Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study we describe the biochemical features of the Toxoplasma gondii tachyzoite surface glycoprotein, gp23, demonstrating that it is attached to the parasite membrane by a glycosyl-phosphatidyl inositol anchor. Gp23 was metabolically labeled with tritiated palmitate, myristate, ethanolamine, inositol, glucosamine, mannose and galactose, as expected for a GPI-anchor structure. Gp23 was released from the surface of living parasites after treatment with phosphatidylinositol-specific phospholipase C(PI-PLC) and the resulting water-soluble protein was immunoprecipitated with a monoclonal antibody specific for gp23. The GPI-core glycan was generated after aqueous-HF dephosphorylation followed by nitrous acid deamination and its carbohydrate structure was analyzed using selective exo- and endoglycosidase treatments. Finally, the phosphatidylinositol moiety of gp23 was characterized using PI-PLC and phospholipase A2 (PLA2) digestions. Our cumulative data suggest that gp23 of T gondii tachyzoites contains a modified GPI-backbone similar to the mammalian Thy-1 anchor, consisting of a conserved core structure (ethanolamine-PO4-6-Man alpha1-2-Man alpha1-6-Man alpha1-4-GlcN alpha1-6-PI) bearing beta-linked N-acetylgalactosamine residue(s).
...
PMID:Structural analysis of glycosyl-phosphatidylinositol membrane anchor of the Toxoplasma gondii tachyzoite surface glycoprotein gp23. 824 58

Plasmodium falciparum is the causative agent of malaria tropica in man. Biochemical studies were focused on the asexual, intraerythrocytic stages of P. falciparum, because of their role in the clinical phase of the disease and the possibility of propagation in a cell culture system. In this report, we describe the in-culture labeling of malarial glycolipids and the analysis of their hydrophilic moieties. They were identified as glycosylphosphatidylinositols (GPIs) by: 1) labeling with [3H]mannose, [3H]glucosamine, and [3H]ethanolamine and 2) sensitivity toward glycosylphosphatidylinositol-specific phospholipase D, phospholipase A2, and nitrous acid. Malarial GPIs are shown to be unaffected by treatment with phosphatidylinositol-specific phospholipase C, regardless of prior treatment with mild base commonly used for inositol deacylation. Two candidates for putative GPI-anchor precursors to malarial membrane proteins with the structures ethanolamine-phosphate-6(Man alpha 1-2)Man alpha 1-2Man alpha 1-6Man alpha 1-4 GlcN-PI (Pfg1 alpha) and ethanolamine-phosphate-6Man alpha 1-2Man alpha 1-6Man-alpha 1-4-GlcN-PI (Pfg1 beta) were identified.
...
PMID:Glycosylphosphatidylinositols synthesized by asexual erythrocytic stages of the malarial parasite, Plasmodium falciparum. Candidates for plasmodial glycosylphosphatidylinositol membrane anchor precursors and pathogenicity factors. 830 May 89

An inositol phosphoglycan that is the polar head group of a glycosyl phosphatidylinositol has been considered as a putative mediator of insulin action. To gain insight into the functions of this hormone during development, the relationships between insulin, insulin receptors, glycosyl phosphatidylinositol, and inositol phosphoglycan were studied. Glycosyl phosphatidylinositol was isolated and characterized in fetal liver as early as day 15 of intrauterine life. In isolated hepatocytes from fetal and adult rats labeled with [3H]glucosamine, [3H]galactose, or [3H]myo-inositol, these molecules were incorporated into glycosyl phosphatidylinositol. In hepatocytes labeled with [3H]glucosamine and then allowed to react with [1-14C]IAI, the [3H]glycosyl phosphatidylinositol was purified as the 14C-labeled amidinated lipid. Glycosyl phosphatidylinositol molecules from fetal and adult cells were sensitive to hydrolysis by a phosphatidylinositol-specific phospholipase C from B. cereus. The product of this hydrolysis inhibits the activity of a cAMP-dependent protein kinase, whereas this effect was abolished by nitrous acid deamination. In isolated hepatocytes from adult animals, an inverse correlation between extracellular insulin and the number of insulin receptors and the cellular content of glycosyl phosphatidylinositol was observed. However, in fetal hepatocytes insulin failed to reduce the glycosyl-phosphatidylinositol content when labeled either with [1-14C]isethionyl acetimidate or [3H]glucosamine, whereas insulin-like growth factor I produced a significant hydrolysis of glycosyl phosphatidylinositol. Fetal and adult hepatocytes were incubated with insulin or inositol phosphoglycan after which glycogen phosphorylase activities were determined. Inositol phosphoglycan mimicked the action of insulin on both forms of the enzyme from adult hepatocytes, whereas in fetal cells insulin did not change, and purified inositol phosphoglycan reduced the activities of glycogen phosphorylase. These findings suggest a dissociation between insulin receptor occupancy and the expected hormonal effects in fetal hepatocytes. This could be related to alterations at a postreceptor level.
...
PMID:Insulin does not induce the hydrolysis of a glycosyl phosphatidylinositol in rat fetal hepatocytes. 834 37

