Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The identification of free glycoinositol phospholipids (GPIs) following biosynthetic labeling with [3H]glucosamine in cultured cells has been reported by several laboratories. We applied this procedure to two of the cell types used in these studies, H4IIE hepatoma cells and isolated hepatocytes, but were unable to detect a [3H]glucosamine-containing lipid that met any of the criteria for GPIs, including sensitivity to phosphatidylinositol-specific phospholipase C (PIPLC) or GPI-specific phospholipase D. Part of the difficulty in radiolabeling a GPI by this procedure was the rapid metabolic conversion of [3H]glucosamine to galactosamine and neutral or anionic derivatives. A PIPLC-sensitive radiolabeled lipid was detected only after 16 h of labeling. The water-soluble fragments released from this lipid by PIPLC corresponded largely to myo-inositol 1,2-cyclic phosphate and myo-inositol 1-phosphate, products expected from PIPLC cleavage of phosphatidylinositol or lyso-phosphatidylinositol. In an alternative approach that we introduce here, free GPIs in lipid extracts from rat liver plasma membranes were labeled by reductive radiomethylation. This procedure, which radiomethylates primary and secondary amines, has been shown to label a glucosamine residue adjacent to inositol in all GPIs characterized to date. The labeled extracts were fractionated by two-dimensional thin-layer chromatography, and a cluster of polar labeled lipids were assigned as GPIs based upon the following observations. 1) They were cleaved by PIPLC, 2) after hydrolysis in 6 N HCl, both radiomethylated glucosamine and a glucosamine-inositol conjugate were identified by cation exchange chromatography, and 3) hydrolysis in 4 M trifluoroacetic acid generated a fragment consistent with glucosamine-inositol-phosphate. These results illustrate new criteria for the identification of GPIs. The labeled GPIs also contained radiomethylated ethanolamine, another component found in GPI anchors of proteins and in mature lipid precursors of GPI anchors, suggesting that the liver plasma membrane GPIs retained considerable structural homology to GPI anchors.
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PMID:Identification of glycoinositol phospholipids in rat liver by reductive radiomethylation of amines but not in H4IIE hepatoma cells or isolated hepatocytes by biosynthetic labeling with glucosamine. 132 29

In patients with malaria, the clinical manifestations of the disease are associated with the presence of high concentrations of tumour necrosis factor (TNF) in the serum. Blood-stage parasites of human and rodent malarial parasites release serologically related exoantigens which induce the production of TNF in vitro and in vivo and which can kill mice made hypersensitive to TNF by pretreatment with D-galactosamine. They also elicit the production of T-independent antibody, which blocks these effects. The capacity of the exoantigens to stimulate macrophages to secrete TNF does not require the presence of protein or carbohydrate, but is associated with a lipid whose activity can be abolished by treatment with phospholipase C. Treatments of the exoantigens which destroyed their activity in vitro also abrogated their immunogenicity and their toxicity for mice. No TNF-inducing activity could be detected in preparations of parasitized erythrocytes that was not associated with phospholipid, and the TNF-inducing properties of the malarial phospholipids are quite distinct from those of bacterial lipopolysaccharide. We conclude that release of potentially toxic phospholipids by parasites may be responsible for some of the pathology of malaria.
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PMID:Tumour necrosis factor induction by malaria exoantigens depends upon phospholipid. 153 89

Recent evidence suggests that insulin induces hydrolysis of phosphatidylinositol-glycan (PI-G) and releases inositol-glycan (IG) and diacylglycerol (DAG). These two mediators are speculated to mediate different insulin actions. In this study, we examined metabolic labeling of PI-G in BC3H-1 myocytes with known precursors of PI-G. PI-G was metabolically labeled with [3H]myo-inositol, [3H]glucosamine, [3H]galactose, [3H]glycerol, and [3H]myristic acid. The treatment of 3H-labeled PI-G with phosphatidylinositol-specific phospholipase C liberated [3H]myo-inositol, [3H]glucosamine, or [3H]galactosamine-labeled IgGs, and [3H]glycerol or [3H]myristic acid-labeled DAG. In BC3H-1 myocytes, insulin induced phosphodiesteratic hydrolysis of PI-G and stimulated generation of IGs and DAG. Released IGs were labeled with [3H]myo-inositol, [3H]glucosamine, and [3H]galactose. Released DAG was labeled with [3H] glycerol and [3H]myristic acid. The IG had a dose-dependent insulin-like activity on glucose oxidation and lipogenesis without affecting glucose transport in rat adipocytes. Insulin increased 3H radioactivities of IG and insulin-mimicking activities of IG. These results provided further evidence that hydrolysis of PI-G and generation of IGs and DAG might be early steps in some insulin actions.
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PMID:Insulin stimulates the generation of two putative insulin mediators, inositol-glycan and diacylglycerol in BC3H-1 myocytes. 202 33

