Hydration of N-palmitoylgalactosylsphingosine compared to monosaccharide hydration

Differential scanning calorimetry (DSC) studies of the ice-water transition of N-palmitoylgalactosylsphingosine (NPGS) (cerebroside)/water mixtures indicate 4 +/- 1 non-freezable water molecules per molecule NPGS. This hydration level, representing strongly bound water, is identical to that observed previously for human glucocerebroside (Bach, D., Sela, B. and Miller, I.R. (1982) Chem. Phys. Lipids 31, 381). Comparison of gluco- and galacto-cerebroside hydration with hydration measurements on simple monosaccharides suggests a favored orientation of the glycosyl polar group at the cerebroside-water interface.

Impaired cerebroside sulfate hydrolysis in fibroblasts of sibs with "pseudo" arylsulfatase A deficiency without metachromatic leukodystrophy

Low arylsulfatase A levels are reported in two siblings, one with a neurologic disability not typical for metachromatic leukodystrophy, the other a healthy 18-year-old female with a normal developmental history. In both individuals, arylsulfatase A levels in white blood cells were 7-8% of control values. Cultured fibroblasts gave low values (8-10% of normal) for both cerebroside sulfatase and arylsulfatase A activities. Other family members had enzyme levels consistent with heterozygote or normal status. Cerebroside sulfate loading tests of cultured fibroblasts in 199-CO2 media were normal for all family members who were tested. In MEM-HEPES media, however, cells from the two arylsulfatase A deficient siblings showed attenuated sulfolipid catabolism. Additional clinical and laboratory studies on these individuals failed to demonstrate any features suggestive of metachromatic leukodystrophy, i.e., normal nerve conduction velocities, normal sural nerve biopsy results, and normal urinary sulfatide excretion. It is concluded that the neurologic abnormalities in the one sibling are not the result of the low enzyme activity and that both individuals represent examples of pseudo arylsulfatase A deficiency (arylsulfatase A deficiency without metachromatic leukodystrophy). These results thus call into question the ability of the high-sensitivity cerebroside sulfate loading test as carried out in MEM-HEPES media to differentiate pathologically significant defects i.e., metachromatic leukodystrophy from benign "pseudo-deficiencies."

Compositional aspects of lipid hydration

The effect of various lipids such as cerebrosides, gangliosides and dipalmitoyl lecithin (DPPC) on the lowering of the melting temperature of water, was determined by differential scanning calorimetry (DSC). The lowering of the melting temperature, and the number of water molecules per lipid molecule which apparently do not undergo melting, increase with the increase of the size and charge of the polar group and with the unsaturation of the hydrocarbon chains. Freezing curves show supercooling to about -20 degrees C. It was found that the number of apparently unfreezable water molecules is about four for glucocerebroside from Gaucher's spleen and about eight or nine for galactocerebroside from bovine brain. In gangliosides from bovine brain the following number of water molecules/lipid molecule are apparently unfreezable: 22-30 in GM1, 33-40 in GD1a + GD1b while a fraction of gangliosides containing 75% GQ1b and 25% GT1b affects up to 60 molecules of water/molecule of lipid. A zwitterionic DPPC molecule removes apparently six to seven water molecules from freezing. There is no indication that the apparently unfreezable water molecules are in a distinct state. It is suggested that they freeze at very low temperatures producing a flat tail preceding the transition peak which cannot be discerned from the base line.

Diagnosis of metachromatic leukodystrophy, Krabbe disease, and Farber disease after uptake of fatty acid-labeled cerebroside sulfate into cultured skin fibroblasts

[(14)C]Stearic acid-labeled cerebroside sulfate (CS) was presented to cultured skin fibroblasts in the media. After endocytosis into control cells 86% was readily metabolized to galactosylceramide, ceramide, and stearic acid, which was reutilized in the synthesis of the major lipids found in cultured fibroblasts. Uptake and metabolism of the [(14)C]CS into cells from typical and atypical patients and carriers of metachromatic leukodystrophy (MLD), Krabbe disease, and Farber disease were observed. Cells from patients with late infantile MLD could not metabolize the CS at all, while cells from an adult MLD patient and from a variant MLD patient could metabolize approximately 40 and 15%, respectively, of the CS taken up. These results are in contrast to the in vitro results that demonstrated a severe deficiency of arylsulfatase A in the late infantile and adult patient and a partial deficiency (21-27% of controls) in the variant MLD patient. Patients with Krabbe disease could metabolize nearly 40% of the galactosylceramide produced in the lysosomes from the CS. This is in contrast to the near zero activity for galactosylceramidase measured in vitro. Carriers of Krabbe disease with galactosylceramidase activity near half normal in vitro and those with under 10% of normal activity were found to metabolize galactosylceramide in cells significantly slower than controls. This provides a method for differentiating affected patients from carriers with low enzyme activity in vitro. Cells from patients with Farber disease could catabolize only approximately 15% of the ceramide produced from galactosylceramide. This technique provides a method for the identification of typical and atypical patients and carriers of three genetic diseases using one substrate.

