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PubMed1995

Thyrotropin-induced hydrogen peroxide production in FRTL-5 thyroid cells is mediated not by adenosine 3',5'-monophosphate, but by Ca2+ signaling followed by phospholipase-A2 activation and potentiated by an adenosine derivative.

The production of hydrogen peroxide (H2O2) as an essential process for iodide organification is a key reaction in TSH-induced thyroid hormone synthesis. Here we characterize the signal transduction pathway involved in TSH-induced H2O2 production in FRTL-5 thyroid cells. At higher than 1 nM TSH, N6-(L-2-phenylisopropyl)adenosine (PIA), an adenosine receptor agonist having, by itself, no influence on H2O2 generation, potentiated this TSH action, whereas the TSH increase and PIA addition reduced cAMP accumulation. RO 20-1724, a phosphodiesterase inhibitor, amplified the TSH-induced cAMP accumulation, but did not change H2O2 generation in the whole range of TSH used. Ca(2+)-mobilizing agonists, GTP and ATP, also induced H2O2 production without stimulating cAMP accumulation. Chelation of intracellular Ca2+ markedly inhibited the TSH action, but intracellular Ca2+ increases by either thapsigargin or ionomycin mimicking it. All of the findings show the participation of Ca2+, but not cAMP, in the action of TSH. Desensitization of protein kinase-C (PKC) did not influence the receptor-mediated H2O2 production, suggesting the reduced importance of PKC activation compared to Ca2+ signaling to the reaction. A rise in intracellular Ca2+ independent of receptor activation also induced H2O2 production as well as arachidonate release, and both were potentiated by PIA. In addition, inhibitors of phospholipase-A2 and the arachidonate metabolic pathway depressed H2O2 generation, suggesting the participation of an arachidonate cascade in the Ca(2+)-dependent H2O2 production. Lipoxygenase inhibitors depressed the Ca2+ action without influencing arachidonate release, suggesting the involvement of a lipoxygenase product(s) of arachidonate in the Ca(2+)-signaling mechanism. In conclusion, in FRTL-5 cells, TSH-induced H2O2 production is mediated not by cAMP, but by the phospholipase-C/Ca2+ cascade, possibly followed by the Ca(2+)-dependent phospholipase-A2/arachidonate cascade. PIA amplifies TSH-induced H2O2 production at the steps of phospholipase-C and phospholipase-A2 activation in a pertussis toxin-sensitive manner.

Adenosine↗
PubMed1997

Release of ectoenzymes from small intestine brush border membranes of mice by phospholipases.

This study investigated ectoenzyme release from small intestine brush border membranes (duodenum and jejunum, Preparation A; ileum, Preparation B) of mice by the action of phosphatidylinositol-specific phospholipase C or glycosyl-phosphatidylinositol-specific phospholipase D. Most of the alkaline phosphatase was solubilized from Preparation A, but about 60% was released from Preparation B. As for alkaline phosphodiesterase I activity, 15 and 10% were released from Preparations A and B, respectively. With Preparation B, octylglucoside treatment followed by phosphatidylinositol-specific phospholipase C or glycosyl-phosphatidylinositol-specific phospholipase D completely solubilized the alkaline phosphatase activity. However, this treatment did not change the ratio of release of alkaline phosphodiesterase I from Preparation A or B. These results indicate that the resistance to alkaline phosphatase found in Preparation B is due to hindered accessibility of the bonding splitting by phosphatidylinositol-specific phospholipase C and not to a modified glycosyl-phosphatidylinositolanchor.

Alkaline Phosphatase↗
PubMed1996

Phospholipase A2 is involved in the mechanism of activation of neutrophils by polychlorinated biphenyls.

Aroclor 1242, a mixture of polychlorinated biphenyls (PCBs), activates neutrophils to produce superoxide anion (O2-) by a mechanism that involves phospholipase C-dependent hydrolysis of membrane phosphoinositides; however, subsequent signal transduction mechanisms are unknown. We undertook this study to determine whether phospholipase A2-dependent release of arachidonic acid is involved in PCB-induced O2- production. We measured O2- production in vitro in glycogen-elicited, rat neutrophils in the presence and absence of the inhibitors of phospholipase A2: quinacrine, 4-bromophenacyl bromide (BPB), and manoalide. All three agents significantly decreased the amount of O2- detected during stimulation of neutrophils with Aroclor 1242. Similar inhibition occurred when neutrophils were activated with the classical stimuli, formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate. The effects of BPB and manoalide were not a result of cytotoxicity or other nonspecific effects, although data suggest that quinacrine is an O2- scavenger. Significant release of 3H-arachidonic acid preceded O2- production in neutrophils stimulated with Aroclor 1242 or fMLP. Manoalide, at a concentration that abolished O2- production, also inhibited the release of 3H-arachidonate. Aspirin, zileuton, or WEB 2086 did not affect Aroclor 1242-induced O2- production, suggesting that eicosanoids and platelet-activating factor are not needed for neutrophil activation by PCBs. Activation of phospholipase A2 and O2- production do not appear to involve the Ah receptor because a congener with low affinity, but not one with high affinity for this receptor, stimulated the release of arachidonic acid and O2-. These data suggest that Aroclor 1242 stimulates neutrophils to produce O2- by a mechanism that involves phospholipase A2-dependent release of arachidonic acid.