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.
...
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.
...
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)
...
PMID:Follicle-stimulating hormone and human chorionic gonadotropin induced changes in granulosa cell glycosyl-phosphatidylinositol concentration. 848 20

Leishmania donovani donovani amastigotes, isolated from spleens of infected hamsters or axenically cultured, and promastigotes were comparatively examined for the expression of lipophosphoglycans (LPG). Parasites were metabolically labeled with [32p]-phosphate, [3H]galactose, or [3H]mannose. Radiolabeled material was extracted with water/ethanol/diethylether/pyridine/NH40H and purified further by gel filtration and hydrophobic column chromatographies. These radiolabeled compounds were identified as phosphorylated lipid-containing glycoconjugates. Mild acid treatment resulted in degradation of the glycolipids into low-molecular-weight fragments. All glycolipids isolated were susceptible to nitrous acid and phosphatidylinositol-specific phospholipase C treatments, as has been reported for the L. donovani promastigote LPG. Moreover, glycoconjugates purified from the three Leishmania stocks were not susceptible to trypsin treatment. Acid hydrolysis of promastigote LPG resulted in a predominant [P04-6galactose(beta1,4)mannose(alpha)1] fragment. In contrast, the main radiolabeled anionic fragments isolated from splenic and axenic amastigotes differed from that of promastigotes, as evidenced by the elution profiles obtained by HPLC anion-exchange chromatography. These cumulative results indicate that lipophosphoglycan molecules, structurally distinct from the previously characterized LPG of the promastigote stage, are being expressed by L. donovani splenic and axenic amastigotes.
...
PMID:Isolation of lipophosphoglycans from Leishmania donovani amastigotes. 883 32

Two variant sublines of murine L1210 leukemia cells (L1210A and L1210JF) overexpress the cell surface folate receptor (FR). The membrane bound FR in L1210A cells exhibited significantly (up to 17-fold) greater relative affinities for (6S)-N5-methyltetrahydrofolate, (6S)-N5-formyltetrahydrofolate and methotrexate compared to the FR in L1210JF cells. Furthermore, receptor-mediated transport of [3H]-(6S)-N5-methyltetrahydrofolate was much more efficient in L1210A cells compared to L1210JF cells. When solubilized with Triton X-100, the ligand binding characteristics of FR from both sublines resembled those of the receptor associated with L1210 JF cell membranes. N-terminal amino acid sequence analysis as well as RT-PCR analysis of the entire coding region revealed a single species of FR in both cells, identical to murine FR-alpha. The FR in L1210JF cells was sensitive to phosphatidylinositol specific phospholipase C (PI-PLC) indicating the presence of a glycosyl-phosphatidylinositol (GPI) membrane anchor while the FR in L1210A cells was resistant to PI-PLC; however, the FR in L1210A cells was released from plasma membranes by nitrous acid, as expected for GPI and its PI-PLC resistant structural variants. Treatment of L1210A cell membranes with mild base rendered the protein PI-PLC sensitive as expected for GPI anchors acylated in the inositol ring and also decreased the affinities of the membrane associated FR for reduced folates. When the cDNA for murine FR-alpha was expressed in parental L1210 cells the protein was PI-PLC resistant but was sensitive to PI-PLC when the cDNA was expressed in human 293 fibroblasts. In L1210JF, L1210A, and parental L1210 cells, several cell surface proteins, including FR, incorporated [3H]ethanolamine, a component of the GPI membrane anchor; however, the labeled proteins were released by PI-PLC only in L1210JF cells. The above results preclude any peculiarity of the FR polypeptide in either L1210 subline as the basis for the observed differences in PI-PLC sensitivity and membrane-associated functions of FR. Partial deglycosylation of membrane associated FR from either cell with N-glycanase did not influence its ligand binding characteristics. The results of this study lead to the hypothesis that variant GPI structures may modulate the function of a protein by influencing its conformation/topography in the membrane. Such effects may be identified by their disappearance/reduction upon detergent solubilization or mild base treatment of the membrane.
...
PMID:Variant GPI structure in relation to membrane-associated functions of a murine folate receptor. 897 5

