate (probably lactosylceramidase II) was deficient in GM1 gangliosidosis fibroblasts. In contrast, galactosylsphingosine beta-galactosidase was not activated by cholate and the enzyme activities assayed with the no-additive and taurocholate systems were deficient in brain and fibroblasts from patients with globoid cell leukodystrophy, thereby indicating that the hydrolysis of galactosylsphingosine is catalyzed by one enzyme, galactosylceramidase I. Exogenous lipids and an activator protein purified from normal spleen activated galactosylsphingosine beta-galactosidase but they were inhibitory to lactosylsphingosine beta-galactosidase. Because the Km values of lactosylsphingosine beta-galactosidase assayed with cholate were several magnitude higher than those obtained with the no-additive system and because lactosylsphingosine is readily hydrolyzed with the no-additive system in vitro, it is likely that the in vivo hydrolysis of the lipid is catalyzed by only one enzyme, lactosylceramidase I.

Structure and metastability of N-lignocerylgalactosylsphingosine (cerebroside) bilayers

Differential scanning calorimetry (DSC) and X-ray diffraction have been used to study hydrated N-lignocerylgalactosylsphingosine (NLGS) bilayers. DSC of fully hydrated NLGS shows an endothermic transition at 69-70 degrees C, immediately followed by an exothermic transition at 72-73 degrees C; further heating shows a high-temperature (Tc = 82 degrees C), high-enthalpy (delta H = 15.3 kcal/mol NLGS) transition. Heating to 75 degrees C, cooling to 20 degrees C and subsequent reheating shows no transitions at 69-73 degrees C; only the high-temperature (82 degrees C), high-enthalpy (15.3 kcal/mol) transition. Two exothermic transitions are observed on cooling; for the upper transition its temperature (about 65 degrees C) and enthalpy (about 6 kcal/mol NLGS) are essentially independent of cooling rate, whereas the lower transition exhibits marked changes in both temperature (30----60 degrees C) and enthalpy (2.2----9.5 kcal/mol NLGS) as the cooling rate decreases from 40 to 0.625 Cdeg/min. On reheating, the enthalpy of the 69-70 degrees C transition is dependent on the previous cooling rate. The DSC data provide clear evidence of conversions between metastable and stable forms. X-ray diffraction data recorded at 26, 75 and 93 degrees C show clearly that NLGS bilayer phases are present at all temperatures. The X-ray diffraction pattern at 75 degrees C shows a bilayer periodicity d = 65.4 A, and a number of sharp reflections in the wide-angle region indicative of a crystalline chain packing mode. This stable bilayer form converts to a liquid-crystal bilayer phase; at 93 degrees C, the bilayer periodicity d = 59.1 A, and a diffuse reflection at 1/4.6 A-1 is observed. The diffraction pattern at 22 degrees C represents a combination of the stable and metastable low-temperature bilayer forms. NLGS exhibits a complex pattern of thermotropic changes related to conversions between metastable (gel), stable (crystalline) and liquid-crystalline bilayer phases. The structure and thermotropic properties of NLGS are compared with those of hydrated N-palmitoylgalactosylsphingosine reported previously (Ruocco, M.J., Atkinson, D., Small, D.M., Skarjune, R.P., Oldfield, E. and Shipley, G.G. (1981) Biochemistry 20, 5957-5966).

The interactions of 1-palmitoyl-2-oleylphosphatidylcholine and bovine brain cerebroside

Model membranes composed of 1-palmitoyl-2-oleylphosphatidylcholine (POPC) and bovine brain galactocerebroside (BOV-CER) have been studied by differential scanning calorimetry (DSC). POPC is a naturally occurring phospholipid, and BOV-CER is a major component of the myelin membrane. POPC and BOV-CER are immiscible in the gel state over the composition range 0-70 mol% BOV-CER. At most POPC/BOV-CER ratios, broad dual-peaked acyl chain transitions are observed, characteristic of the co-existence of a fluid POPC-rich liquid-crystalline phase and a solid BOV-CER-rich gel phase over a wide temperature range.

The effects of ethylene glycol and dimethyl sulfoxide on cerebroside metastability

Aqueous dispersions of n-acyl cerebrosides are known to exhibit metastable polymorphism of the type: (Formula: see text). The involvement of hydration in this metastable polymorphism has been investigated by differential scanning calorimetric studies of aqueous palmitoylgalactocerebroside (C16:0-CER) dispersions in the presence of agents which disrupt water structure. In the presence of 50 vol% ethylene glycol or 50 vol% dimethyl sulfoxide, only a single reversible ordered----liquid-crystalline transition is observed. This single ordered----liquid-crystalline transition exhibits a smaller enthalpy and occurs at a lower temperature than the major Polymorph II----liquid-crystal transition observed for dispersions in water alone. These results indicate that metastable polymorphism in C16:0-CER is related to hydration.

Brain cerebrosides: preparative purification using a new chromatographic support--magnammsil

A preparative method for isolation and purification of cerebrosides from bovine brain is described. A crude cerebroside fraction is precipitated with ether from a chloroform-methanol extract and purification is achieved by column chromatography on a new column support, "magnammsil." A partial separation of hydroxy and nonhydroxy cerebrosides is achieved. The method is more economical for a large-scale preparation than previously published methods.

