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)

When platelets are stimulated by thrombin, a phosphatidylinositol-specific phospholipase C produces a transient rise in 1,2-diacylglycerol. We have now characterized the hydrolysis of diacylglycerol by platelet membranes using doubly isotopically labeled substrates of defined fatty acid composition. We find that the fatty acid at sn-1 is hydrolyzed faster than that at sn-2 thereby producing a 2-monoacylglycerol intermediate. If hydrolysis had occurred at either position randomly, 1-monoacylglycerol would also be produced. That none was detected indicates that either the sn-1 fatty acid must be cleaved first or that 1-monoacylglycerol is hydrolyzed by monoacylglycerol lipase much faster than 2-monoacylglyceol. The latter possibility was excluded by the finding that 1-monoacylglycerol and 2-monoacylglycerol are hydrolyzed at equal rates by platelet membranes. The diacylglycerol lipase cleaves diacylglycerols with sn-1 palmitate as rapidly as those with sn-1 stearate. Arachidonate at sn-2 is cleaved twice as fast as sn-2 oleate by monoacylglycerol lipase. The two activities probably represent discrete enzymes since monoacylglycerol lipase activity can be separated from diacylglycerol lipase by fractionation on DEAE-Sepharose, although both are contained in the membrane fraction of platelets. That the sequential breakdown of 1,2-diacylglycerol also occurs in intact platelets is indicated by our finding of a transient rise in arachidonoyl-monoacylglycerol in thrombin-stimulated platelets. This provides further evidence for a role of the phospholipase C-diacylglycerol lipase pathway in the release of arachidonic acid.
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PMID:Characterization of 1,2-diacylglycerol hydrolysis in human platelets. Demonstration of an arachidonoyl-monoacylglycerol intermediate. 682 11

The effects of polyvalent cations (polyamines and aminoglycoside antibiotics) on Ca2+-dependent phosphatidylinositol-specific phospholipase C activity of human amnion tissue were examined. In the presence of 1 mM Ca2+, the hydrolysis of phosphatidylinositol (2 mM) by phospholipase C was increased greatly (240-560% of control) by spermine (0.4 mM), spermidine (1 mM), neomycin (0.1 mM), gentamicin (0.2 mM), kanamycin (0.4 mM) and streptomycin (0.8 mM). Putrescine and cadaverine (0.1-2.0 mM), however, stimulated phospholipase C activity only slightly. The effects of spermidine, spermine and gentamicin on phospholipase C activity were characterized and found to be dependent upon the concentrations of phosphatidylinositol, Ca2+ and the particular polyvalent cation. At low concentrations of phosphatidylinositol and Ca2+ the predominant effect of polyamines and aminoglycosides was to inhibit phospholipase C activity. When the concentrations of phosphatidylinositol and Ca2+ were increased, spermidine, spermine and gentamicin stimulated phospholipase C activity. In the presence of 16 mM Ca2+, however, phospholipase C activity was maximal and was unaffected by either polyamines or aminoglycosides. At all concentrations of Ca2+ examined, the maximal stimulation of phospholipase C activity by a given polyvalent cation occurred at a fixed molar ratio of the particular polyvalent cation to phosphatidylinositol. Polyamines and aminoglycosides appeared to modulate the Ca2+ requirement for phospholipase C activity, but could not substitute completely for Ca2+. The activities of phospholipase A2, diacylglycerol lipase, monoacylglycerol lipase and diacylglycerol kinase in amnion tissue were unaffected by any of the polyvalent cations examined. It is proposed that any in vivo influences (stimulatory or inhibitory) of polyamines and aminoglycosides on amnion phospholipase C activity would depend upon the effective concentrations of Ca2+ and phosphatidylinositol.
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PMID:The effects of polyamines and aminoglycosides on phosphatidylinositol-specific phospholipase C from human amnion. 684 63

Arachidonic acid (the precursor of prostaglandins of the 2-series and related compounds) is released from phosphatidylinositol in a reaction sequence catalyzed by three enzymes, i.e., phospholipase C, diacylglycerol lipase, and monoacylglycerol lipase. Diacylglycerol, an intermediate in this pathway, was found in human amnion tissue. The fatty acid composition of the diacylglycerol fraction of amnion tissue was very similar to that of the phosphatidylinositol fraction. The diacylglycerol content of human amnion tissue obtained during early labor was greater than that of amnion tissue obtained before the onset of labor. These findings are supportive of the proposition that arachidonic acid is released from the phosphatidylinositol of amnion tissue during human parturition.
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PMID:Initiation of human parturition. 705 44