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.

Presymptomatic diagnosis: metachromatic leukodystrophy or pseudo arylsulphatase A deficiency?

Diagnosis of metachromatic leukodystrophy (MLD) was established in the proband at age 27 months. An examination of the family arylsulphatase A profile revealed that the father and younger sibling, age 2 months, had very low enzyme activities like the proband. The father, in all likelihood, had the pseudo arylsulphatase A deficiency trait, but the sibling could be either pseudodeficient or affected with MLD. The fibroblast cerebroside sulphate loading test confirmed that the father had pseudo arylsulphatase A deficiency. The test also indicated that the sibling was affected with MLD. This was confirmed by clinical evidence of neurological degeneration by 18 months.

Cerebroside sulfotransferase in rat gastric mucosa

1. Cerebroside sulfotransferase activity was demonstrated in rat gastric mucosa. This enzyme preparation catalyzes the transfer of sulfate group from 3'-phosphoadenosine-5'-phosphosulfate to added cerebroside and lactosylceramide. 2. Psychosine also serves as an acceptor for sulfate group. 3. Both hydroxy-fatty acid and non-hydroxy-fatty acid containing cerebrosides are equally sulfated. However, this enzyme is inactive toward glucosylceramide. 4. The optimum pH is around 6.0. The reaction is stimulated by the addition of 0.4-0.9% of Triton X-100. 5. The presence of 2-4 mM ATP moderately stimulates the reaction, but is inhibitory when the concentration exceeds 6 mM. 6. EDTA has no effect. 7. Both Mg2+ and Ca2+ stimulate at lower concentrations (less than 16 mM), but inhibit at higher concentrations (greater than 20 mM). Mn2+, however, is a strong inhibitor even at 8 mM concentration. 8. The apparent Km for cerebroside is 0.04 mM, while that for 3'-phosphoadenosine-5'-phosphosulfate is 0.45 microM.

X-ray diffraction and calorimetric study of anhydrous and hydrated N-palmitoylgalactosylsphingosine (cerebroside)

Differential scanning calorimetry and X-ray diffraction of anhydrous and hydrated N-palmitoylgalactosylsphingosine (NPGS) show evidence of complex polymorphic behavior and interconversions between stable and metastable structural forms. Anhydrous NPGS exhibits three lamellar crystal forms (A, B, and B') at temperatures below 143 degrees C and a liquid-crystal form between 143 and 180 degrees C before melting to an isotropic liquid at 180 degrees C. The crystal B leads to liquid-crystal transition is accompanied by an enthalpy change, delta H, of 11.2 kcal/mol of NPGS, while a relatively small enthalpy change (delta H = 0.8 kcal/mol) marks the liquid-crystal leads to liquid transition. The A and B' crystal forms do not hydrate readily at room temperature. When heated, crystal form A in the presence of water undergoes an exothermic transition at 52 degrees C to produce a thermodynamically stable hydrated crystal E form. X-ray diffraction shows that this stable bilayer crystal form has a highly ordered hydrocarbon chain packing arrangement; melting to the bilayer liquid-crystal form occurs at 82 degrees C with a large enthalpy change, delta H = 17.5 kcal/mol of NPGS. A complex liquid-crystal leads to crystal transition is observed on cooling; the cooling rate independent exotherm involves the transition of the hydrated liquid crystal to an intermediate metastable crystal form identical with anhydrous crystal form A. The subsequent cooling rate dependent step involves the conversion of the metastable crystal form A to the stable crystal form E. We suggest that hydrated crystal form E is stabilized by both a highly ordered chain packing mode and a lateral intermolecular hydrogen bonding network involving the sphingosine backbone, the galactosyl group, and interbilayer water molecules. Although disruption of both the specific hydrogen chain packing and H-bonding networks occurs at the high enthalpy transition to the bilayer liquid-crystal L alpha form, these two types of interactions are not reestablished simultaneously on cooling. First, recrystallization of the hydrocarbon chain accompanies removal of water from the lipid interface, leading to "dehydrated" metastable crystal form A. This is followed by a time-dependent, temperature-dependent hydration process which allows a rearrangement of the hydrogen-bonding matrix. Alterations in the NPGS-NPGS and NPGS-water interactions accompany further changes in the hydrocarbon chain packing and lead to the formation of the stable E form.

