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)

Ectoenzyme release from porcine intestinal brush border membranes by phosphatidylinositol-specific phospholipase C of Bacillus thuringiensis was studied. Alkaline phosphodiesterase I, alkaline phosphatase and 5'-nucleotidase were released from both slices and brush border membranes. The pattern of alkaline phosphodiesterase I release was the same as that of alkaline phosphatase. The release of alkaline phosphodiesterase I induced by phospholipase C was dependent on, or proportional to, the reaction time and the concentration of phospholipase C. The Arrhenius plot for phosphodiesterase I release showed a single break at 30 degrees C for brush border membranes. Only 40% of alkaline phosphodiesterase I present in the brush border membranes were solubilized by phosphatidylinositol-specific phospholipase C treatment. The data indicate the presence of two forms of phosphodiesterase I, which are different in their sensitivity to phospholipase C. The released alkaline phosphodiesterase I had a molecular weight of 240,000 and was activated by Mg2+ and Ca2+, but strongly inhibited by EDTA.
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PMID:Alkaline phosphodiesterase I release from eucaryotic plasma membranes by phosphatidylinositol-specific phospholipase C. II. The release from brush border membranes of porcine intestine. 302

Despite their physicochemical and mechanistic differences platelet activating factor (or acetylglycerylether phosphorylcholine; AGEPC) and thrombin, both platelet stimulatory agents, induce phosphoinositide turnover in platelets. We therefore investigated the stimulation of the phosphoinositide phosphodiesterase by these agents and questioned whether they evoked hydrolysis of the same or different pools of phosphoinositides. [3H]Inositol-labelled rabbit platelets were challenged with thrombin and/or AGEPC under a variety of protocols, and the phospholipase C mediated production of radioactive inositol monophosphate (IP); inositol bisphosphate (IP2) and inositol trisphosphate (IP3) was used as the parameter. AGEPC (1 X 10(-9) M) caused a transient maximum (5 to 6-fold) increase in [3H]IP3 at 5 s followed by a decrease. Thrombin (2 U/ml) elicited an increase in [3H]IP3 at a much slower rate than AGEPC; 2 fold at 5 s, 5 fold at 30 s and a maximum 6 to 8-fold at 2-5 min. Compared to AGEPC, thrombin stimulated generation of [3H]IP2 and [3H]IP were severalfold higher. When thrombin and AGEPC were added together to platelets there was no evidence for an additive increase in inositol polyphosphate levels except at earlier time points where increases were submaximal. When AGEPC was added at various time intervals after thrombin pretreatment, no additional increases in [3H]IP3 were observed over that maximally seen with thrombin or AGEPC alone. In another set of experiments, submaximal increases (about 1/4 and 1/2 of maximum) in [3H]IP3 were achieved by using selected concentrations of thrombin (0.1 U and 0.3 U, respectively) and then AGEPC (1 X 10(-9) M) was added for 5 s. Once again the increase in [3H]IP3 was close to the maximal level seen with thrombin or AGEPC individually. It is concluded that thrombin and AGEPC differentially activated phosphoinositide phosphodiesterase (phospholipase C) in rabbit platelets and that the stimulation of the phospholipase C by these two stimuli causes IP3 production via hydrolysis of a common pool of phosphatidylinositol 4,5-bisphosphate.
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PMID:Activation of phospholipase C in platelets by platelet activating factor and thrombin causes hydrolysis of a common pool of phosphatidylinositol 4,5-bisphosphate. 303 49

In ventilated rats, levels of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), diacylglycerol (DAG), triacylglycerol (TAG), free fatty acids (FFA) and phosphatidic acid, as well as their fatty acid contents, were measured in forebrain tissue after 1, 20 and 60 min of seizures induced by bicuculline. Cerebral energy state was also measured. PI decreased progressively throughout 60 min of seizures, whereas the levels of PIP and PIP2 did not change. DAG increased modestly and persistently. FFA increased markedly during the early seizure period, but decreased later. Following an initial drop, TAG rose above control. Phosphatidic acid did not change. The levels of ATP and energy charge potential decreased slightly and lactate accumulated. Stearic acid (18:0) and arachidonic acid (20:4) primarily accounted for the changes in the levels of the lipids. At the onset of seizures, the decrease of 18.0 and 20:4 in PI occurred in parallel with an enrichment of these fatty acids in FFA and DAG. Despite the fact that the losses of 18:0 and 20:4 from PI were quantitatively similar to each other at all times examined, the increase in free 18:0 was much larger than the increase in free 20:4 at 20 min of seizures. Concurrently there was a rise of 20:4 in TAG. As the FFA levels declined thereafter, 20:4 and docosahexaenoate (22:6) in TAG continued to increase. The results are consistent with the view that seizure activity stimulates the hydrolytic breakdown of brain phosphoinositides--the pathway catalyzed by phosphodiesterase of the phospholipase C type followed by lipases, and probably the pathway catabolized by phospholipases A as well. Preferential incorporation of polyunsaturated fatty acids into TAG-acyl residues may represent a mechanism to reduce the level of their free forms when the latter are produced in large amounts.
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PMID:Cerebral phosphoinositide, triacylglycerol and energy metabolism during sustained seizures induced by bicuculline. 303 62

