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)

Guanyl-5'-yl imidodiphosphate (p[NH]ppG) stimulated a rapid phospholipase C-mediated breakdown of exogenously added phosphatidylinositol 4,5-bisphosphate (PIP2) in rat cerebral-cortical membranes, with half-maximal activation at approx. 33 microM. NaF stimulated phospholipase C activity, with half-maximal activation at 0.5 mM. Stimulation of phospholipase C activity by NaF exhibited pH optima at approx. 5.5 and 7.0, with the stimulatory activity at pH 7.0 greater than that at pH 5.5. With p[NH]ppG, only stimulation at pH 7.0 was observed. Neither p[NH]ppG nor NaF stimulated hydrolysis of added phosphatidylinositol (PI) or phosphatidylinositol 4-phosphate (PIP). Mg2+ (0.5 mM) potentiated p[NH]ppG-stimulated breakdown of PIP2. Ca2+ increased basal and p[NH]ppG-stimulated breakdown of PIP2. PI breakdown was stimulated only by high Ca2+ concentrations and was unaffected by p[NH]ppG at any Ca2+ concentration examined. These results indicate that, in cerebral-cortical membranes, activation of phospholipase C by guanine nucleotides or fluoride directly increases a phospholipase C activity which specifically hydrolyses PIP2.
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PMID:Guanine nucleotide and NaF stimulation of phospholipase C activity in rat cerebral-cortical membranes. Studies on substrate specificity. 282 1

Incubation of rat brain synaptosomes prelabeled with [2-3H]inositol resulted in a time-dependent release of labeled inositol 1-phosphate. This process was Ca2+ dependent, and ATP (1 mM) enhanced the inositol 1-phosphate formation three- to fivefold. Using [1-14C]arachidonoyl-phosphatidylinositol which was introduced into saponin-permeabilized synaptosomes, ATP (1 mM) and free Ca2+ (approximately 20 microM) enhanced the phospholipase C hydrolysis of this substrate to form labeled diacylglycerol. When the same permeabilized synaptosomal preparation was incubated with [2-3H]inositol-phosphatidylinositol, ATP not only enhanced the formation of labeled inositol 1-phosphate, but also inhibited the conversion of inositol 1-phosphate to inositol. Furthermore, ATP appeared to reduce the Ca2+ requirement of the phosphatidylinositol-phospholipase C. Inhibition of the conversion of inositol 1-phosphate to inositol could not be overcome by increasing the Mg2+ concentration in the incubation medium. Although the ATP effect is not viewed as a receptor-mediated event, it is possible that such an event may occur in synaptosomes under conditions in which intrasynaptic Ca2+ concentration becomes elevated.
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PMID:Effects of ATP on phosphatidylinositol-phospholipase C and inositol 1-phosphate accumulation in rat brain synaptosomes. 282 92

A phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]-hydrolytic activity was found to be present in the human platelet membrane fraction, with 20% of the total activity of the homogenate. The membrane-associated phospholipase C activity was extracted with 1% deoxycholate (DOC). The DOC-extractable phospholipase C was partially purified approx. 126-fold to a specific activity of 0.58 mumol of PtdIns-(4,5)P2 cleaved/min per mg of protein, by Q-Sepharose, heparin-Sepharose and Ultrogel AcA-44 column chromatographies. This purified DOC-extractable phospholipase C had an Mr of approx. 110,000, as determined by Ultrogel AcA-44 gel filtration. The enzyme exhibits a maximal hydrolysis for PtdIns-(4,5)P2 at pH 6.5 in the presence of 0.1% DOC. The addition of 0.1% DOC caused a marked activation of both PtdIns(4,5)P2 and phosphatidylinositol (PtdIns) hydrolyses by the enzyme. The enzyme hydrolysed PtdIns(4,5)P2 and PtdIns in a different Ca2+-dependent manner; the maximal hydrolyses for PtdIns(4,5)P2 and PtdIns were obtained at 4 microM- and 0.5 mM-Ca2+ respectively. In the presence of 1 mM-Mg2+, PtdIns(4,5)P2-hydrolytic activity was decreased at all Ca2+ concentrations examined, but PtdIns-hydrolytic activity was not affected.
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PMID:Characterization of partially purified phospholipase C from human platelet membranes. 282 27