Haptenic activity of galactosyl ceramide and its topographical distribution on liposomal membranes. I. Effect of cholesterol incorporation

The relation between the immune-reaction of phosphatidylcholine liposomes containing spin-labeled galactosyl ceramide with or without cholesterol and the topographical distribution of the glycolipid in membranes was studied. In egg yolk phosphatidylcholine liposomes, both immune agglutination and antibody binding occurred, irrespectively of the presence of cholesterol, though the motion of the fatty acyl chain of spin-labeled galactosyl ceramide was restricted by cholesterol. In dipalmitoyl phosphatidylcholine liposomes, unlike in egg yolk phosphatidylcholine liposomes, the immune-reaction depended on the cholesterol content. The electron spin resonance (ESR) spectra of spin-labeled galactosyl ceramide in dipalmitoyl phosphatidylcholine liposomes indicated that cholesterol affected the topographical distribution of spin-labeled galactosyl ceramide in the liposomes. Without cholesterol, most of the spin-labeled galactosyl ceramide was clustered on the dipalmitoyl phosphatidylcholine membrane, but with increase of cholesterol, random distribution of hapten on the membrane increased. The cholesterol-dependent change in the topographical distribution of hapten on the membranes was parallel with that of immune reactivity. 'Aggregates' composed solely of galactosyl ceramide did not show any binding activity with antibody. The findings suggest that the recognition of galactosyl ceramide by antibody depended on the topographical distribution of hapten molecules. Phosphatidylcholine and/or cholesterol may play roles as 'spacers' for the proper distribution of 'active' haptens on the membranes. The optimum density of haptens properly distributed on liposomal membranes is discussed.

Hydrophobic compounds interfere in radioimmunoassay for basic protein in myelin

Hydrophobic compounds influenced the accuracy of the radioimmunoassay for myelin basic protein when lipids (stearic acid, phosphatidylcholine, cholesterol, cerebroside, sulfatide, or GM1 ganglioside) or proteolipids (white-matter proteolipid apoprotein, kidney proteolipid apoproteins, or heart proteolipid apoproteins) were added to a known amount of basic protein and the samples assayed. All of these interfere with the assay, but the direction of the error depends on the quantity added: low concentrations of lipid decrease apparent basic protein, high concentrations enhance it. Obviously, results of basic-protein assays must be interpreted carefully.

[Ion permeability of cerebroside and sphingomyelin bilayer membranes]

Ionic conductivity of bilayer membranes formed of cerebrosides and sphingomeylins isolated from bovine brains and its dependence on medium pH were studied. It was found that conductivity of the membranes from cerebrosides in KC1, CaCl2 solutions is 2-3 orders, and from sphingomyelin 1-2 orders higher than that of bilayers from lecithin and phospholipids. Both in cerebroside and sphingomyelin membranes the conductivity depended on medium pH, unlike the bilayer membranes of the brain and liver phospholipids.

[Certain physical parameters of cerebroside and phospholipid-cerebroside membranes]

Study of some electric properties of bilayer membranes made of cerebrosides and phospholipid-cerebroside mixture has shown that the capacity of cerebroside film is lower than that of lecithin-cerebroside and phospholipid-cerebroside ones (0.22 +/- 0.01 mkf/cm2 and 0.28 +/- 0.01 mkf/cm2 respectively). The membranes had small cation selectivity. It is stated that conductivity of cations of mixed phospholipid-cerebroside membrane is two orders, and of cerebroside three orders higher than that of phospholipid bilayers. Conductivity of the films under study depends on the medium pH. By means of fluorescent probes cerebrosides were found capable of changing the conformation of phospholipid membranes.

