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

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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)

Decay-accelerating factor (DAF) is an integral membrane protein that inhibits amplification of the complement cascade on the cell surface. We and other investigators have shown that DAF is part of a newly characterized family of proteins that are anchored to the cell membrane by phosphatidylinositol (PI). The group includes the variant surface glycoprotein (VSG) of African trypanosomes, the p63 protein of Leishmania, acetylcholinesterase (AChE), alkaline phosphatase, Thy-1, 5'-nucleotidase, and RT6.2--an alloantigen from rat T cells. The structure of the membrane anchor has been best characterized for VSG, but chemical studies of the membrane anchors of AChE and Thy-1 suggest that similar glycolipid moieties anchor these proteins to the cell surface. In the VSG, the membrane anchor consists of an ethanolamine linked covalently to an oligosaccharide and glucosamine; the entire complex is anchored to the cell membrane by PI. Immunologically, this glycolipid defines an epitope, the cross-reacting determinant (CRD), that is only revealed after removal of the diacyl glycerol anchor by a phospholipase C. By Western blotting, we show here that DAF-S (DAF released from the membrane by PI-specific phospholipase C [PIPLC]) also contains CRD. Using a newly developed immunoradiometric assay (IRMA) in which the solid-phase capturing antibody is a monoclonal antibody to DAF and the second antibody is anti-CRD, we have been able to quantitate DAF-S. By IRMA, we show that the reaction between anti-CRD and DAF-S is specific, since the binding is competitively inhibited only by the soluble form of the VSG. These observations further support the concept that the glycolipid anchors of this new family of proteins have similar structures. DAF is also found as a soluble protein in various tissue fluids as well as in Hela cell supernatants. No evidence for the presence of the CRD epitope was found on these proteins, suggesting that these forms of DAF are not released from the surface of cells by endogenous phospholipases.
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PMID:Decay-accelerating factor (DAF) shares a common carbohydrate determinant with the variant surface glycoprotein (VSG) of the African Trypanosoma brucei. 243 27

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

This review seeks to assemble recent discoveries about insulin receptor/kinase, guanine nucleotide-binding proteins, phosphatidyl inositol metabolism, and protein phosphatases to provide a mechanistic pathway by which insulin would alter carbohydrate and fat metabolism. It proposes a hypothetical chain of events that leads from the insulin receptor to protein phosphatase-1. The sequence starts with insulin binding to its receptor, activating the intrinsic receptor/kinase activity. The insulin receptor phosphorylates a guanine nucleotide-binding protein, which activates a particular phospholipase C. This in turn stimulates the production of two lipid-derived messengers: inositol-phospho-glucosamine and diacylglycerol. These messengers trigger the effects of insulin. The diacylglycerol produced by insulin is thought to be analogous to the diacylglycerol produced by alpha-adrenergic stimulation, which activates protein kinase C. Activation of this kinase could account for increases in phosphorylation of certain proteins. The inositol-phospho-glucosamine is the cytosolic messenger for insulin. One of the enzymes activated by insulin is protein phosphatase type-1. It is known that the phosphatase decreases phosphorylation of certain target enzymes. In response to insulin, activation of protein phosphatase type-1 occurs with a stable conformational change that may involve rearrangement of disulfide bonds. Rearrangement is either directly in response to the cytosolic messenger or is catalyzed by an isomerase activated by the insulin messenger. Ultimately, protein phosphatase type-1 and/or the disulfide isomerase may together mediate the pleiotropic effects of insulin on carbohydrate and fat metabolism.
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PMID:Proposal for a pathway to mediate the metabolic effects of insulin. 283 73