Labeling with [3H]galactose was employed to isolate a glycosylphosphatidylinositol from rat hepatocytes which might be involved in the action of insulin. The polar head group of this glycosylphosphatidylinositol was generated by phosphodiesterase hydrolysis with a phosphatidylinositol-specific phospholipase C from Bacillus cereus. By Dowex AG1 x 8 chromatography the polar head group could be separated into three radioactive peaks eluting at 100 mM (peak I), 200 mM (peak II) and 500 mM (peak III) ammonium formate, respectively. Peak III was the most active as an inhibitor of the cAMP-dependent protein kinase. Treatment of peak III with alkaline phosphatase markedly reduced its activity on cAMP-dependent protein kinase. When peaks I, II or III were treated with alkaline phosphatase and analyzed again by Dowex AG1 x 8 chromatography, the radioactivity eluted with the aqueous fraction. The above results indicate that the polar head group of the insulin-sensitive glycosylphosphatidylinositol from rat hepatocytes exists in three different phosphorylated forms and that the biological activity of this molecule depends on its phosphorylation state.
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PMID:Different phosphorylated forms of an insulin-sensitive glycosylphosphatidylinositol from rat hepatocytes. 304 67

Inositol phospholipid degradation and release of phospholipid-bound arachidonic acid was induced in intact peritoneal macrophages by exposure to phorbol myristate acetate (PMA) or zymosan particles. PMA, known to activate protein kinase C, selectively enhanced the deacylation of phosphatidylinositol (i.e., degradation by phospholipase A), while zymosan particles enhanced degradation via both phospholipase A and inositol lipid phosphodiesterase (phospholipase C). The release of arachidonic acid was found to correlate with the degradation of phosphatidylinositol by the phospholipase A pathway and could be dissociated from the phospholipase C-catalyzed cleavage of inositol phospholipids in several experimental situations: (i) when PMA was the stimulus, (ii) by the difference in Ca2+ dependence between the two enzymatic processes when zymosan was the stimulus and (iii) by the parallel inhibition by chlorpromazine of the phospholipase A pathway and arachidonic acid release, but not inositol phospholipid phosphodiesterase. In addition, phloretin, a reported inhibitor of protein kinase C, was found to inhibit arachidonic acid release and the deacylation of phosphatidylinositol. The results are consistent with a model in which arachidonic acid release is mediated by phospholipase(s) A and in which PMA or the phosphodiesterase-catalyzed degradation of phosphoinositides causes activation of the phospholipase A pathway via protein kinase C.
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PMID:Evidence for a catalytic role of phospholipase A in phorbol diester- and zymosan-induced mobilization of arachidonic acid in mouse peritoneal macrophages. 308 22

The plasma membranes of bovine adrenal chromaffin cells were isolated and the activities of enzymes involved in arachidonic acid liberation were investigated. Only a minute activity of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) could be detected using externally added phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as substrate. When membranes were treated with exogenous phospholipase C (orthophosphoric acid diester phosphohydrolase, EC 3.1.4.1) there was a liberation of free fatty acids from the sn-2 position of PC. The enzyme responsible for this effect could be demonstrated to be a diacylglycerol lipase (glycerol ester hydrolase, EC 3.1.1.3) localized in the plasma membrane. Using phosphatidylinositol (PI) as a substrate, it was found that an endogenous phospholipase C exists which co-purifies with the membrane preparation. The produced diacylglycerol is subsequently hydrolyzed by diacylglycerol lipase liberating arachidonic acid. The two enzymes, phospholipase C and diacylglycerol lipase were characterized. Phospholipase C was found to be calcium dependent and PI specific, showing an activity of 60 pmol/micrograms protein per h (1.2 mM Ca2+), whereas the diacylglycerol lipase was calcium independent hydrolyzing diacylglycerol at a rate of 7.2 pmol/micrograms protein per h. The lipase but not the phospholipase C was inhibited 50% by 1.7 mM para-bromophenacylbromide.
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PMID:Phospholipase C and diacylglycerol lipase activities associated with plasma membranes of chromaffin cells isolated from bovine adrenal medulla. 308 88

