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)

GTP-binding proteins have been implicated to function as key transducing elements in the mechanism underlying receptor activation of a membrane-associated phospholipase C activity. In the present study, the regulation of phospholipase C activity by GTP-binding proteins has been characterized in a detergent-solubilized system derived from bovine brain membranes. Guanosine-5'-(3-O-thio)triphosphate (GTP-gamma-S) and guanyl-5'-yl imidodiphosphate (Gpp(NH)p) stimulated a dose-dependent increase in phospholipase C activity with half-maximal activation at 0.6 microM and 10 microM, respectively. The maximal degree of stimulation due to Gpp(NH)p or GTP-gamma-S was comparable. 100 microM GTP had only a slight stimulatory effect on phospholipase C activity. Adenine nucleotides, 100 microM adenylyl-imidodiphosphate and ATP, did not stimulate phospholipase C activity, indicating that specific guanine nucleotide-dependent regulation of phospholipase C activity was preserved in the solubilized state. Gpp(NH)p or GTP-gamma-S stimulation of phospholipase C activity was time-dependent and required Mg2+.Mg2+ regulated the time course for activation of phospholipase C by guanine nucleotides and the ability of guanine nucleotides to promote an increase in the Ca2+ sensitivity of phospholipase C. 200 microM GDP-beta-S or 5 mM EDTA rapidly reversed the activation due to GTP-gamma-S or Gpp(NH)p. These findings demonstrate that G protein regulation of phospholipase C activity in a bovine brain membrane- solubilized system occurs through a Mg2+ and time-dependent mechanism. Activation is readily reversible upon addition of excess GDP-beta-S or removal of Mg2+.
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PMID:G protein regulation of phospholipase C activity in a membrane-solubilized system occurs through a Mg2(+)- and time-dependent mechanism. 200 26

Choline, betaine and N,N-dimethylglycine as the sole carbon and nitrogen source induced a periplasmic acid phosphatase activity in Pseudomonas aeruginosa. This enzyme produced the highest rates of hydrolysis in phosphorylcholine and phosphorylethanolamine among the various phosphoric esters tested. At saturating concentrations of Mg2+, the Km values were 0.2 and 0.7 mM for phosphorylcholine and phosphorylethanolamine respectively. At high concentrations both compounds were inhibitors of the enzyme activity. The Ksi values for phosphorylcholine and phosphorylethanolamine were 1.0 and 3.0 mM respectively. The higher catalytic efficiency was that of phosphorylcholine. Considering these results it is possible to suggest that the Pseudomonas aeruginosa acid phosphatase is a phosphorylcholine phosphatase. The existence of this activity which is induced jointly with phospholipase C by different choline metabolites, in a high phosphate medium, suggests that the attack of Pseudomonas aeruginosa on the cell host may also be produced under conditions of high phosphate concentrations, when the alkaline phosphatase is absent.
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PMID:Identification of the Pseudomonas aeruginosa acid phosphatase as a phosphorylcholine phosphatase activity. 211 92

Of the total of 306 amino acids in the sequence of sphingomyelinase (SMPLC) from Bacillus cereus, almost half (150) are expected to be involved in the formation of loop or turn structure, while 65 and 73 residues may participate in the formation of alpha-helix and beta-structure, respectively. The helix content of SMPLC was calculated to be 0-5%, based on the CD spectra. The addition of divalent metal ions such as Mg2+ or both Ca2+ and Mg2+ had no effect on the CD spectra of SMPLC, although the addition of these metal ions caused the breakdown of membranous SM and specific adsorption of SMPLC onto erythrocyte membranes. A hydropathy study showed that SMPLC has hydrophobic regions at the N-terminal domain which must be responsible for the binding of the enzyme to the membranes. The partial homologies between the amino acid sequences of SMPLC and Clostridium perfringens alpha-toxin (phospholipase C) are discussed.
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PMID:Secondary structure of sphingomyelinase from Bacillus cereus. 212 32