The glycoinositol phospholipid membrane anchor of human erythrocyte acetylcholinesterase (EC 3.1.1.7) contains a novel inositol phospholipid which in this and the accompanying paper (Roberts, W.L., Santikarn, S., Reinhold, V.N., and Rosenberry, T.L. (1988) J. Biol. Chem 263, 18776-18784) is shown to be a plasmanylinositol that is palmitoylated on the inositol ring. The inositol phospholipid was radiolabeled with the photoactivated reagent 3-(trifluoromethyl)-3-(m-[125I] iodophenyl)diazirine and characterized by various chemical and enzymatic cleavage procedures whose products were analyzed by thin layer chromatography and autoradiography or gas chromatography. Acidic methanolysis of human erythrocyte acetylcholinesterase (Ehu AChE) revealed 18:0 and 18:1 alkylglycerols (0.55 and 0.20 mol/mol AChE, respectively). Acetolysis was shown by TLC to release alkylacylglycerol acetates from Ehu AChE. Analysis by gas chromatography revealed that 83% of the alkylacylglycerol acetates contained an 18:0 or 18:1 1-alkyl group and a 22:4 (n - 6), 22:5 (n - 3), or 22:6 (n - 3) 2-acyl group. The inositol phospholipid is linked to the anchor by a glucosamine in glycosidic linkage, and deamination with nitrous acid cleaved the glycosidic linkage and released the phospholipid. The deamination and acetolysis products from Ehu AChE were purified by high performance liquid chromatography, and fatty acid analysis following acidic methanolysis of the purified products revealed that 2 fatty acid residues were associated with the deamination product and only one with the alkylacylglycerol acetolysis product. The other fatty acid residue was primarily palmitate and was indicated to be in ester linkage to an inositol hydroxyl(s). This linkage was shown to be responsible for the resistance of the inositol phospholipid to cleavage by Staphylococcus aureus phosphatidylinositol-specific phospholipase. Deacylation of the inositol phospholipid deamination product by treatment with base removed this palmitoyl group and facilitated release of alkyl- and alkylacylglycerol species by phosphatidylinositol-specific phospholipase C with concomitant formation of inositol 1-phosphate. In contrast, digestion of Ehu AChE with a recently reported anchor-specific phospholipase D resulted in release of plasmanic acids from the intact palmitoylated plasmanylinositol.
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PMID:Lipid analysis of the glycoinositol phospholipid membrane anchor of human erythrocyte acetylcholinesterase. Palmitoylation of inositol results in resistance to phosphatidylinositol-specific phospholipase C. 284 6

The glycoinositol phospholipid membrane anchor of human erythrocyte acetylcholinesterase (EC 3.1.1.7) is composed of a glycan linked through a glucosamine residue to an inositol phospholipid that is resistant to the action of phosphatidylinositol-specific phospholipase C. Deamination cleavage of the glucosamine with nitrous acid released the inositol phospholipid which was purified by high performance liquid chromatography. Analysis by fast atom bombardment mass spectrometry with negative ion monitoring and by the complementary technique of collision-induced dissociation revealed molecular and daughter ions that indicated a plasmanylinositol with a palmitoyl group on an inositol hydroxyl. The intact membrane anchor was released from reductively methylated human erythrocyte acetylcholinesterase by proteolysis with papain or Pronase, deacylated by base hydrolysis, and purified by high performance liquid chromatography. Positive and negative ion fast atom bombardment mass spectrometry of the major products isolated by high performance liquid chromatography indicated the following structure for the complete glycoinositol phospholipid anchor. (formula; see text) Methylation of free amino groups by reduction with deuterium instead of hydrogen permitted determination of the number of free amino groups in individual fragment ions as further confirmation of structural assignments. The structure of the glycan portion of the human erythrocyte acetylcholinesterase membrane anchor appears to be similar to that described for Trypanosome brucei variant surface glycoprotein MITat 1.4 (variant 117) (Ferguson, M.A.J., Homans, S.W., Dwek, R.A., and Rademacher, T.W. (1988) Science 239, 753-759) except for the absence of a galactose antenna and the presence of a phosphorylethanolamine on the hexose adjacent to glucosamine.
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PMID:Structural characterization of the glycoinositol phospholipid membrane anchor of human erythrocyte acetylcholinesterase by fast atom bombardment mass spectrometry. 284 7