Lysosomal catabolism of radioactively labelled phosphatidylethanolamine, phosphatidylcholine and several potential metabolites of these diacylphospholipids was studied using rat-liver lysosomes which had been isolated from Triton WR-1339-treated animals. Hydrolysis of these lipids seems to be restricted to the soluble lysosomal compartment. The initial intralysosomal degradation is predominantly catalysed by phospholipase A1 (EC 3.1.1.32) followed by lysophospholipase (EC 3.1.1.5). The end products of this pathway are free fatty acids and glycerophosphorylethanolamine or glycerophosphorylcholine. These phosphodiesters are not hydrolysed further in lysosomes, as has been shown previously (Fowler, S. and De Duve, C. (1969) J. Biol. Chem. 144, 471-481). The intermediary lysophospholipids, however, are also hydrolysed by an alternative pathway, i.e. by a lysophospholipase which catalyses the hydrolysis of the glycerophosphate ester bond, followed by a monoacylglycerol lipase and a phosphomonoesterase (EC 3.1.3.2), respectively. Besides these two catabolic routes of intralysosomal hydrolysis of phosphatidylethanolamine and phosphatidylcholine, additional pathways are possible, which seem, however, to be of minor importance, at least in the substrate concentration ranges employed in these studies. These additional reactions include attack by a phospholipase A2 (EC 3.1.1.4) and--as discovered recently (Matsuzawa, Y. and Hostetler, K.Y. (1980) J. Biol. Chem. 255, 646-652)--by a phospholipase C (EC 3.1.4.3). Cations such as Mg2+, Ca2+, K+ and Na+ inhibit preferentially deacylation reactions.
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PMID:Hydrolytic degradation of phosphatidylethanolamine and phosphatidylcholine by isolated rat-liver lysosomes. 706 64

Arachidonic acid has been implicated as a second messenger in insulin secretion on the basis of (1) mobilization of intracellular Ca2+ from the endoplasmic reticulum of islets and (2) amplification of voltage-dependent Ca2+ entry. The insulin secretagogues D-glucose and the muscarinic agonist carbachol both increase unesterified arachidonic acid accumulation in isolated islets. We now show that diacylglycerol, a product of phospholipase C action, is a major source of free arachidonic acid in islets. Diacylglycerol hydrolysis in islets occurs through a two-step process. In the first step, the sn-1 bond of 1-stearoyl-2-arachidonyl-sn-glycerol is hydrolyzed by a diacylglycerol lipase, giving rise to 2-arachidonyl-sn-glycerol. Next, the sn-2 bond of 2-arachidonyl-sn-glycerol is hydrolyzed by a monoacylglycerol lipase, which is the rate-limiting step, releasing unesterified arachidonic acid. Both diacylglycerol lipase and monoacylglycerol lipase are highly enriched in the plasma membrane of beta-cells. Diacylglycerol lipase activity in islet homogenates is selectively inhibited in a dose-dependent manner by the compound RHC-80267, a specific diacylglycerol lipase inhibitor. RHC-80267 inhibits glucose- and carbachol-induced insulin release from intact islets in a dose-dependent manner that parallels its inhibition of diacylglycerol lipase activity. Importantly, RHC-80267, at concentrations that almost completely inhibit diacylglycerol lipase activity and glucose- and carbachol-induced insulin secretion by islets, markedly inhibits glucose- and carbachol-induced increases in islet arachidonic acid levels, as measured by gas chromatography with electron-capture detection of its pentafluorobenzyl esters. RHC-80267 did not significantly affect islet glucose oxidation, phospholipase C, monoacylglycerol lipase, or phospholipase A2. Since glucose and carbachol are known to stimulate phospholipase C, our observations indicate that diacylglycerol is an important source of arachidonic acid and other free fatty acids in islets. Furthermore, production of arachidonic acid from the hydrolysis of diacylglycerol is essential for glucose- and carbachol-induced insulin secretion.
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PMID:Diacylglycerol hydrolysis to arachidonic acid is necessary for insulin secretion from isolated pancreatic islets: sequential actions of diacylglycerol and monoacylglycerol lipases. 794 36

