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PubMed1979

Conversion by rat brain preparation of lignoceric acid to ceramides and cerebrosides containing both alpha-hydroxy and nonhydroxy fatty acids. Effects of compounds which affect sphingolipid metabolism.

Three synthetic compounds which affect sphingolipid metabolism in vitro were examined for their effects on the synthesis in a rat brain system of nonhydroxyceramide, hydroxyceramide, nonhydroxycerebroside, and hydroxycerebroside from [1-14C]ignoceric acid. These compounds are N-octanoyl-D-threo-p-nitrophenylaminopropanediol (Compound I), N-(2,3-epoxydecanoyl)-norephedrine (Compound II), and N-decyl-N'-glucosylthiourea (Compound III). In the presence of up to 0.5 mM Compound I, only the hydroxyceramide fromation increased, while the synthesis of the other three lipids decreased. Compound II strongly inhibited the formation of all four lipids at all concentrations tested (0.1 to 1 mM). Compound III increased the synthesis of both ceramides approximately 2-fold at 1 mM, but the conversion of lignoceric acid to both cerebrosides remained relatively unchanged. Several significant conclusions from these observations are discussed.

Animals↗
PubMed1977

Synthesis of myelin glycosphingolipids (galactosylceramide and galactosyl(3-O-sulfate)ceramide (sulfatide)) by cloned cell lines derived from mouse neurotumors.

Clonal cell lines derived from both spontaneous and chemically induced rat and mouse brain tumors were screened for their ability to incorporate H232SO4 into galactosyl(3-O-sulfate)ceramide (sulfatide). High levels of 35SO4 incorporation into sulfatide were found only in two of the mouse cell lines studied (G26-20 and -24). Tumors produced by subcutaneous injection of these cell lines into C57BL/6 mice were also unique in that they contained high levels of both sulfatide and galactosylceramide. The synthesis of large amounts of sulfatide and galactosylceramide by a clonal cell line of neurological origin suggests that the original tumor was of oligodendrocyte or Schwann cell origin. In common with a large number of mouse and rat astrocyte cell strains and their derived tumors, these glial cells lacked the ability to synthesize gangliosides such as monosialotetraglycosylceramide and disialotetraglycosylceramide (as judged by analytical and [3H]GlcNH2 incorporation studies). This appears to be a unique characteristic of neuroblastoma-derived cell strains such as N18, NB2a, and NB41A.

Animals↗
PubMed1979

Consecutive analysis of sphingoglycolipids on the basis of sugar and ceramide moieties by high performance liquid chromatography.

A quantitative consecutive method was developed for analysis of sphingoglycolipids in biological materials by high performance liquid chromatography (HPLC). Crude lipid extracts were separated into neutral and acidic fractions on a DEAE-Sephadex column. Glycolipid fractions were obtained by acetylation and Florisil column chromatography, and the acetylated glycolipids were N-p-nitrobenzoylated by treatment with p-nitrobenzoyl chloride in pyridine at 60 degrees C for 6 h. Excess reagent and by-products were removed by solvent partition and gel filtration. The glycolipid derivatives were analyzed by their absorption at 254 nm on Zorbax SIL, a silica gel column, with a gradient of 0.5--7% isopropanol in hexane-chloroform (2 : 1, v/v) at a flow rate of 0.5 ml/min. The detector response was linear with up to 60 nmol of injected glycolipids. The practical lower limit of detection was about 50 pmol. The derivatives were separated on the basis of their sugar chains. Effluents corresponding to each peak were collected and analyzed further on the basis of their lipid portion on mu-Bondapak C18, a reversed phase column. This combined procedure was applied to the analysis of erythrocyte glycolipids. Samples containing as little as 20 micrograms of glycolipids could be analyzed by this method.

Animals↗
PubMed1979

The use of liposomes as acceptors for the assay of lipid glycosyltransferases from rat brain.

Preparation and characterization of sonicated vesicles of various lipid composition containing hydroxy and normal fatty acid ceramides are reported. Such vesicles have been successfully used for the first time as acceptors for the assays of lipid glycosyltransferases, UDP-galactose:ceramide galactosyltransferase and UDPglucose: ceramide glucosyltransferase. Stability of the vesicles and the optimal enzyme activities were the criteria used to select the final composition of the vesicles. The activities of the glycosyltransferases were dependent not only on the appropriate assay conditions but also on the type and source of the phospholipids used to form the liposomes. Ceramides containing normal fatty acids were incorporated into phosphatidylcholine vesicles in a molar ratio of 1 : 3.4 and used as the acceptor for the assay of UDPglucose:ceramide glucostyltransferase. For the assay UDP-galactose:ceramide galactosyltransferase, vesicles were prepared by sonication of bovine brain ethanolamine phospholipids, phosphatidylcholine and ceramide containing alpha-hydroxy fatty acids, in a molar ratio of 6 : 0.57 : 1. The size of the vesicles as determined by electron microscopic measurement ranged mostly between 200--500 A. The results obtained by selective labelling of the outer surface amino groups with the membrane-impermeable reagent, 2,4,6-trinitrobenzenesulfonic acid, indicated that the ethanolamine phospholipid-containing liposomes consisted of closed vesicles. After incubation with the appropriate cofactors and labelled sugar nucleotides, the radioactive reaction products were shown to cochromatograph with the authentic standards by thin-layer chromatography and autoradiography.

Animals↗
PubMed1975

Plasma glycosphingolipids in diabetics and normals.