Incubation at 37 degrees C or treatment of granule membranes of chromaffin cells with Staphylococcus aureus phosphatidylinositol-specific phospholipase C converted from an amphiphilic to a hydrophilic form two proteins with molecular masses of 82 and 68 kDa respectively. Their release is time- and enzyme-concentration-dependent. We showed that they were immunoreactive with an anti-(cross-reacting determinant) antibody known to be revealed only after removal of a diacylglycerol anchor. Furthermore, the action of HNO2 suggests the presence of a non-acetylated glucosamine residue in the determinant. This is one of the first reports suggesting that a glycosylphosphatidylinositol anchor might exist in membranes other than the plasma membrane. We showed that the 68 kDa protein is probably not the subunit of dopamine (3,4-dihydroxyphenethylamine) beta-hydroxylase, an enzyme present in granules in both soluble and membrane-associated forms.
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PMID:Glycosylphosphatidylinositol is involved in the membrane attachment of proteins in granules of chromaffin cells. 285 74

Conditioned medium from Reuber H-35 or Fao hepatoma cells contains autocrine factors that both stimulate DNA synthesis and activate acetyl-coenzyme A (CoA) carboxylase in serum-deprived Fao cells. The factor(s), which appears within 4 h of serum-free culture, also increases the cell number and the mitotic index. The effects of the conditioned medium are insulinomimetic, both with respect to stimulation of DNA synthesis and acetyl-CoA carboxylase activity. However, no induction of tyrosine aminotransferase activity or stimulation of aminoisobutyric acid uptake is seen in response to the conditioned medium. Insulin over a 4-h period does not increase the concentration of DNA synthesis stimulating activity that is observed in the medium. This activity is dialyzable and is resistant to acid treatment or to heating to 60-100 degrees C and to trypsin digestion; it is not extracted with chloroform/methanol nor adsorbed by charcoal or by a C18 reverse-phase column. Fractionation of the conditioned medium derived from Reuber H-35 hepatoma cells by gel filtration chromatography reveals two low molecular weight (less than 1000) compounds that both stimulate DNA synthesis in Fao hepatoma cells. The larger compound (peak I) also stimulates the activity of acetyl-CoA carboxylase. The stimulatory effects of the peak I compound are destroyed by nitrous acid deamination, periodate oxidation, and methanolysis. Biosynthetic labeling studies indicate the probable presence of glucosamine, galactose, and perhaps phosphate in the peak I-activating material. No significant incorporation of either myoinositol or mannose into the active material has been observed. These data, taken together, are consistent with a glycan structure for this autocrine factor, which bears strong resemblance to similar insulinomimetic factors generated in BC3H1 myocytes and H-35 hepatoma cells in response to insulin and on digestion of membranes with a phosphatidylinositol-specific phospholipase C. Further characterization of this factor may provide insight into different pathways of insulin action and could provide a strategy to check autocrine-stimulated tumor growth.
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PMID:An autocrine factor from Reuber hepatoma cells that stimulates DNA synthesis and acetyl-CoA carboxylase. Characterization of biologic activity and evidence for a glycan structure. 289 65

