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)

To investigate the type of phospholipase activated by agents that stimulate prostaglandin synthesis, we used transformed mouse cells whose phospholipids were doubly labeled with [14C]inositol and [3H]arachidonic acid. [14C]Inositol was incorporated mostly into the phosphatidylinositol and [3H]arachidonic acid was distributed into the various phospholipids. When these cells were incubated with bradykinin, a stimulator of prostaglandin synthesis, the release of 3H radioactivity from cellular phospholipids and the synthesis of prostaglandin were initiated within seconds and reached a maximum in 40 to 70 s. Analysis of the intracellular lipids revealed a concomitant increase of radioactivity associated with lysophosphatidylinositol, which was detectable within 5 s of incubation with bradykinin and reached a maximum between 40 and 70 s. Lysophosphatidylinositol which could be formed either from a phospholipase A1 or phospholipase A2 reaction, was identified by its chromatographic properties and conversion to glycerophosphorylinositol. We found that the 3H/14C ratio of purified lysophosphatidylinositol was 1/11 of that of phosphatidylinositol, which indicated that lysophosphatidylinositol formed in response to bradykinin is 1-acyl-sn-glycero-3-phosphorylinositol and most probably is formed from a phospholipase A2 deacylation of phosphatidylinositol (a phospholipase A1 deacylation would result in the formation of lysophosphatidylinositol of a 3H/14C ratio similar to phosphatidylinositol). Furthermore, we did not detect between control and stimulated cells any significant difference in the level of several phospholipase C metabolites including inositol phosphate, diglyceride, and phosphatidic acid. These results suggest that phospholipase C is probably not activated. The formation of lysophosphatidylinositol was also stimulated by thrombin and ionophore A23187, both activators of prostaglandin synthesis. Dexamethasone, a lipase inhibitor, inhibited the appearance of lysophosphatidylinositol, whereas aspirin and low concentrations of indomethacin, the cyclooxygenase inhibitor, did not inhibit. The results presented in ths paper provide evidence that a phospholipase A2-hydrolyzing phosphatidylinositol is activated when intact cells are stimulated for prostaglandin synthesis.
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PMID:The activation of phosphatidylinositol-hydrolyzing phospholipase A2 during prostaglandin synthesis in transformed mouse BALB/3T3 cells. 678 79

In this short review recent results obtained on platelet phospholipid metabolism are summarized. The first part reports a topological study of arachidonic acid (AA) replacement in platelet phospholipids. It is shown that incubation of platelets with radioactive free arachidonic acid leads to a labelling of the phospholipids present inside the platelet, whereas the exchange of intact phosphatidylcholine (PC) molecules with the plasma lipoproteins occurs on the platelet outer surface. This should allow a selective labelling of the small external pool of AA in order to follow its behaviour during platelet activation. In the second part, some enzymes involved in the metabolism of phosphatidylinositol (PI) have been further characterized. The first one is a diglyceride-lipase, which is located in the plasma membrane and releases the two fatty acids esterifying the diglycerides formed from PI by the action of the platelet phospholipase C. Such an enzyme is probably responsible for the release of AA from PI occurring upon platelet activation. On the other hand, cytosolic phospholipid exchange proteins able to catalyse the transfer of PI between membranes have been identified. The possible role of the enzymes involved in the acceleration of PI turnover occurring during platelet activation is discussed.
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PMID:Studies on topological distribution of arachidonic acid replacement in platelet phospholipids and on enzymes involved in the phospholipid effect accompanying platelet activation. 680 31

By using a suckling mouse assay, heat-stable enterotoxin (ST) was purified from the culture filtrate of Yersinia enterocolitica isolated from a diarrheal patient. The purification procedures involve ultrafiltration with an Amicon HIP-10 hollow fiber, ethanol fractionation, protamine sulfate treatment, diethylaminoethyl-Sephacel and hydroxylapatite column chromatographies, and Sephacryl S-200 superfine gel filtration. About 408-fold purification was achieved, with a yield of 12.0%. The minimal effective dose of purified ST was about 110 ng in the suckling mouse assay. The molecular weight of purified ST was 9,000 by Sephadex G-100 superfine gel filtration. The purified ST was stable to heating (100 degrees C for 20 min, 121 degrees C for 20 min) and did not lose its toxicity after treatment with protease, trypsin, lipase, phospholipase C, ribonuclease, deoxyribonuclease, beta-glucosidase, and neuraminidase. The purified ST was separated by isoelectric focusing into two active fractions, with pI's of 3.29 (ST-1) and 3.00 (ST-2), respectively. Antiserum from guinea pigs immunized with the purified ST neutralized the activity of both Y. enterocolitica ST and Escherichia coli ST.
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PMID:Partial purification and characterization of heat-stable enterotoxin produced by Yersinia enterocolitica. 721 60