Phosphatidylinositol 4-phosphate (PIP) kinase (E.C. 2.7.1.68) has been purified about 1200-fold from rat liver plasma membranes, taking advantage of affinity chromatography on quercetin-Sepharose as a novel step. The purified PIP kinase showed no contamination by the following enzyme activities: phosphatidylinositol (PI) kinase (EC 2.7.1.67), protein kinase C (EC 2.7.1.-), diacylglycerol kinase (EC 2.7.1.-), phospholipase C (EC 3.1.4.11), protein-tyrosine kinase (EC 2.7.1.112), alkaline phosphatase (EC 3.1.3.1), triphosphoinositide phosphomonoesterase (EC 3.1.3.36), adenylate kinase (EC 2.7.4.3) and cAMP-dependent protein kinase (EC 2.7.1.37). The liver membrane enzyme requires high Mg2+ concentrations with a KM value of 10 mM. Ca2+ or Mn2+ could replace Mg2+ to a certain, though small, extent. Apparent KM values with respect to PIP and ATP were 10 and 65 microM, respectively. GTP was slightly utilized by the kinase as phosphate donor while CTP was not. Quercetin inhibited the enzyme with Ki = 34 microM. Extending our previous observations (Urumow, T. and Wieland, O.H. (1986) FEBS Lett. 207, 253-257 and Urumow, T. and Wieland, O.H. (1988) Biochim. Biophys. Acta 972, 232-238) [gamma S]pppG still stimulated the PIP kinase in extracts of solubilized liver membranes. 20-40% (NH4)2SO4 precipitation of the membrane extracts yielded a fraction that contained the bulk of enzyme activity but did not respond to stimulation by [gamma S]pppG any longer. This was restored by recombination with a protein fraction collected at 40-70% (NH4)2SO4 saturation, presumably containing a GTP binding protein and/or some other factor separated from the PIP kinase. In the reconstituted system [gamma S]pppG stimulated PIP kinase in a concentration dependent manner with maximal activation at 5 microM. This effect was not mimicked by [gamma S]pppA and was blocked by [beta S]ppG. These results strongly support our view that in liver membranes PIP kinase is regulated by a G-protein.
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PMID:Purification and partial characterization of phosphatidylinositol-4-phosphate kinase from rat liver plasma membranes. Further evidence for a stimulatory G-protein. 215 97

The phosphoinositide-specific phospholipase C (PLC) activity present in the soluble and sarcolemmal enriched membrane fraction from guinea pig hearts was characterized using phosphatidyl [3H]inositol 4,5-biphosphate (PIP2) or phosphatidyl [3H]inositol 4-monophosphate (PIP) as substrates. The PLC activities (cytosolic and membrane associated) were specific for polyphosphoinositides (PIP2 and PIP) since no other phospholipids were hydrolyzed at pH 7.0 under various ionic conditions. Both enzymic activities were Ca2(+)-dependent (half maximal activities were achieved around pCa 5.0). The pH, detergent (deoxycholate), divalent (Ca2+ and Mg2+), and monovalent (Na+ and K+) cation dependencies were very similar between the cytosolic and membrane-associated enzyme activities, using either PIP2 or PIP as substrate. Hydrolysis of the polyphosphoinositides was inhibited in the presence of phosphatidylethanolamine, phosphatidylserine, or phosphatidylcholine. Under optimal conditions (pH 7.0, 1 mM Ca2+, 2.5 mM Mg2+, 100 mM Na+ and 0.07% deoxycholate) the specific activities of the cytosolic and membrane-associated enzymes were 19.9 +/- 0.9 and 10.1 +/- 0.9 nmol/min/mg protein, respectively, using PIP2 as substrate. Under the same conditions these activities were 18.1 +/- 1.0 and 8.0 +/- 0.8 nmol/min/mg protein for the cytosolic and membrane fractions, respectively, using PIP as substrate. Based on the similarity of the characteristics of these two PLC enzyme activities, it is suggested that the cytosolic and membrane-associated enzyme forms may be closely related.
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PMID:Characterization of cytoplasmic and membrane-associated phosphatidylinositol 4,5-biphosphate phospholipase C activities in guinea pig ventricles. 215 98