Synthesis of a fluorescent derivative of glucosyl ceramide for the sensitive determination of glucocerebrosidase activity

A fluorescent derivative of glucosyl ceramide was synthesized by covalently linking a fluorescent fatty acid, 12-[N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)] aminododecanoic acid to the amino group of sphingosyl-1-O-beta-D-glucoside, glucosyl sphingosine. For hydrolysis by glucocerebrosidase, this substrate was dispersed in mixed micelles with Triton X-100 and sodium taurocholate or in unilamellar liposomes with phosphatidylcholine and the negatively charged lipid, dicetylphosphate. In either micellar or liposomal dispersions of the fluorescent substrate, reaction rates were linear with time and protein concentration, and saturation kinetics were observed. The rate of hydrolysis of this fluorescent substrate was equal to that obtained with radiolabeled glucosyl ceramide. The fluorescent glucosyl ceramide was used to determine glucocerebrosidase activity in extracts of human leukocytes, cultured skin fibroblasts, and various tissues as well as in partially purified splenic and placental glucocerebrosidase preparations. This fluorescent derivative of the natural substrate was not hydrolyzed by aryl beta-glucosidase(s), thereby facilitating the specific and reliable diagnosis of heterozygotes and homozygotes with Gaucher disease.

Physical studies of cell surface and cell membrane structure. Deuterium nuclear magnetic resonance studies of N-palmitoylglucosylceramide (cerebroside) head group structure

Deuterium Fourier-transform nuclear magnetic resonance spectra of N-palmitoyl[2,3,4,6,6-2H5]glucosylceramide, N-palmitoyl[1-2H]glucosylceramide, N-palmitoyl-[5,6,6-2H3]glucosylceramide, and N-palmitoyl[6,6-2H2]-glucosylceramide have been obtained at 55.3 MHz (corresponding to a magnetic field strength of 8.5 T) for lipids as multilamellar dispersions in excess water at 90 degrees C, above the gel to liquid-crystal phase transition temperature (Tc = 82 degrees C). Spectra were also obtained for these same lipids dispersed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, and cholesterol, all in excess water at 90 degrees C. The results are analyzed in terms of a model in which the lipid undergoes fast axial diffusion, together with a "wobbling" of the polar head group, by mathematical methods similar to those used previously for the choline and ethanolamine head groups in phosphatidylcholines and phosphatidylethanolamines [Skarjune, R., & Oldfield, E. (1979) Biochemistry 18, 5903--5909]. However, contrary to the results obtained in the previous study, which indicated many possible conformations for the choline and ethanolamine head groups, results with labeled cerebrosides yield at most a few orientations for the glucose head group in each of the systems studied. Furthermore, where multiple solutions do occur, they fall within a narrow orientational subspace so that all solutions exhibit the same general features. We also show that the order parameter describing the head group wobble is fully determined for each system, and it indicates a rather mobile structure for the cerebroside head group, in a variety of environments. In each system studied the polar head group projects essentially straight up from the bilayer surface into the aqueous region, thereby permitting maximum hydration of the four glucose hydroxyl groups by bulk water molecules.

Experimental allergic neuritis. I. Rat strain differences in the response to bovine myelin antigens

Strain differences among rats to the induction and severity of experimental allergic neuritis (EAN) in response to whole PNS myelin were observed. Lewis rats were highly susceptible and developed severe EAN without central nervous system lesions (EAE), while Brown Norway rats were most resistant. Wistar, Sprague-Dawley, and Buffalo rats were susceptible but developed less severe disease than Lewis rats. Only Lewis rats consistantly developed EAN in response to isolated P2 protein. The severity of EAN was enhanced by treatment of the P2 with mercaptoethanol prior to injection. None of the strains developed EAN in response to galactocerebroside and none developed the lesions of EAE in response to any of the bovine myelin antigens tested. Myelin protein profiles from these rat strains were similar which suggests that factors other than target tissue differences, such as genetically determined immune responses to bovine myelin antigens, must be involved in these differing responses.

Physical studies of cell surface and cell membrane structure. Deuterium nuclear magnetic resonance investigation of deuterium-labelled N-hexadeconoylgalactosylceramides (cerebrosides)

1. Deuterium Fourier transform nuclear magnetic resonance spectra of a series of N-palmitoylgalactosylceramides (cerebrosides) specifically labelled with deuterium at one of positions 2', 6', 10' and 16' of the acyl chain, or in the C-6 hydroxymethyl group of the galactose residue, have been obtained using a spin-echo technique at 34.1 MHz with a homebuilt superconducting magnet spectrometer. 2. The effects of temperature and cholesterol on the deuterium spectra have been investigated. The results indicate, when compared at the same reduced temperature, that the hydrocarbon chain organization in the liquid crystalline phase of palmitoylgalactosylceramide is essentially identical to that seen in similar chain length glycerophospholipids. In particular, two sets of quadrupole splittings are seen for a 2'-labelled N-palmitoylgalactosylceramide, indicating non-equivalent deuterons as noted previously for phospholipids. 3. Two sets of quadrupole splittings are observed for the headgroup C-6-labelled N-palmitoylgalactosylceramide. It is proposed that these signals arise from the enantiomeric R and S lipids, and that motion of the hydroxymethyl group is slow (greater than 10(-5) S). These results suggest the presence of a hydrogen bond network in the polar headgroup region. 4. The effects of cholesterol on the deuterium spectra of N-palmitoylgalactosylceramide-labelled as C2H3 in the terminal methyl group, at 1:1 mol ratios and in excess water below the crystal to liquid-crystal phase transition temperature (Tc) of the pure lipid (82 degrees C), are different to the effects seen with the phosphatidylcholine-cholesterol system. The spectra below Tc are characterised by two overlapping powder patterns, one with a quadrupole splitting of approx. 6 kHz (fluid liquid-crystalline phase) and one with a quadrupole splitting of about 20--25 kHz (crystal or gel-state lipid). Exchange between these two environments is therefore slow, leading to the possibility of characterising the cerebroside-cholesterol phase diagram using deuterium nuclear magnetic resonance spectroscopy.