Lipase and phospholipase C from Staphylococcus aureus could be isolated by gel filtration on Sephacryl S 200 (Fig. 1a, b) and completely separated by refiltration under the same conditions. Isoelectric focusing gave maximal enzyme-activities for lipase at pH 8.6 and 9.5 and for phospholipase C at pH 7.4 (Fig. 2). Thin-layer chromatography revealed that the reaction products in lecithin agar of the phospholipase C-preparations from S. aureus and Bacillus cereus were identical (Table 1).
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PMID:[Lipase and phospholipase from Staphylococcus aureus of different origin. II. Purification and characterization (author's transl)]. 722 22

The lipolytic action of theophylline was examined using both intact fat cells and a fat globule system. Theophylline had similar lipolytic actions in both systems. However theophylline did not activate hormone-sensitive lipase in the fat globule system as measured with added Ediol. Pretreatment of the fat globules with phospholipase C suppressed theophylline-induced lipolysis, but phospholipase D had no effect. A theophylline-sensitive system was reconstituted from endogenous fat and a lipase fraction. Inhibitors of theophylline-induced lipolysis such as quinine and propranolol inhibited theophylline binding to artificial lipid micelles. Purine nucleosides such as adenosine, inosine and guanosine inhibited theophylline-induced lipolysis in the fat globule system. These results suggest that theophylline has a lipolytic action similar to that of adrenaline. Both share a lipolytic mechanism additional to that involving the activation of hormone sensitive lipase through the cyclic-AMP dependent protein kinase. Phospholipids play an important role in this additional mechanism.
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PMID:The mechanism of the lipolytic action of theophylline in fat cells. 724 46

High enriched (50- to 70-fold) fractions of "native" lysosomes were isolated using continuous flow electrophoresis from livers of rats which had not been pretreated with Triton WR-1339. Incubation of lysosomes for 30 min at pH 5.0 in the presence of 5 mM EDTA resulted in a dramatic loss in the content of fatty acids bound to triacylglycerols (137 down to 10 mumol/mg protein) and to phospholipids and an elevation in the level of unesterified fatty acid. Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin concentrations decreased whereas those of lysophosphatidylethanolamine (0.8 up to 8.5% of total lipid-P) and lysophosphatidylcholine (1.9 up to 16.7%) rose in a manner parallel to their respective, fully acylated lipids. Other phospholipids, including phosphatidylinositol, did not change in concentration during incubation. These results indicate that lysosomal phospholipase A, sphingomyelin and triacylglycerol lipase are activated by incubation at acid pH, enabling them to hydrolyze endogenous lysosomal lipids. However, lysosomal phosphatidylinositol-directed phospholipase C is apparently unable to interact with phosphatidylinositol of the lysosomal membrane.
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PMID:Endogenous lipolytic activities during autolysis of highly enriched hepatic lysosomes. 731 38

We recently proposed a new pathway by which arachidonate is released from platelet phosphatidyl inositol after stimulation by either thrombin or calcium ionophore A23187. The initial step in arachidonate liberation involves hydrolysis of phosphatidyl inositol to form 1,2-diacyglycerol which is subsequently hydrolyzed by a diacyglycerol lipase to liberate arachidonate for the prostaglandin and lipoxygenase pathways. Whether this pathway is unique to platelets or accounts for arachidonate release from other tissues has not been previously studied. Thus we have now investigated arachidonate metabolism in mouse fibrosarcoma cells (HSDM1C1) grown in culture. These cells contain approximately 7.6% of their total phospholipid as phosphatidyl inositol in the resting state (range 6.5-8.3%). When bradykinin (12 microM) is added to the fibrosarcoma cells, there is a rapid depletion of membrane phosphatidyl inositol reaching 62 +/- 8% S.D. of baseline values by 15 seconds, falling to 36 +/- 6% by 15 minutes. The drop in membrane phosphatidyl inositol is accompanied by release of arachidonate and PGE2 into the culture medium. The time course of phosphatidyl inositol breakdown and PGE2 formation supports the idea that phosphatidyl inositol breakdown provides he arachidonate for prostaglandin synthesis in mouse fibrosarcoma cells. Crude extracts of HSDM1C1 cells contained sufficient phosphatidyl inositol-specific phospholipase C activity and diacylglycerol lipase activity to account for arachidonate release in these cells.
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PMID:Bradykinin-stimulated release of arachidonate from phosphatidyl inositol in mouse fibrosarcoma cells. 741 91