The effect of the GTP analogue guanosine 5'-[gamma-thio]triphosphate (GTP[S]) on the polyphosphoinositide phospholipase C (PLC) of rat liver was examined by using exogenous [3H]phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. GTP[S] stimulated the membrane-bound PLC up to 20-fold, with a half-maximal effect at approx. 100 nM. Stimulation was also observed with guanosine 5'-[beta gamma-imido]triphosphate, but not with adenosine 5'-[gamma-thio]triphosphate, and was inhibited by guanosine 5'-[beta-thio]diphosphate. Membrane-bound PLC was entirely Ca2+-dependent, and GTP[S] produced both a decrease in the Ca2+ requirement and an increase in activity at saturating [Ca2+]. The stimulatory action of GTP[S] required millimolar Mg2+. [8-arginine]Vasopressin (100 nM) stimulated the PLC activity approx. 2-fold in the presence of 10 nM-GTP[S], but had no effect in the absence of GTP[S] or at 1 microM-GTP[S]. The hydrolysis of PtdIns(4,5)P2 by membrane-bound PLC was increased when the substrate was mixed with phosphatidylethanolamine, phosphatidylcholine or various combinations of these with phosphatidylserine. With PtdIns(4,5)P2, alone or mixed with phosphatidylcholine, GTP[S] evoked little or no stimulation of the PLC activity. However, maximal stimulation by GTP[S] was observed in the presence of a 2-fold molar excess of phosphatidylserine or various combinations of phosphatidylethanolamine and phosphatidylserine. Hydrolysis of [3H]phosphatidylinositol 4-phosphate by membrane-bound PLC was also increased by GTP[S]. However, [3H]phosphatidylinositol was a poor substrate, and its hydrolysis was barely affected by GTP[S]. Cytosolic PtdIns(4,5)P2-PLC exhibited a Ca2+-dependence similar to that of the membrane-bound activity, but was unaffected by GTP[S]. It is concluded that rat liver plasma membranes possess a Ca2+-dependent polyphosphoinositide PLC that is activated by hormones and GTP analogues, depending on the Mg2+ concentration and phospholipid environment. It is proposed that GTP analogues and hormones, acting through a guanine nucleotide-binding protein, activate the enzyme mainly by lowering its Ca2+ requirement.
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PMID:Guanine-nucleotide and hormone regulation of polyphosphoinositide phospholipase C activity of rat liver plasma membranes. Bivalent-cation and phospholipid requirements. 282 42

Recently we demonstrated the presence in calf thymocytes of a GTP-binding protein (G-protein) composed of three polypeptides, 54, 41, and 27 kDa, which was physically and functionally associated with a soluble phosphoinositides-specific phospholipase C (PI-phospholipase C). The properties of this G protein were further investigated with the following results. 1) In addition to the ability to bind [35S]guanosine-5'-[gamma-thio]triphosphate (GTP gamma S), the G-protein exhibited GTPase activity, which was enhanced by Mg2+, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, but inhibited by sodium cholate, GTP gamma S and F-.2) The 54-kDa polypeptide was ADP-ribosylated by pertussis toxin and also by endogenous membrane-bound ADP-ribosyltransferase, but none of these three polypeptides was ADP-ribosylated by cholera toxin. 3) The G-protein did not cross-react with either anti-rat brain alpha 1 (alpha-subunit of inhibitory G-protein, G1), alpha 0 (alpha-subunit of other G1-like G-protein, G0) or beta gamma antibodies. 4) Incubation of this G Protein with GTP gamma S caused dissociation of the three polypeptides. 5) The 27 kDa polypeptide showed GTP-binding activity and enhanced the phosphatidylinositol 4,5-bisphosphate hydrolysis by purified PI-phospholipase C. These results suggest that the PI-phospholipase C-associated G-protein in calf thymocytes may be a novel one and that it is involved in the regulation of PI-phospholipase C activity.
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PMID:Properties of a novel GTP-binding protein which is associated with soluble phosphoinositides-specific phospholipase C. 283 52

An occurrence of phosphatidylinositol 4,5-bisphosphate (PIP2) phosphomonoesterase in human platelets was demonstrated by analyzing phosphoinositides metabolism. The activity of the enzyme was maximum at pH 7.0. It was active even in the absence of Ca2+ or Mg2+ but it was enhanced in the presence of Mg2+ or NaF. The activity was inhibited by pyrophosphate. The activity was not altered in the presence of Ca2+. Thereby, besides phosphodiesteric cleavage by phospholipase C, the amount of PIP2 in activated platelets may be reduced by the combined effect of PIP2-phosphomonoesterase and suppressed activity of PI-kinase by Ca2+.
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PMID:Studies on PIP2-phosphomonoesterase activity in human platelets. 283 87

[3H]Inositol-labelled GH3 rat anterior pituitary tumour cells were permeabilized with digitonin and were incubated at 37 degrees C in the presence of ATP and Mg2+. [3H]Polyphosphoinositide breakdown and [3H]inositol phosphate production were stimulated by hydrolysis-resistant GTP analogues and by Ca2+. Of the nucleotides tested, guanosine 5'-[gamma-thio]triphosphate (GTP gamma S) was the most effective stimulus. Activation by GTP gamma S appeared to be mediated by a guanine nucleotide-binding (G) protein as GTP gamma S-stimulated [3H]inositol phosphate production was inhibited by other nucleotides with a potency order of GTP = GDP = guanosine 5'-[beta-thio]diphosphate greater than ITP greater than GMP greater than UTP = CTP = adenosine 5'-[gamma-thio]triphosphate. The stimulatory effects of 10 microM-GTP gamma S on [3H]inositol phosphate levels were reversed by spermine and spermidine with IC50 values of approx. 0.25 and 2 mM respectively. Putrescine was inhibitory only at higher concentrations. Similarly, GTP gamma S-induced decreases in [3H]polyphosphoinositide levels were reversed by 2.5 mM-spermine. The inhibitory effects of spermine were not overcome by supramaximal concentrations of GTP gamma S. In contrast, [3H]inositol phosphate production stimulated by addition of 0.3-0.6 mM-Ca2+ to incubation media was only partially inhibited by spermine (5 mM), and spermine was not inhibitory when added Ca2+ was increased to 1 mM. These data show that polyamines, particularly spermine, inhibit phospholipase C-catalysed polyphosphoinositide hydrolysis with a marked selectivity towards the stimulatory effects of GTP gamma S.
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PMID:Polyamines inhibit phospholipase C-catalysed polyphosphoinositide hydrolysis. Studies with permeabilized GH3 cells. 285 Jul 92