Membranes isolated from normal murine B lymphocytes were found to contain a novel phosphatidylinositol (PtdIns)-specific phospholipase C (PLC) which becomes activated as the Mg2+ concentration is raised from 30 to 1000 microM. This activity, which has not been described previously in any tissue, is restricted to naturally occurring B cell blasts, i.e. it was not detected in quiescent B cells, B lymphomas, or plasmacytomas. As seen in other cell systems, B cell membranes were found to contain Mg2(+)-stimulated inositol 1,4,5-trisphosphate phosphatase activity. Although neither the inositol 1,4,5-trisphosphate phosphatase nor the PtdIns PLC activities were affected by Ca2+, B cell membranes were found to contain a Ca2(+)-stimulated phosphatidylinositol 4,5-bisphosphate (PtdInsP2) PLC activity which is activated by [Ca2+] greater than 100 nM. Based on several characteristics, it appears that the Mg2(+)- and Ca2(+)-regulated PLCs are distinct species. First, they have distinct specificity for PtdIns and PtdInsP2, respectively. Second, they have distinct tissue distribution while the Ca2(+)-regulated activity was detected in all B cells, the Mg2(+)-regulated activity is restricted to low density, natural B blasts. Third, the kinetics of activation of the enzymes is distinct; the Mg2(+)-regulated enzyme exhibits slower and less transient activation kinetics. Fourth, the activities exhibit absolute specificity in terms of activation by Mg2+ and Ca2+, i.e. the PtdIns PLC is activated only by Mg2+ and the PtdInsP2 PLC is activated only by Ca2+. Data are consistent with the possibility that Mg2+ mobilization which follows ligation of certain receptors, may play an important role in the regulation of levels of the second messenger diacylglycerol.
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PMID:Divalent cation regulation of phosphoinositide metabolism. Naturally occurring B lymphoblasts contain a Mg2(+)-regulated phosphatidylinositol-specific phospholipase C. 216 Sep 65

Preparations of rod outer segments from cattle retinas contained soluble and particulate phospholipase C activities which hydrolyzed phosphatidylinositol 4,5-bisphosphate (PIP2) and the other phosphoinositides. Ca2+ was required for PIP2 hydrolysis, but high (greater than 300 microM) concentrations were inhibitory. Mg2+ and spermine at low concentrations stimulated the particulate activity but inhibited the soluble. Mn2+ inhibited both. High (greater than 100 microM) concentrations of the nonhydrolyzable GTP analogue guanylyl beta,gamma-methylenediphosphonate inhibited PIP2 hydrolysis by both the soluble and particulate activities, but guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), fluoride, and cholera and pertussis toxins were without effect. Overall phospholipase C activity in ROS was unaffected by light. Evidence was found for multiple forms of the enzyme, requiring isolation and separate characterization before ruling out regulation by light or G-protein.
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PMID:Phosphatidylinositol-4,5-bisphosphate phospholipase C in bovine rod outer segments. 216 27