In diabetic patients with hyperlipoproteinemia type IV the monohexosyl ceramide concentration in blood plasma is significantly elevated. This augmentation can be attributed to an increased monohexosyl ceramide content of the BLDL plasma fraction. In contrast, the di-, tri-, the tetrahexosyl ceramide levels remain within normal limits. In normolipidemic diabetics of comparable age, sex, and weight classes and of comparable metabolic control no elevations of glycolipid fractions could be found. However, patients with primary hyperlipoproteinemia type IV show an increase of monohexosyl ceramide concentrations in blood plasma. Therefore, the augmentation of monohexosyl ceramide levels in plasma of hyperlipidemic diabetic patients seems rather a metabolic consequence of hyperlipoproteinemia than of diabetes per se. A clearcut explantation for the monohexosyl ceramide elevations in the studied groups cannot be given at present time.

Blood Glucose↗
PubMed1979

Nature and mechanism of action of the CAMP protein of group B streptococci.

The extracellular product of group B streptococci responsible for the CAMP reaction was purified to near homogeneity. It is a relatively thermostable protein having a molecular weight of 23,500 and an isoelectric pH of 8.3. It was found that the CAMP reaction could be simulated by substituting [14C]glucose-containing liposomes prepared from sphingomyelin, cholesterol, and dicetyl phosphate for sheep erythrocytes. In the belief that the liposome system is a valid model, the mechanism of the CAMP reaction was further investigated by using liposomes in which N-acylsphingosine (ceramide) was substituted for sphingomyelin. In this system disruption of liposomes, as measured by release of trapped [14C]glucose, was effected by CAMP protein alone. As judged from thin-layer chromatography, CAMP protein caused no reduction in the amount of ceramide present in ceramide-containing liposomes, nor were split products demonstrable. However, binding of CAMP protein to ceramide-containing liposomes could be shown. It is inferred that in sheep erythrocytes CAMP protein reacts nonenzymatically with membrane ceramide formed by the prior action of staphylococcal sphingomyelinase and that binding of CAMP protein to ceramide disorganizes the lipid bilayer to an extent that results in cell lysis.

Amino Acids↗
PubMed1975

Characterization of a human intestinal fucolipid with blood group Lea activity.

A fucolipid that carried human blood group Lea activity was isolated from human small intestine. It contianed fucose, galactose, N-acetyl glucosamine, glucose, and ceramide in a molar ratio of 1:2:1:1:1. After periodate oxidation only 1 molecule of galactose and the N-acetylglucosamine remained. Permethylation of the lipid gave derivatives of a terminal fucose and galactose residue together with 2,4,6-tri-O-methylgalactose and 2,3,6-tri-O-methylglucose. After removal of fucose the lipid could be converted to a ceramide trihexoside with beta-galactosidase, and this, in turn, to ceramide lactoside by the action of beta-N-acetylhexosaminidase. Both enzymes converted the defucosylated derivative to a ceramide monohexoside. The methylated and the methylated and reduced derivatives of the intact lipid gave ions in mass spectrometry for a terminal hexose and deoxyhexose, a terminal trisaccharide of hexose, deoxyhexose and N-acetylhexosamine, and terminal tetra-and pentasaccharides. Ceramide fragments characteristic of hydroxy fatty acids with 16, 22, 23, and 24 carbons were found together with those of phytospingosine as the major long chain base. On the basis of these results and the immunologic activity of the fucolipid, the following structure is proposed: betaGal (1 leads to 3)betaGlcNAc (1 leads to 3)betaGal (1 leads to 4)Glc-ceramide alphaFuc (1 leads to 4).

Acetylglucosamine↗
PubMed1977

Substrate specificities of the two genetically distinct human brain beta-galactosidases.

The two human brain beta-galactosidases were solubilized and fractionated by Sephadex G-200 gel filtration, free from each other. Substrate specificities of the two enzymes were examined for galactosylceramide, lactosyl-[N-stearoyl]ceramide, lactosyl-[N-lignoceroyl]ceramide, galactosyl-N-acetylgalactosaminyl-[N-stearoyl]ceramide, lactosyl-[N-lignoceroyl]ceramide, galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]galactosyl-glucosylceramide (GMI-ganglioside), galactosyl-N-acetylgalactosaminyl-galactosyl-glucosylceramide (asialo GM1-ganglioside), and 4-methylumbelliferyl beta-galactoside. Under appropriately optimized conditions, either of the two beta-galactosidases could hydrolyze all of the substrates, although with widely varying rates. Relative specific activities of galactosylceramide beta-galactosidase toward galactosylceramide, lactosyl-[N-steroyl]ceramide, lactosyl-[N-lignoceroyl]ceramide. GM1-ganglioside, asialo GM1-ganglioside, and 4-methylumbelliferyl beta-galactoside were 100, 510, 250, 39, 41 and 120, respectively. Relative specific activities of GM1-ganglioside beta-galactosidase toward the same series of the substrates were 0.3, 78, 19, 100, 150 and 240; However, the optimal assay conditions for any given natural substrate were sufficiently different for each beta-galactosidase so that diagnostic assays for the two genetic diseases due to beta-galactosidase deficiencies could be carried out in whole tissues. Since the relative distribution of the two enzymes vary greatly in different tissues, contributions by the two enzymes to degradation of the natural glycosphingolipids in vivo may well vary in different organs. These findings may have an important bearing on the biochemical pathogenesis of these genetic disorders.

Adult↗