The dependence of acyl-CoA synthetase on the lipid composition of rat liver plasma membranes has been investigated. For this purpose the composition of the membranes was modified by incorporation of different phospholipids in the presence of partially purified lipid transfer proteins. Another approach to the modification of the membrane phospholipid composition was treatment with exogenous phospholipase C and subsequent enrichment with different phospholipids. The experiments performed in vitro indicated that the presence of certain phospholipids such as phosphatidylnositol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylserine was essential for the activation of long chain fatty acids by acyl-CoA synthetase. However, some differences were observed when oleate and palmitate were used as substrates. Sphingomyelin was found to inhibit this activity especially when oleic acid served as substrate. In addition, we tried to modify in vivo the membrane lipid composition by treatment with D-galactosamine, which is known to induce acute hepatitis and cause biochemical and biophysical alterations in liver membranes. The results thus obtained confirmed the idea that the augmentation of the membrane lipids and especially of PI, PE and PG was accompanied by acyl-CoA synthetase activation. The presence of two different enzymes, activating the saturated and unsaturated fatty acids is discussed.
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PMID:Acyl-CoA synthetase activity depends on the phospholipid composition of rat liver plasma membranes. 772 15

The lipophosphoglycan (LPG)-like glycoconjugate expressed on the cell surface of Trypanosoma cruzi epimastigotes was isolated, purified, and partially characterized. The glycoconjugate migrated as a homogeneous band (42 kDa) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Matrix-assisted laser desorption ionization mass spectral analysis of the native molecule indicated the presence of two major components whose molecular masses were about 18.4 and 22.5 kDa. The LPG could be metabolically labeled with [3H]galactose, [3H]mannose, [14C]glucose, or [3H]palmitic acid. Monosaccharide compositional analysis of the LPG indicated that galactose, glucosamine, and sialic acid predominate over mannose, galactosamine, and inositol. A peptide associated with the LPG molecule contained about 40 amino acid residues per inositol and had threonine as the predominant amino acid. The LPG showed strong binding to Ricinus communis agglutinin-1 and Tritium vulgare wheat germ agglutinin, indicating the presence of terminal beta 1,4-linked galactosyl residue(s) and N-acetylglucosamine, respectively. Lectin binding studies also suggested the presence of a terminal beta-galactose and GlcNAc in the glycan-inositol lipid core of LPG. Virtually all of the sialic acids appeared to be located in the saccharide portion of the molecule. Treatment of the LPG with phosphatidylinositol-specific phospholipase C liberated an alkylacylglycerol. Structural analysis of the alkylacylglycerol and its acidic methanolysis products by gas-liquid chromatography/mass spectrometry indicated that the glycerol substituents were primarily the C16 1-alkyl group and C16 2-acyl group. The ratio of inositol to 1-O-alkyl-2-O-acylglycerol was 1:1. Treatment of the glycoconjugate with nitrous acid released a major phospholipid product that migrated close to the phosphatidylinositol standard on thin layer chromatography. This result implied that phosphatidylinositol was glycosidically linked to the nonacetylated amino sugar. Furthermore, the LPG was found to contain phosphate and was labile to mild acid hydrolysis, strongly suggesting that the intact molecule is related to Leishmania LPG. The most striking and unique feature of T. cruzi LPG is the presence of large amounts of glucosamine and sialic acid as well as galactosamine. These results indicate that the glycoconjugate expressed on the T. cruzi cell surface is a new type of LPG-like molecule anchored on the cell surface via an alkylacylphosphatidylinositol.
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PMID:Expression of a novel cell surface lipophosphoglycan-like glycoconjugate in Trypanosoma cruzi epimastigotes. 807 17

The precise mechanism by which insulin elicits its effects remains to be fully determined. A glycophospholipid, isolated from H35 cells, has been proposed as a possible precursor for an insulin-generated second messenger that mediates the intracellular effects of insulin. This glycolipid contains a hexosamine moiety, inositol, galactose and palmitate. We have isolated a glycolipid from cultured rat hepatocytes that exhibits chromatographic and radiolabelling characteristics similar to this proposed precursor. The glycolipid can be radiolabelled with glucosamine, galactosamine, galactose and palmitate, but not myristate or myoinositol. Incorporation of radiolabel into this glycolipid was insensitive to the presence of either insulin (10(-7) M) or phosphatidylinositol-specific phospholipase C (PI-PLC) in the culture medium. The cultured hepatocytes used exhibited normal insulin responses with respect to glycogen turnover and gene expression. Treatment of partially purified glycolipid with either PI-PLC or nitrous acid did not result in the generation of an aqueous soluble phosphooligosaccharide indicating that the glycolipid was not cleaved by either agent. This is in contrast to the reported cleavage of the glycolipids found in H35 hepatoma and lymphocytes. These results question the role of the putative phosphooligosaccharide mediator in the intracellular transduction system activated by insulin.
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PMID:Glycolipids isolated from cultured rat hepatocytes: analysis of their role in insulin signal transduction. 838 92