Endogenous cannabinoid ligands (endocannabinoids) produced by neurons, astrocytes, and microglial cells activate cannabinoid receptors, the molecular target for marijuana's bioactive ingredient Delta(9)-tetrahydrocannabinol. The molecular mechanism underlying the production of the most abundant endocannabinoid, 2-arachidonoylglycerol (2-AG), is unclear. A prevalent hypothesis proposes that activation of metabotropic receptors coupled to the phosphatidylinositol-specific phospholipase C and diacylglycerol (DG) lipase pathway will systematically lead to increases in 2-AG production. Here, we show that ATP increases 2-AG production by cultured microglial cells in a phosphatidylinositol-specific phospholipase C and DG lipase-dependent manner. However, efficacious activation of metabotropic P2Y purinergic receptors coupled to phosphatidylinositol-specific phospholipase C does not increase 2-AG production. This suggests that ionotropic, and not metabotropic, purinergic receptors control 2-AG production at an unexpected enzymatic step of its metabolic pathway. We show that activation of P2X(7) ionotropic receptors, which are highly permeable to calcium, is necessary and sufficient to increase 2-AG production in microglial cells. We also show that the sustained rise in intracellular calcium induced by activation of P2X(7) receptors directly increases DG lipase activity while inhibiting the activity of monoacylglycerol lipase, the enzyme that degrades 2-AG. This inverse sensitivity of DG lipase and monoacylglycerol lipase to calcium constitutes an original and efficient modality for sustained accumulation of 2-AG. Because prolonged increases in 2-AG amounts in brain parenchyma are thought to orchestrate neuroinflammation, the enzymatic steps involved in 2-AG synthesis and degradation by microglial cells constitute appealing targets for therapy aimed at controlling exacerbated neuroinflammation.
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PMID:P2X7 receptors control 2-arachidonoylglycerol production by microglial cells. 1497 57

Endocannabinoids acting on CB(1) cannabinoid receptors are involved in short- and long-term depression of synaptic transmission. The aim of the present study was to determine which endocannabinoid, anandamide or 2-arachidonoylglycerol (2-AG), is involved in depolarization-induced suppression of inhibition (DSI) in the cerebellar cortex, which is the most widely studied form of short-term depression. Depolarization of Purkinje cells in the mouse cerebellum led to an increase in intracellular calcium concentration and to suppression of the inhibitory input to these neurons (i.e. DSI occurred). Orlistat and RHC80267, two blockers of sn-1-diacylglycerol lipase, the enzyme catalysing 2-AG formation, abolished DSI by acting downstream of calcium influx. In contrast, DSI occurred also in the presence of a phospholipase C inhibitor. Intact operation of the calcium-dependent messengers calmodulin and Ca(2+)-calmodulin-dependent protein kinase II were necessary for DSI. DSI was potentiated by an inhibitor of the main 2-AG-degrading enzyme, monoacylglycerol lipase. Interference with the anandamide metabolizing enzyme, fatty acid amide hydrolase, did not modify DSI. Thus, three kinds of observations identified 2-AG as the endocannabinoid involved in DSI in the mouse cerebellum: DSI was abolished by diacylglycerol lipase inhibitors; DSI was potentiated by a monoglyceride lipase inhibitor; and DSI was not changed by an inhibitor of fatty acid amide hydrolase. Further experiments indicated that 2-AG is the endocannabinoid mediating short-term retrograde signalling also at other synapses: orlistat abolished DSI in the rat cerebellum, DSI in the mouse substantia nigra pars reticulata and depolarization-induced suppression of excitation in the mouse cerebellum.
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PMID:Depolarization-induced retrograde synaptic inhibition in the mouse cerebellar cortex is mediated by 2-arachidonoylglycerol. 1697 96