In [3H]inositol-labeled membranes prepared from Swiss mouse 3T3 and human small cell lung carcinoma cells, [Tyr4]-bombesin stimulated production of water-soluble inositol phosphates. The reaction was stimulated by guanosine 5'-O-[3-thiotriphosphate] and was specifically inhibited by both [Leu13-psi-CH2NHLeu14]-bombesin and the antibombesin antibody 2A11. [Tyr4]-bombesin-induced activation of phospholipase C is most apparent in Ca2(+)-depleted conditions (less than 1 microM[Ca2+]free). The kinetics of activation by ligand also demonstrate that [Tyr4]-bombesin-dependent phospholipase C activation is most apparent at [Mg2+]free of approximately 0.2 microM. At millimolar concentrations of [Mg2+]free, there is considerably less dependence on [Tyr4]-bombesin for activation of phospholipase C. ATP is not necessary for initial activation of phospholipase C, and beta, gamma-imidoadenosine-5'-triphosphate does not inhibit the reaction. These results demonstrate that in these cell types [Tyr4]-bombesin activates phospholipase C in conjunction with guanine nucleotides. Phospholipase C-coupled guanine nucleotide regulatory proteins would be appropriately considered as novel targets for the development of therapeutic strategies in small cell lung carcinoma.
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PMID:Effect of guanine and adenine nucleotides on bombesin-stimulated phospholipase C activity in membranes from Swiss 3T3 and small cell lung carcinoma cells. 216 51

The interaction of Staphylococcus aureus alpha-toxin with planar lipid membranes results in the formation of ionic channels whose conductance can be directly measured in voltage-clamp experiments. Single-channel conductance depends linearly on the solution conductivity suggesting that the pores are filled with aqueous solution; a rough diameter of 11.4 +/- 0.4 A can be estimated for the pore. The conductance depends asymmetrically on voltage and it is slightly anion selective at pH 7.0, which implies that the channels are asymmetrically oriented into the bilayer and that ion motion is restricted at least in a region of the pore. The pores are usually open in a KCl solution but undergo a dose- and voltage-dependent inactivation in the presence of di- and trivalent cations, which is mediated by open-closed fluctuations at the single-channel level. Hill plots indicate that each channel can bind two to three inactivating cations. The inhibiting efficiency follows the sequence Zn2+ greater than Tb3+ greater than Ca2+ greater than Mg2+ greater than Ba2+, suggesting that carboxyl groups of the protein may be involved in the binding step. A voltage-gated inactivation mechanism is proposed which involves the binding of two polyvalent cations to the channel, one in the open and one in the closed configuration, and which can explain voltage, dose and time dependence of the inactivation.
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PMID:Ionic channels formed by Staphylococcus aureus alpha-toxin: voltage-dependent inhibition by divalent and trivalent cations. 242 95

Rat mast cells and bone marrow-derived mouse mast cells (BMMC) were sensitized with mouse IgE mAb, and permeabilized by ATP to introduce guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S) and/or guanosine-5'-O-(2-thiodiphosphate) (GDP beta S) into the cells. After ATP-induced lesions were resealed with Mg2+, the cells were challenged by Ag to determine the effect of the nonhydrolyzable guanosine phosphate on Ag-induced hydrolysis of phosphoinositides and histamine release. Introduction of GTP gamma S into permeabilized rat mast cells or BMMC, followed by exposure of the cells to extracellular Ca2+, resulted in histamine release, but failed to induce hydrolysis of phosphoinositides. It was also found that introduction of GTP gamma S into the cells did not synergistically enhance Ag-induced histamine release. Introduction of GDP beta S into sensitized BMMC inhibited the GTP gamma S-dependent, Ca2+-induced histamine release but failed to inhibit Ag-induced histamine release. The results suggest that GTP gamma S-dependent, Ca2+-induced histamine release and Ag-induced histamine release go through independent biochemical pathways. It was also found that introduction of GTP gamma S or GDP beta S into sensitized BMMC neither enhanced nor inhibited Ag-induced formation of inositol phosphates. These results together with previous findings that pretreatment of BMMC with either pertussis toxin or cholera toxin does not affect Ag-induced hydrolysis of phosphoinositides, indicate that a G protein is not involved in the transduction of IgE-mediated triggering signals to phospholipase C in rodent mast cells.
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PMID:Effect of nonhydrolyzable guanosine phosphate on IgE-mediated activation of phospholipase C and histamine release from rodent mast cells. 247 37


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