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

Decay-accelerating factor (DAF) is a C regulatory protein which functions in membranes to inhibit autologous C activation on cell surfaces. A liposome model was used to study the mechanism of DAF action and examine the effects of membrane-bound glycophorin and LPS on the regulatory activity of DAF. Liposomes were incubated in MgEGTA-treated human serum and activation of the alternative pathway measured by C3b binding. Liposomes composed of phosphatidylcholine, phosphatidylethanolamine, and cholesterol activated the alternative pathway in proportion to their content of PE. Incorporation of 10(-7) mol/mol phospholipid of either human E or HeLa cell-derived DAF inhibited C activation by liposomes containing 40% phosphatidylethanolamine by 50%, an efficiency comparable to that observed in intact E. HeLa DAF that had been treated with phosphatidylinositol-specific phospholipase C to remove its glycolipid anchor had no effect on C activation by liposomes at concentrations as high as 10(-5) mol/mol phospholipid. Incorporation of DAF into liposomes prepared with bound C3b inhibited the deposition of additional C3b by C3bBbP. However, the incorporated DAF increased the amount of Bb generated from B in the presence of D indicating that accelerated decay of the convertase was the primary effect of DAF. Similarly, treatment of intact human E with anti-DAF decreased the amount of Bb generated by the alternative pathway convertase. To study the effects of other membrane components on DAF activity, liposomes were prepared with purified human glycophorin A or LPS. In glycophorin liposomes the presence of PE was required to activate the alternative pathway and DAF inhibited this activation. In contrast, LPS liposomes bound C3b independently of PE and the incorporation of DAF had no effect. These results demonstrate that within a membrane, DAF's inhibitory activity on the alternative pathway C3 convertase is mediated independently of other membrane proteins, that in this model the major activity of DAF is to accelerate convertase decay, and that the presence of other membrane molecules that may serve as C3 acceptors can circumvent DAF function.
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PMID:The influence of membrane components on regulation of alternative pathway activation by decay-accelerating factor. 170 Sep 97

Membrane-associated decay accelerating factor (DAF) of human erythrocytes (Ehu) was analyzed for a C-terminal glycolipid anchoring structure. Automated amino acid analysis of DAF following reductive radiomethylation revealed ethanolamine and glucosamine residues in proportions identical with those present in the Ehu acetylcholinesterase (AChE) anchor. Cleavage of radiomethylated 70-kilodalton (kDa) DAF with papain released the labeled ethanolamine and glucosamine and generated 61- and 55-kDa DAF products that retained all labeled Lys and labeled N-terminal Asp. Incubation of intact Ehu with phosphatidylinositol-specific phospholipase C (PI-PLC), which cleaves the anchors in trypanosome membrane form variant surface glycoproteins (mfVSGs) and murine thymocyte Thy-1 antigen, released 15% of the cell-associated DAF antigen. The released 67-kDa PI-PLC DAF derivative retained its ability to decay the classical C3 convertase C4b2a but was unable to membrane-incorporate and displayed physicochemical properties similar to urine DAF, a hydrophilic DAF form that can be isolated from urine. Nitrous acid deamination cleavage of Ehu DAF at glucosamine following labeling with the lipophilic photoreagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID) released the [125I]TID label in a parallel fashion as from [125I]TID-labeled AChE. Biosynthetic labeling of HeLa cells with [3H]ethanolamine resulted in rapid 3H incorporation into both 48-kDa pro-DAF and 72-kDa mature epithelial cell DAF. Our findings indicate that DAF and AChE are anchored in Ehu by the same or a similar glycolipid structure and that, like VSGs, this structure is incorporated into DAF early in DAF biosynthesis prior to processing of pro-DAF in the Golgi.
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PMID:Decay accelerating factor of complement is anchored to cells by a C-terminal glycolipid. 243 21

A membrane protein of MW 60,000 was purified from mouse erythrocytes. This protein inhibits generation of mouse complement C3/C5 convertases on antibody-sensitized rabbit erythrocytes, in a haemolytic assay system using guinea-pig serum diluted in EDTA as the source of C3 to C9. This protein also has the capacity to accelerate the decay of human C3 convertase of the classical complement pathway. Antibody to this membrane protein also reacted with peripheral blood mononuclear cells and spleen cells, as observed by fluorescent flow cytometry analysis. Since the reactivity of these cells to the antibody was reduced by treatment with phosphatidyl inositol-specific phospholipase C (PIPLC), it is suggested that the protein is attached to the membrane via a glycophospholipid anchor. Based on these results, we conclude that this membrane protein is a murine homologue of human decay-accelerating factor (DAF).
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PMID:Murine membrane inhibitor of complement which accelerates decay of human C3 convertase. 248 41