The breakdown of polyphosphoinositides (PPI) but not phosphatidylinositol (PI) has been hypothesized as the primary event following agonist (hormones/growth factors/neurotransmitters) stimulation in a wide variety of systems. This, in turn, predicts the existence of a phospholipase C (PLC) enzyme that shows specificity to PPI. Ideally, this PPI-specific PLC activity should not be absolutely dependent on Ca2+ because of its proposed role in Ca2+ mobilization. I have recently identified two PLC activities that are specific to PPI and have described their resolution from a PLC that acts on all three phosphoinositides (Manne, 1987). In this report, I describe purification to near homogeneity of one of these PLC activities. The enzyme shows maximal activity towards PPI in the presence of physiological Mg2+ concentrations, and does not act on PI under conditions optimal for PPI hydrolysis. However, a weak PI hydrolytic activity, representing about 1/8th to 1/20th of that observed with PPI is detected when 0-100 microM Ca2+ is present in the assay. This weak PI hydrolytic activity is strongly inhibited by mM Ca2+, which is required at mM levels for most of the PLC enzymes described in literature. The size of the native enzyme as determined by gel filtration (high performance liquid chromatography) is 140 kDa. Analysis of the purified enzyme by HPLC on Zorbax GF-250 column showed a single major peak that coincided with the enzyme activity. Under both denaturing and non-denaturing conditions of SDS-polyacrylamide gel electrophoresis, the highly purified enzyme shows two major bands of 38 kDa and 42 kDa, which together represent about 90% of the total stain on the gel.
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PMID:A novel candidate for receptor-coupled phospholipase C purified from human platelets. 285 55

Rat pheochromocytoma cells (PC12) permeabilized with staphylococcal alpha-toxin release [3H]dopamine after addition of micromolar Ca2+. This does not require additional Mg2+-ATP (in contrast to bovine adrenal medullary chromaffin cells). We also observed Ca2+-dependent [3H]-dopamine release from digitonin-permeabilized PC12 cells. Permeabilization with alpha-toxin or digitonin and stimulation of the cells were done consecutively to wash out endogenous Mg2+-ATP. During permeabilization, ATP was removed effectively from the cytoplasm by both agents but the cells released [3H]dopamine in response to micromolar Ca2+ alone. Replacement by chloride of glutamate, which could sustain mitochondrial ATP production in permeabilized cells, does not significantly alter catecholamine release induced by Ca2+. However, Mg2+ without ATP augments the Ca2+-induced release. The release was unaltered by thiol-, hydroxyl-, or calmodulin-interfering substances. Thus Mg2+-ATP, calmodulin, or proteins containing -SH or -OH groups are not necessary for exocytosis in permeabilized PC12 cells.
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PMID:Further characterization of dopamine release by permeabilized PC12 cells. 288 54

The phospholipid requirement for Ca2+-stimulated, Mg2+-dependent ATP hydrolysis (Ca2+/Mg2+-ATPase) and Mg2+-stimulated ATP hydrolysis (Mg2+-ATPase) in rat brain synaptosomal membranes was studied employing partial delipidation of the membranes with phospholipase A2 (Hog pancreas), phospholipase C (Bacillus cereus) and phospholipase D (cabbage). Treatment with phospholipase A2 caused an increase in the activities of both Ca2+/Mg2+-ATPase and Mg2+-ATPase whereas with phospholipase C treatment both the enzyme activities were inhibited. Phospholipase D treatment had no effect on Ca2+/Mg2+-ATPase but Mg2+-ATPase activity was inhibited. Inhibition of Mg2+-ATPase activity after phospholipase C treatment was relieved with the addition of phosphatidylinositol-4,5-bisphosphate (PIP2) and to a lesser extent with phosphatidylinositol-4-phosphate (PIP) and phosphatidylcholine (PC). Phosphatidylserine (PS), phosphatidic acid (PA), PIP and PIP2 brought about the reactivation of Ca2+/Mg2+-ATPase. Phosphatidylinositol (PI) and PA inhibited Mg2+-ATPase activity. Kms for Ca2+ (0.47 microM) and Mg2+ (60 microM) of the enzyme were found to be unaffected after treatment with the phospholipases.
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PMID:Phospholipid requirement of Ca2+-stimulated, Mg2+-dependent ATP hydrolysis in rat brain synaptic membranes. 294 70


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