Molecular conformations of cerebrosides in bilayers determined by Raman spectroscopy

Vibrational Raman spectra of the solid and gel phases of bovine brain cerebrosides and the component fractions, kerasin and phrenosin, provide conformational information for these glycosphingolipids in bilayer systems. The carbon-carbon stretching mode profiles (1,150-1,000 cm-1) indicate that at 22 degrees C the alkyl chains assume an almost all-trans arrangement. These spectral data, combined with those from the C-H stretching region (3,050-2,800 cm-1), show that phrenosin forms the most highly ordered polycrystalline solid and kerasin the most ordered gel phase. The conformation of the unsaturated, 24-carbon acyl chains is monitored independently by a skeletal stretching mode at 1,112 cm-1. The alkyl chains in the kerasin and phrenosin gels are sufficiently extended to allow interdigitation of the 24-carbon acyl chains across the midplane of the bilayer. The amide I vibrational mode occurs at a lower frequency in solid phrenosin than kerasin, a shift consistent with stronger hydrogen bounding. This band is broadened and shifted to higher frequencies, however, in the phrenosin gel phase. In both the solid and gel phases natural cerebroside exhibits a composite amide I mode. The disruptive effects on cerebroside chain packing and headgroup orientation arising from mixing with dimyristoyl phosphatidylcholine are examined. Vibrational data for cerebroside are also compared to those for ceramide, sphingosine, and distearoyl phosphatidylcholine structures. Spectral interpretations are discussed in terms of calorimetric and X-ray structural data.

Accessibility of galactosyl ceramides to probe reagents in central nervous system myelin

The suitability of isolated central nerve myelin preparations for probe labelling studies was assessed and the accessibility of galactosyl ceramides in myelin to galactose oxidase and sodium periodate was determined. Isolated myelin preparations present a uniform external membrane surface to added probes because lamellae in the myelin sheath separate at their external apposition surfaces exclusively during isolation. The cytoplasmic apposition remains intact in isolated myelin. Cationised ferritin can gain access along external apposition regions of inner lamellae in multilamellar fragments of isolated myelin, indicating that proteins and lipids on the external membrane surface will be accessible to probes. Over 50% of the total galactosyl ceramides of myelin are accessible to galactose oxidase attack; hydroxy fatty acid- and nonhydroxy fatty acid-containing cerebrosides are equally attacked. Sodium periodate attacks over 90% of the galactosyl ceramides in isolated myelin at 20 degrees C and electron micrographs of the periodate-treated myelin reveal changes at the external apposition only. Galactosyl ceramides in vesicles of myelin lipid vesicles are not so readily attacked by periodate. The disposition of galactosyl ceramides in the myelin lamellae is discussed.

Preliminary results of J-resolved, two-dimensional 1H-NMR studies on glycosphingolipids

Homonuclear J-resolved two-dimensional spectroscopy has been applied to the simplest glycosphingolipid, glycosylceramide. In comparison with the conventional one-dimensional spectrum, the possible advantages and shortcomings of the two-dimensional method as applied to blood-group-active glycosphingolipids consisting of several saccharide units, have been pr esented. As an example, preliminary results on a more complex pentaosylceramide (IV3Gal-alpha-neolactotetraosylceramide) are discussed.

A comparison of the properties and bile salt specificities of galactosylceramide and lactosyl ceramide beta-galactosidase activities in human leucocytes and fibroblasts

The properties and bile salt specificities of galactosylceramide and lactosylceramide beta-galactosidase activities (GC and LC-beta-galactosidases) of human leucocytes and fibroblasts were compared. A number of differences were observed. Under the standard assay conditions the former activity was more sensitive to Zn2+ and Triton-X100. Glycocholate and cholate were more active stimulators of the GC-beta-galactosidase than the more frequently used taurocholate which was the most effective stimulator of LC-beta-galactosidase activity. It is postulated that some of the apparent differences in the properties of GC- and LC-beta-galactosidase activities may be attributed to the different micellar properties of the lipid substrates. Experiments with fibroblasts from patients with Krabbe's disease confirmed an almost total absence of GC-beta-galactosidase whichever bile acid was employed. Residual LC-beta-galactosidase activity detected in these cells was much higher ranging from 13% of the lowest measured value when measured with taurocholate to approximately normal values with glycocholate. Fibroblasts obtained from patients with GM1-gangliosidosis displayed close to normal GC and LC-beta-galactosidase activity under our experimental conditions. The data suggest that diagnoses of Krabbe's disease should be performed with galactosylceramide rather than lactosylceramide as substrate.