Glycosyl phosphatidylinositols have been implicated in insulin signaling through their action as precursors of second messenger molecules in peripheral tissues. In the present study, cultured rat astrocytes were used to investigate whether glycosyl phosphatidylinositol might be involved in the mechanism of insulin signal transduction in neural cells. A glycosyl phosphatidylinositol sensitive to hydrolysis by both phosphatidylinositol-specific phospholipase C and glycosyl phosphatidylinositol-specific phospholipase D and to nitrous acid deamination was purified. When astrocytes were exposed to 10 nM insulin, a rapid and significant reduction in the content of glycosyl phosphatidylinositol was observed within 1-2 min. In addition, an inverse concentration-dependent relationship between glycosyl phosphatidylinositol and diacylglycerol levels was found, suggesting a phospholipase C-mediated hydrolysis of glycosyl phosphatidylinositol in response to insulin. The effects of insulin were mediated through its own receptors and not through insulin-like growth factor (IGF)-I and/or IGF-II receptors, as demonstrated by affinity cross-linking studies. Also, the effects of 5 nM IGF-1 or 5 nM IGF-II on glycosyl phosphatidylinositol and diacylglycerol levels were different from those caused by insulin and were not essentially modified by pretreatment of the cells with either platelet-derived growth factor (PDGF) or epidermal growth factor (EGF). When cells were sequentially incubated with PDGF and EGF, a reduction in both glycosyl phosphatidylinositol and diacylglycerol contents was observed; the diacylglycerol but not the glycosyl phosphatidyl content was reversed after incubation with IGF-I, and especially with IGF-II, for 10 min. Despite the remarkable homology among insulin, IGF-I, and IGF-II, our results indicate that in astrocytes these compounds probably use different signal transduction pathways.
...
PMID:Insulin promotes the hydrolysis of a glycosyl phosphatidylinositol in cultured rat astroglial cells. 897 4

Insulin sensitive glycosylated phosphatidylinositol (GPI) from chick embryo fibroblasts was isolated and partially characterized. [(3)H]Ethanolamine was incorporated into lipids different from phosphatidylethanolamine, as shown by two sequential thin layer chromatographies (TLC) using an acidic solvent system followed by a basic solvent system. Other isotopes, myo-[(3)H]inositol, [(3)H]glucosamine, [(3)H]galactose, and [(3)H]palmitic acid were also incorporated into these lipids. These lipids were separated into two peaks on the second basic TLC, designated as peaks I and II from the origin. Insulin stimulation of cells caused a rapid breakdown of these two lipids. These two lipids were treated by nitrous acid and phosphatidylinositol-specific phospholipase C (PI-PLC). The radioactivity of peak I lipid was decreased by both treatments, and that of peak II lipid was also decreased by PI-PLC treatment but not significantly by nitrous acid treatment. Peak II lipid did not fulfill the criteria for GPI. Tritium released by the treatment of PI-PLC of peak I lipid was recovered in the aqueous phase. [(3)H]Ethanolamine-labeled peak I lipid was hydrolyzed by acid treatment and the hydrolysis products were analyzed by TLC and high performance liquid chromatography (HPLC). Tritium label was recovered as native label at the rate of 95%. [(3)H]Ethanolamine of peak I lipid was reductively methylated completely with formaldehyde and cyanoborohydride, as shown by HPLC analysis. The results indicate that peak I lipid contains primary ethanolamine as a glycan component and is insulin-sensitive free GPI.
...
PMID:Incorporation of ethanolamine into insulin-sensitive glycosylated phosphatidylinositol of chick embryo fibroblasts. 1108 35


<< Previous 1 2 3 4 5 6 7 Next >>

---