Intact Haemophilus pleuropneumoniae cells (strain Shope 1, serotype 1), highly purified lipopolysaccharide (LPS) obtained from this strain of H pleuropneumoniae, as well as from Escherichia coli O111:B4, filter-sterilized H pleuropneumoniae cell-free culture supernatant fluid, and heat-inactivated supernatant fluid were given intranasally to CF1 mice and intratracheally to pigs. Pulmonary lesions induced by H pleuropneumoniae in mice were similar to those induced by H pleuropneumoniae in pigs. Histologically, lungs of mice and pigs killed 1 or 2 days after inoculation with 200 micrograms of highly purified H pleuropneumoniae LPS had lesions similar to one another and were similar to those in mice and pigs given intact H pleuropneumoniae, except that little or no necrosis or hemorrhage was observed. In mice killed 1 or 2 days after inoculation of 200 micrograms of E coli O111:B4 LPS, pulmonary lesions were similar to those in mice given H pleuropneumoniae LPS. Pulmonary lesions in mice given cell-free culture supernatant fluid obtained from a midlog-phase growth culture of H pleuropneumoniae cultivated in a chemically defined medium were severe and consisted of neutrophil infiltration and extensive necrosis. In mice, the heat-inactivated supernatant fluid produced mild lesions that consisted of foci of neutrophil aggregation and no necrosis. Extensive necrosis observed in lesions caused by cell-free culture supernatant fluid could be attributed to the action of a heat-labile component, perhaps by the extracellular heat-labile hemolysin produced by H pleuropneumoniae cultivated in chemically defined medium. A LPS endotoxin and a heat-labile factor may be involved in the pulmonary lesion development in the acute phase of porcine Haemophilus pleuropneumonia.
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PMID:Role of haemophilus pleuropneumoniae lipopolysaccharide endotoxin in the pathogenesis of porcine Haemophilus pleuropneumonia. 359 76

MCA44 is a mAb with the capacity to sensitize neuraminidase-treated guinea pig E for hemolysis by homologous guinea pig C, and the Fab fragments of this mAb could also sensitize guinea pig E interfering with the function of a membrane inhibitor of C on guinea pig E. Using an immunosorbent column to which MCA44 was coupled, the antigenic molecule termed 44Ag was purified from the glycoprotein fraction extracted from E membranes. C intermediate sheep E treated with guinea pig C1 and C4 after sensitization with Ab (EAC14b cells) lost the ability to generate C3 convertase with C2 after incubation with 44Ag. Treatment of guinea pig E and PBL with phosphatidyl-inositol specific phospholipase C (PIPLC) partially removed 44Ag, as determined by flow cytometric analysis after immunofluorescence staining with MCA44. However, 125I-labeled 44Ag adsorbed to human E was efficiently removed by PIPLC treatment with a slight reduction in M(r). The 44Ag purified on an immunosorbent column showed three bands on SDS-PAGE. However, partial N-terminal amino acid sequences of the 55-kDa, 70-kDa, and 88-kDa bands under nonreducing conditions were identical and the sequence was 55% homologous to the N-terminal sequence of human decay accelerating factor (CD55). Intracutaneous administration of MCA44 or its F(ab')2 fragment resulted in increased capillary permeability, even after 3 days, as determined by the appearance of Evans blue spots after i.v. administration of the dye. Because control Abs including anti-class I-MHC did not cause such increased capillary permeability, the increase in permeability caused by MCA44 was likely induced by blocking the function of 44Ag in vivo, indicating a crucial role for these molecules in preventing over-activation of C at the site.
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PMID:A monoclonal antibody that blocks the complement regulatory activity of guinea pig erythrocytes and characterization of the antigen involved as guinea pig decay-accelerating factor. 753 42

A developmentally regulated, 160-kDa trypomastigote surface glycoprotein was previously shown to bind the third component of complement and to inhibit activation of the alternative complement pathway, thus providing the parasites a means of avoiding the lytic effects of complement. We now show that this complement regulatory protein (CRP) binds human C4b, a component of the classical pathway C3 convertase, and may therefore also act to restrict classical complement activation. Characterization of the extent of carbohydrate modification of the protein revealed extensive N-linked glycosylation and no apparent O-linked sugars. The CRP purified from parasites treated with an inhibitor of N-linked glycosylation exhibited a decreased binding affinity for C3b compared with that of the fully glycosylated protein. We have previously shown that the protein was anchored to the membrane via a glycosyl phosphatidylinositol linkage and was spontaneously shed from the parasite surface. The spontaneous release of CRP from the parasite surface may augment the protection of the parasites from complement-mediated lysis by the removal of complement-CRP complexes. The majority of the shed CRP had an apparent molecular mass of 160 kDa and lacked the glycolipid anchor, whereas the membrane form was recovered with the glycolipid anchor attached and had an apparent molecular mass of 185 kDa. Both the membrane form (185 kDa) and the soluble form (160 kDa) retained binding affinity for C3b. Evidence is presented to indicate that the conversion of the 185-kDa membrane form to the 160-kDa form is the result of cleavage by an endogenous phospholipase C.
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PMID:Biochemical analysis of the membrane and soluble forms of the complement regulatory protein of Trypanosoma cruzi. 826 33

The enzyme activities of listeriolysin O (LLO), phosphatidylinositol-specific phospholipase C (PI-PLC), catalase (CA), and superoxide dismutase (SOD) from Listeria monocytogenes SLCC 5764 were examined after heat treatment, growth at elevated temperatures, and anaerobic growth. Growth at elevated temperatures may influence virulence as expressed by virulence enzyme activity. The enzymes were heated for 0 and 10 min at temperatures ranging from 40 to 100 degrees C. The production of LLO was examined when the bacterium was grown at elevated temperatures, and the production of LLO, CA, and SOD were examined after anaerobic growth. LLO was the most heat-labile factor, losing almost all activity when heated above 50 degrees C. CA was more heat stable, showing no decrease in activity until it was heated at 55 degrees C. The PI-PLC enzyme was most heat resistant: the activity decreased between 40 and 50 degrees C and continued to decrease when heated between 65 and 100 degrees C. When L. monocytogenes was grown at elevated temperatures, it produced less LLO than when grown at the optimum growth temperature of 37 degrees C. When the organism was grown under anaerobic conditions, the levels of CA and LLO decreased, while the SOD level remained unchanged.
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PMID:Heat stability of virulence-associated enzymes from Listeria monocytogenes SLCC 5764. 967 77