The possible participation of the regulatory proteins Ns and Ni in the regulation of phospholipase C activity in rat pancreatic islets was investigated. The islets were preincubated for 120 min with myo-[2-3H]inositol and the fractional outflow rate of [3H]inositol or production of [3H]inositol 1-phosphate was then measured. Glucagon failed to affect these metabolic variables, whether in the absence or presence of D-glucose. Pretreatment of the islets with cholera toxin also failed to affect basal or glucose-stimulated [3H]inositol outflow. Likewise, clonidine, which abolished insulin release evoked by D-glucose and carbamylcholine, failed to prevent the stimulant action of these secretagogues upon either [3H]inositol outflow or [3H]inositol 1-phosphate production. It is concluded that the regulatory proteins Ns and Ni apparently do not play any major role in the regulation of phosphoinositide phosphodiesterase activity in islet cells.
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PMID:Unresponsiveness of phospholipase C to the regulatory proteins Ns and Ni in pancreatic islets. 310 94

Hydrolysis of polyphosphoinositides by phosphodiesterase has been demonstrated to be involved in the control of cytosolic Ca2+ concentrations. The stimulation of Ca2+ ionophores of the release of inositol phosphates in macrophages, and other cells, together with the Ca2+ requirements for zymosan-induced phospholipase C activation, make unclear the relationship between Ca2+ mobilization and polyphosphoinositide hydrolysis. The results in the present paper strongly suggest that, for zymosan-induced phospholipase C activation, a previous increase in cytosolic Ca2+ is not a required event. These results also show that zymosan-activated release of inositol phosphates may be mediated by a guanine-nucleotide-binding protein.
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PMID:Zymosan-induced release of inositol phosphates at resting cytosolic Ca2+ concentrations in macrophages. 310 91

The hydrolysis of [3H]phosphatidylinositol (PI) and [3H]phosphatidylinositol-4,5-bisphosphate (PIP2) by cytosolic inositide phosphodiesterase (phospholipase C) from Ehrlich ascites tumour cells was determined. Cytosolic fractions were prepared from tumour cells that had been cultivated for two days at low serum level (2%) in the presence of 1-oleoyl-2-acetyl-sn-glycerol (OAG). Cytosols from unstimulated cells (2% serum without OAG) were used for comparison. Phospholipase C acting on PI and PIP2 was significantly inhibited in the cytosol of OAG-stimulated cells. The suppressed enzyme was activated by Ca2+ and also by the guanine nucleotide GTP in a concentration-dependent manner independently of calcium ions. In the presence of Ca2+, GTP exerted a synergistic stimulatory effect. In contrast, GTP and GTP gamma S showed no effect on the phospholipase C activity of unstimulated cells. It is suggested that the suppressed PI- and PIP2-specific enzyme activity can be modulated by its susceptibility to Ca2+ ions and GTP probably via the GTP-binding protein.
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PMID:Guanine nucleotides activate cytosolic phospholipase C of ascites tumour cells stimulated by 1-oleoyl-2-acetyl-sn-glycerol. 325 Sep 42

We recently described the insulin-dependent release of a carbohydrate substance from plasma membranes which regulated certain intracellular enzymes (Saltiel, A. R., and Cuatrecasas, P. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 5793-5797). This enzyme-modulating substance appeared to arise from the phosphodiesterase hydrolysis of a novel inositol-containing glycolipid. This is supported by observations that insulin stimulated the rapid generation of [3H]myristate-labeled diacylglycerol in cultured BC3Hl myocytes. Myristoyl diacylglycerol production in these cells was unaffected by epinephrine, although arachidonate-labeled diacylglycerol was rapidly produced in response to stimulation by this alpha-1 adrenergic agent. The production of distinct species of diacylglycerol was apparently due to hormonally specific hydrolysis of different precursors. A novel glycolipid was identified on silica TLC or high pressure liquid chromatography which served as a substrate for the insulin-stimulated phosphodiesterase reaction. This glycolipid was metabolically labeled with radioactive inositol, glucosamine, and myristic acid, suggesting a phosphatidylinositol (PI)-glycan structure. Treatment of this glycolipid with a PI-specific phospholipase C resulted in the generation of two products: an inositol phosphate-glycan which modulated the activity of the low Km cAMP phosphodiesterase and myristoyl diacylglycerol. Insulin caused the rapid hydrolysis of the PI-glycan, which was then apparently resynthesized. These data further suggest that insulin stimulates the activity of a phospholipase C which selectively hydrolyzes a novel PI-glycan, releasing a carbohydrate enzyme modulator as well as a unique species of diacylglycerol.
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PMID:Insulin-stimulated diacylglycerol production results from the hydrolysis of a novel phosphatidylinositol glycan. 354 98


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