xpr, a regulatory element of exoprotein synthesis in Staphylococcus aureus, defined by an insertion of Tn551 into the chromosome of strain S6C, affects the expression of several exoproteins at the mRNA level. Drastic reduction in transcript levels for staphylococcal enterotoxin B (seb), lipase (geh), alpha-toxin (hla), and delta-toxin (hld) were detected, while mRNA levels for coagulase (coa) and protein A (spa) were elevated. Because the delta-toxin gene resides within the RNAIII transcript of the exoprotein regulator, agr, the reduction in hld message in the mutant strain of S6C is indicative of additional regulatory events in exoprotein gene expression. Northern (RNA) analysis of total cellular RNA hybridized with probes specific for RNAII and RNAIII (the two major transcripts of the agr operon) showed that both transcripts were reduced 16- to 32-fold at 3 h (late exponential phase) and 8- to 16-fold at 12 h (postexponential phase). These data confirm our original findings (M. S. Smeltzer, M. E. Hart, and J. J. Iandolo, Infect. Immun. 61:919-925, 1993) that two regulatory loci, agr and xpr, are interactive at the genotypic level.
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PMID:The extracellular protein regulator (xpr) affects exoprotein and agr mRNA levels in Staphylococcus aureus. 750 65

Membrane phospholipid degradation has been proposed to play a key role in hypoxic-ischemic brain injury. We tested the hypotheses that both nordihydroguaiaretic acid, a phospholipase A2 and lipoxygenase inhibitor, and RHC 80267, a diacylglycerol lipase inhibitor, would decrease the release of [3H]arachidonic acid metabolites from prelabeled cultures of astroglia subjected to combined glucose-oxygen deprivation and that these inhibitors would also decrease astroglial injury during combined glucose-oxygen deprivation. Both nordihydroguaiaretic acid and RHC 80267 significantly inhibited the release of [3H]arachidonic acid metabolites during combined glucose-oxygen deprivation. This suggests that two separate enzymic pathways, the phospholipase A2 pathway and the phospholipase C/diacylglycerol lipase pathway, contribute to the release of astroglial [3H]arachidonic acid metabolites during combined glucose-oxygen deprivation. However, both of these lipase inhibitors increased astroglial cell death during combined glucose-oxygen deprivation, probably due to inhibition of arachidonic acid release. We speculate that arachidonic acid release may be a mechanism of astroglial self-preservation during combined glucose-oxygen deprivation.
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PMID:Nordihydroguaiaretic acid and RHC 80267 potentiate astroglial injury during combined glucose-oxygen deprivation. 754 17

The mechanism of arachidonic acid (AA) release in collagen-activated human platelets was studied. An arachidonic acid metabolite, thromboxane B2 (TXB2), was formed in parallel with the formation of phosphatidic acid (PA) without formation of lysophosphatidic acid (lysoPA) or lysophosphatidylinositol (lysoPI) in the absence of extracellular Ca2+, suggesting that AA was released from PI via a PI-specific phospholipase C (PI-PLC)/diacylglycerol (DG) lipase/monoacylglycerol (MG) lipase pathway under the cytosolic low Ca2+ concentrations. Moreover, solubilized DG lipase and MG lipase could hydrolyze the substrates at basal cytosolic free Ca2+ concentrations. Subsequently, the relationship of cytosolic free Ca2+ concentrations and formation of AA metabolites was analyzed using Ca2+ ionophore, A23187. Collagen was able to induce a release of small amounts of AA under basal cytosolic Ca2+ conditions. However, a release of large amounts of AA was induced by phospholipase A2 activated by both collagen-receptor occupancy and elevated Ca2+ levels. A TXA2 mimetic agonist, STA2 induced all the responses except for AA release. From these results, the mechanism of AA release and signal transduction in collagen-activated human platelets is discussed.
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PMID:The mechanism of arachidonic acid release in collagen-activated human platelets. 776 21


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