Lipid domain formation and ligand-induced lymphocyte membrane changes

Spectral parameters of spin-labelled phosphatidylcholine, ceramide and cerebroside in the plasma membranes of human blood lymphocytes were measured before and after treatment with various ligands, which included concanavalin-A and phytohemagglutinin. It was found that ligand treatment led to a significant decrease in order of the hydrocarbon chains of the phospholipids. This was accompanied by a clustering of the labelled spingolipids, as estimated by spin-spin interaction, and an increase in the order of their hydrocarbon chains. In the untreated cells the cerebroside fatty acid chain was more ordered than that of the phosphatidylcholine. It was considered that the decrease in phospholipid order was brought about by the sequestration of the more rigid sphingolipids into the patches and caps formed by receptor-ligand complexes. The significance of these changes in lipid distribution and ordering is discussed in relation to the activation of membrane enzyme systems by mitogenic ligands.

Sodium ion diffusion through liposome membranes containing cerebroside

Na+ efflux from liposomes (small unilamellar vesicles, SUV) of various compositions was studied, using 22Na+ and 3H-labelled stachyose in simultaneous dual isotope measurements, stachyose being used as a measure of liposome disintegration. Dialysis was utilised to separate liposomes from extra-liposomal activity. Liposomes were made from egg lecithin and sphingomyelin and from mixtures of egg lecithin, sphingomyelin, cerebroside, sulphatide and cholesterol. All mixtures produced more leaky and less stable SUVs than pure lecithin and pure sphingomyelin. The incorporation of cerebroside is significantly smaller than that of the phospholipids including sphingomyelin. It was found that membranes containing cerebroside had a significantly higher Na+ permeability than membranes without cerebroside.

High resolution nuclear magnetic resonance spectroscopy of glycosphingolipids. I: 360 MHz 1H and 90.5 MHz 13C NMR analysis of galactosylceramides

The high resolution 1H and 13C nuclear magnetic resonance (NMR) spectra of galactosylceramides containing n-fatty acids and alpha-hydroxy fatty acids were recorded in dimethylsulfoxide solution with and without addition of D2O. From the coupling constants of the sugar ring protons, a 4C1 conformation can be deduced. In contrast to the conformation in aqueous solution, the C6 hydroxymethylene group is freely rotating around the C6--C5 bond. In the ceramide residue all signals produced by protons linked to carbons bearing electronegative substituents could be attributed. The large difference in coupling constants of the methylene protons of C1' to the C2' methine proton of the sphingosine indicates a restricted rotation around the C1'--C2' bond. The assignments of the hydroxy and amino protons follow from the decoupling of the corresponding methine protons.

Deuterium NMR studies of cerebroside-phospholipid bilayers

2H-NMR was used to probe the interaction of non-hydroxy fatty acid cerebroside and 2-hydroxy fatty acid cerebroside with the polar head group and with the acyl chains of dipalmitoylphosphatidylcholine in unsonicated bilayers. It is shown that the interior of the bilayer exhibits uniformly increasing orientational order as the concentration of both types of cerebroside increases, whereas the surface of the bilayer, as reflected by the head group motion, becomes disordered. The extent of the disorder at the surface is dependent upon the type and concentration of the cerebroside. These results are discussed in terms of hydrogen-bonding interactions.

Structure of cerebrosides. II. Small angle X-ray diffraction study of cerasine

Cerasine having a molecular weight of 800 differs chemically from phrenosine only in the hydroxyl group attached to the fatty acid tail which is replaced by a hydrogen atom. Nevertheless, remarkable differences between both cerebrosides are detected in the lamellae periodicities. In the range of 23--66 degrees C just one single (instead of two) structure with a similar subcell to the triclinic one component of phrenosine detected. Between 66 and 87 degrees C three new components (instead of one in phrenosine) appear. Two of the structures are similar to the two phrenosine-components at low temperature and the tilt angles of their chains with respect to the basal planes can explain the stabilizing capacity of the 201 and 301 netplanes of the paraffin-like subcells respectively. These lattice planes are parallely aligned to the surfaces of the lamellae. The long period of 58 A of component II cannot be explained in such a way. This period persists up to 105 degrees C and coexists from 87 degrees C with a new component showing a 40 A-periodicity, which cannot either be explained in the above manner. Paracrystalline distortions of the arrangement of the bilayers can be justified by orientational disorder of the galactose heads.