Lipophosphoglycan-like glycoconjugates were isolated, purified and partially characterized from Tritrichomonas foetus and Trichomonas vaginalis. Cell surface radiolabeling of both trichomonads by the galactose oxidase/NaB[3H]4 technique indicated that the glycoconjugate was located on the cell surface of the parasites. The glycoconjugates were extracted from the delipidated residue fraction with the solvent, water/ethanol/diethylether/pyridine/NH4OH (15:15:5:1:0.017) and were purified to homogeneity by Sepharose CL-4B followed by octyl-Sepharose chromatography and methanol precipitation. The glycoconjugates migrated as broad bands upon SDS-PAGE. The T. foetus glycoconjugate contained large amounts of fucose along with some mannose, galactose, glucosamine and glucose and trace amounts of galactosamine and inositol. The T. vaginalis glycoconjugate appeared to contain large amounts of glucosamine and galactose along with some glucose, mannose and traces of galactosamine and inositol. The surface-labeled glycoconjugates from both parasites was found to be deaminated with nitrous acid and susceptible to phosphatidylinositol-specific phospholipase C, indicating the presence of a phospholipid anchor. Furthermore, these glycoconjugate were found to contain phosphate and were labile to hydrolysis by mild acid, strongly suggesting that the intact molecule is related to Leishmania lipophosphoglycans (LPG). The most striking and the unique features of these glycoconjugate molecules are the presence of large amounts of fucose in T. foetus and glucosamine in T. vaginalis along with the presence of galactosamine in both parasites. These results indicate that these glycoconjugates are new types of LPG-like molecules expressed on the trichomonad cell surface and are structurally distinct from Leishmania LPG.
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PMID:Lipophosphoglycan-like glycoconjugate of Tritrichomonas foetus and Trichomonas vaginalis. 843 19

In the present investigation, a hCG sensitive glycosyl-phosphatidylinositol (GPI) was isolated from cultured rat granulosa cells obtained from the ovaries of diethylstilbestrol (DES) implanted immature rats. The inositol-phosphoglycan (IPG) moiety of the GPI-lipid contains galactose, glucosamine, and myoinositol as demonstrated by metabolic labelling of granulosa cells for different time periods (5-96 h) with [3H]galactose, [3H]glucosamine, or [3H]myoinositol and treatment of the purified [3H]GPI with phosphatidylinositol-specific phospholipase C. Labelling equilibrium of the GPI-lipid was achieved after 24 h ([3H]galactose and [3H]myoinositol) or 72 h ([3H]glucosamine) incubation, whereas incorporation of other labelled carbohydrates tested ([3H]galactosamine, [3H]mannose, and [3H]sorbitol) was negligible throughout the time period studied. The glucosamine C-1 appears to be linked through a glycosidic bond to the myoinositol molecule of the IPG moiety as revealed by the generation of phosphatidylinositol (PtdIns) after nitrous acid deamination of dual labelled ([3H]glucosamine/[14C]palmitate or [3H]glucosamine/[14C]myristate) glycosyl-phosphatidylinositol. To investigate the fatty acid composition of the diacylglycerol (DAG) backbone of the GPI, granulosa cells were also labelled (5-72 hr) with [14C]linoleate, [3H]myristate, [3H]oleate, [3H]palmitate, or [3H]stearate and the radioactivity associated with the purified glycosyl-phosphatidylinositol determined. Incorporation of [3H]palmitate and [3H]myristate into the GPI-lipid peaked after 8 h and 24 h of labelling, respectively, and both fatty acids were partially released after PLA2 treatment of the dual labelled ([3H]glucosamine/[14C]palmitate or [3H]glucosamine/[14C]myristate) GPI. In parallel experiments no significant incorporation of labelled stearate, oleate, or linoleic acid into the DAG backbone of the glycosylphosphatidylinositol could be detected. Granulosa cells were also labelled with [3H]glucosamine in the presence of FSH (30 ng/ml), cholera toxin (1 microgram/ml), or the membrane permeable cAMP analog (but)2cAMP (1 mM). Time related increases in GPI-labelling were apparent after 48 h and reached a maximum level (3-, 5-, and 7-fold for FSH, CT, and (but)2cAMP, respectively) after 72 h in culture. In another set of experiments, granulosa cells were labelled for 72 h with [3H]glucosamine in the presence of (but)2cAMP (1 mM), TPA (10(-7) M), or combination thereof. The effect of treatment with the membrane permeable cAMP analog on GPI labelling was prevented in the presence of TPA, whereas no differences in [3H]GPI content could be observed in untreated granulosa cells or cells cultured in the presence of the protein kinase C-activating phorbol ester alone.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Follicle-stimulating hormone and human chorionic gonadotropin induced changes in granulosa cell glycosyl-phosphatidylinositol concentration. 848 20