Previously, we reported that intracerebroventricularly (i.c.v.) administered arginine-vasopressin evokes the secretion of noradrenaline and adrenaline from adrenal medulla through the brain phospholipase C- and diacylglycerol-mediated and cyclooxygenase-mediated mechanisms in rats. Diacylglycerol can be hydrolyzed by diacylglycerol lipase to 2-arachidonoyl-sn-glycerol, which may be further degradated by monoacylglycerol lipase to free arachidonic acid, a representative substrate of cyclooxygenase. Recently, 2-arachidonoyl-sn-glycerol has been recognized as a major endocannabinoid, which can modulate synaptic transmission in the brain. In the present experiment, therefore, we examined (1) a role of the brain 2-arachidonoyl-sn-glycerol as a precursor of arachidonic acid in the centrally administered vasopressin-induced elevation of plasma noradrenaline and adrenaline, and (2) a regulatory role of the brain 2-arachidonoyl-sn-glycerol as an endocannabinoid on the vasopressin-induced response, using urethane-anesthetized rats. The vasopressin (0.2 nmol/animal, i.c.v.)-induced elevation of plasma catecholamines was reduced by RHC-80267 (diacylglycerol lipase inhibitor) (1.3 and 2.6 micromol/animal, i.c.v.) and also reduced by MAFP (monoacylglycerol lipase inhibitor) (0.7 and 1.4 micromol/animal, i.c.v.). MAFP (1.4 micromol/animal, i.c.v.) also attenuated the 2-arachidonoyl-sn-glycerol (0.5 micromol/animal, i.c.v.)-induced elevation of plasma catecholamines. AM 251 (cannabinoid CB(1) receptor antagonist) (90 and 180 nmol/animal, i.c.v.) potentiated the vasopressin (0.2 nmol/animal, i.c.v.)-induced response, while AM 630 (cannabinoid CB(2) receptor antagonist) (198 and 793 nmol/animal, i.c.v.) was largely ineffective. In addition, WIN 55212-2 (cannabinoid CB receptor agonist) (188 and 470 nmol/animal, i.c.v.) dose-dependently reduced the vasopressin-induced response. These results suggest that the brain 2-arachidonoyl-sn-glycerol generated from diacylglycerol plays a role as a precursor of arachidonic acid in the centrally administered vasopressin-induced activation of the adrenomedullary outflow, and also negatively regulates the peptide-induced central response through the brain cannabinoid CB(1) receptors in rats.
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PMID:Bidirectional roles of the brain 2-arachidonoyl-sn-glycerol in the centrally administered vasopressin-induced adrenomedullary outflow in rats. 1823 85

Endocannabinoids have been implicated in the regulation of consumption of palatable food, sugar in particular. In this study, we investigated how palatable solutions would affect the hypothalamic mRNA expression of enzymes involved in the synthesis and degradation of the two main endocannabinoids, anandamide and 2-arachidonoyl-glycerol. Rats were offered sugar solutions to drink for one week, during which daily food and drink intake, and body weight gain was monitored. Rats offered sugar solutions to drink consumed less solid food but drank more of their respective sugar solution than did water-drinking control rats, resulting in increased total calorie intake. However, this increase in caloric intake did not result in increased body weight or adiposity in the rats. The mRNA expression of fatty acid amid hydrolase was up-regulated by sucrose and fructose. N-acyl phospatidyl ethanolamine phospholipase D mRNA was up-regulated by sucrose, whereas phospholipase C was down-regulated by all forms of sugar tested. The mRNA expression of monoglyceride lipase was down-regulated by all three forms of sugar. Also, the mRNA expression of diacylglycerol lipase 1alpha was down-regulated by sucrose and fructose, whereas the mRNA expression of diacylglycerol lipase 1beta was up-regulated by fructose. In this study, we show that sugars in liquid form affect enzymes involved in the degradation and synthesis of endocannabinoids in the hypothalamus and that this effect predates obesity.
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PMID:Fructose affects enzymes involved in the synthesis and degradation of hypothalamic endocannabinoids. 2008 90

Membranes are known to respond rapidly to various environmental perturbations by changing their composition and microdomain organization. In previous work we showed that a membrane fluidizer benzyl alcohol (BA) could mimic the effects of heat stress and enhance heat shock protein synthesis in different mammalian cells. Here we explore heat- and BA-induced stress further by characterizing stress-induced membrane lipid changes in mouse melanoma B16 cells. Lipidomic fingerprints revealed that membrane stress achieved either by heat or BA resulted in pronounced and highly specific alterations in lipid metabolism. The loss in polyenes with the concomitant increase in saturated lipid species was shown to be a consequence of the activation of phopholipases (mainly phopholipase A(2) and C). A phospholipase C-diacylglycerol lipase-monoacylglycerol lipase pathway was identified in B16 cells and contributed significantly to the production of several lipid mediators upon stress including the potent heat shock modulator, arachidonic acid. The accumulation of cholesterol, ceramide and saturated phosphoglyceride species with raft-forming properties observed upon both heat and BA treatments of B16 cells may explain the condensation of ordered plasma membrane domains previously detected by fluorescence microscopy and may serve as a signalling platform in stress responses or as a primary defence mechanism against the noxious effects of stresses.
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PMID:Lipidomics reveals membrane lipid remodelling and release of potential lipid mediators during early stress responses in a murine melanoma cell line. 2043 Jan 10


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