The glycolipids of the protozoan Leishmania major strain LRC-L119 belong to a class of glycoinositol phospholipids (GIPL) that show partial structural homology to the phosphatidylinositol-containing glycolipid membrane anchors of several eukaryotic proteins and the lipid moiety of L. major lipophosphoglycan. The GIPLs were the only glycolipids detected and were purified by octyl-Sepharose and thin layer chromatographies. Analysis of the native and dephosphorylated glycolipids (GIPLs 1-6) by gas chromatography-mass spectrometry revealed that the glycan moieties have between 4 and 10 saccharide residues and all contain mannose, galactose, and non-N-acetylated glucosamine. Some of the GIPLs also contain glucose (GIPL-6) and hexose monophosphate residues (GIPL 4-6). The presence of an inositol phospholipid moiety in all the GIPLs is indicated by the identification of 1 myo-inositol monophosphate residue/molecule and their susceptibility to phosphatidylinositol-specific phospholipase C. However, heterogeneity in the lipid moieties is indicated by differences in the compositional analysis and the behavior of the GIPLs on the thin layer chromatography after mild alkali hydrolysis or phospholipase A2 treatment. These results demonstrate that GIPLs 1-4 contain 1-alkyl-2-acylglycerol composed of saturated unbranched alkyl chains with carbon chain lengths of 18-26 and acyl chains of myristate, palmitate and stearate, whereas GIPL-5 and -6 contain lyso-alkylglycerol composed of mainly C24:0 and C26:0 alkyl chains. Analysis of the products of nitrous acid deamination demonstrates that these glycerolipids are present as alkylacylphosphatidylinositol (GIPLs 1-4) and 1-O-alkylglycerophosphoinositol (GIPL-5 and -6), respectively. GIPL-2 and -3 are labeled on the surface of living promastigotes with galactose oxidase/NaB[3H]4. These GIPLs also react with three monoclonal antibodies that recognize the surface of promastigotes and amastigotes of L. major and other Leishmania spp.
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PMID:A family of glycoinositol phospholipids from Leishmania major. Isolation, characterization, and antigenicity. 291 Aug 65

Insulin binding to plasma membrane receptors results in the generation of substances that acutely mimic the actions of the hormone on certain target enzymes. Two such substances, which modulate the activity of the high-affinity cAMP phosphodiesterase (EC 3.1.4.17), have been purified from hepatic plasma membranes. The two have similar properties and activities but can be resolved by ion-exchange chromatography and high-voltage electrophoresis. They exhibit a net negative charge, even at pH 1.9, and an apparent molecular weight of approximately 1400. The generation of these substances from membranes by insulin can be reproduced by addition of a phosphatidylinositol-specific phospholipase C purified from Staphylococcus aureus. This enzyme is known to selectively hydrolyze phosphatidylinositol and release from membranes several proteins that are covalently linked to phosphatidylinositol by a glycan anchor. Both enzyme-modulating substances appear to be generated by the phosphodiesterase cleavage of a phosphatidylinositol-containing glycolipid precursor that has been characterized by thin-layer chromatography. Some of the chemical properties of these substances have been examined. They appear to be related complex carbohydrate-phosphate substances containing glucosamine and inositol. These findings suggest that insulin may activate a selective phospholipase activity that hydrolyzes a membrane phospholipid, releasing a carbohydrate-containing molecule that regulates cAMP phosphodiesterase and perhaps other insulin-sensitive enzymes.
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PMID:Insulin stimulates the generation from hepatic plasma membranes of modulators derived from an inositol glycolipid. 301 21

Insulin action may involve the intracellular generation of low molecular weight substances that modulate certain key enzymes. The production of two substances that regulate the activity of adenosine 3',5'-monophosphate phosphodiesterase was evaluated in cultured myocytes by incorporation of radiolabeled precursors. Insulin caused the rapid hydrolysis of a chemically undefined membrane glycolipid, resulting in the production of two related complex carbohydrates as well as diacylglycerol. Both the glycolipid precursor and the aqueous products were monitored by labeling with radioactive inositol and glucosamine. Depletion of the labeled precursor and the appearance of labeled water-soluble products and diacylglycerol occurred within 30 seconds after hormone treatment and was followed by rapid resynthesis of the precursor. The aqueous products that were radioactively labeled appeared chromatographically and electrophoretically identical to phosphodiesterase modulating activities produced by insulin from the same cells. The purified radiolabeled and bioactive substances had similar chemical properties. Hydrolysis of the glycolipid precursor and subsequent generation of products could be reproduced by incubation of extracted lipids with a phosphatidylinositol-specific phospholipase C. These studies suggest that insulin stimulates an endogenous, selective phospholipase C activity that hydrolyzes a novel glycolipid, resulting in the generation of a complex carbohydrate-phosphate substance containing inositol and glucosamine that may mediate some of the actions of the hormone.
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PMID:Insulin-stimulated hydrolysis of a novel glycolipid generates modulators of cAMP phosphodiesterase. 301 98


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