Animals↗
PubMed1990

The crystal structure of a lysine 49 phospholipase A2 from the venom of the cottonmouth snake at 2.0-A resolution.

The crystal structure of a lysine 49 variant phospholipase A2 (K49 PLA2) has been determined at 2.0-A resolution. This particular phospholipase A2, purified from the venom of the eastern cottonmouth (Agkistrodon piscivorus piscivorus), a North American pit viper, differs significantly from others studied crystallographically because of replacement of the aspartate residue at position 49, whose side chain is important in calcium binding, by lysine. The crystallographic analysis of K49 PLA2 was undertaken to assess the structural ramifications of this substitution, particularly as they affect the binding mechanism of both the calcium cofactor and the phospholipid substrate. The protein crystals are tetragonal, space group P4(1)2(1)2, with unit cell dimensions of a = b = 71.7 (1) and c = 57.8 (3) A. Preliminary phases were obtained by molecular replacement techniques with a search model derived from the refined 2.5-A structure of a rattle-snake venom phospholipase A2 (Brunie, S., Bolin, J., Gewirth, D., and Sigler, P. B. (1985) J. Biol. Chem. 260, 9742-9749). The starting model gave an initial crystallographic RF of 0.526 (RF = sigma parallel to Fo /-/ Fc parallel to /sigma/Fo/). The structure was refined against all data to 2.0-A resolution. The final RF is 0.158. The final model includes 150 discrete water molecules. The K49 PLA2 model is composed primarily of alpha-helices joined by loops, some of which are quite extensive. Although dissimilarities are observed in the loop regions, the helical portions are very similar to those in other known phospholipase A2 structures. The proposed catalytic center (His48, Tyr73, and Asp99) is also structurally conserved. The region in K49 PLA2 corresponding to the calcium-binding site in other phospholipases A2 is occupied by the epsilon-amino group of lysine 49.

Amino Acid Sequence↗
PubMedDate not supplied

Involvement of a pertussis toxin-sensitive G protein-coupled phospholipase A2 in agonist-stimulated arachidonic acid release in membranes isolated from bovine iris sphincter smooth muscle.

We have shown that in bovine iris sphincter membranes G proteins are involved in coupling muscarinic-, PGF2 alpha-, endothelin- and platelet-activating factor receptors to the activation of phospholipase A2 and the release of arachidonic acid. GTP gamma S and GTP gamma S plus carbachol stimulated arachidonic acid release in the membranes in a dose- and time-dependent manner. Nucleotide stimulation was specific to GTP gamma S, since GDP, GDP beta S and ATP had no effect. The stimulatory effect of GTP gamma S plus carbachol was blocked by atropine and it required the presence of physiological concentrations of Ca2-. AIF4-, which bypasses the receptor and directly activates the G protein, induced arachidonic acid liberation in the intact iris sphincter, but was ineffective in the membranes. Addition of GTP gamma S plus carbachol to sphincter muscle membranes prelabeled with [3H]inositol or 3H-arachidonic acid resulted in the formation of lysophosphatidylinositol and the liberation of arachidonic acid, thus suggesting the involvement of phospholipase A2. In vitro treatment of the iris membranes with pertussis toxic inhibited arachidonic acid release by the agonists. This is in contrast to the pertussis toxin-insensitive G protein that activates phospholipase C in this tissue (22). These data demonstrate that in the iris sphincter a G protein is involved in the step between receptor activation and the activation of phospholipase A2, and that arachidonic acid release in this tissue is mediated by a pertussis-toxin-sensitive G protein-coupled phospholipase A2. Thus, GTP can regulate arachidonic acid release and its subsequent conversion into eicosanoids by stimulating its formation.

Aluminum↗
PubMed1992

Cinatrins, a novel family of phospholipase A2 inhibitors. II. Biological activities.

Cinatrins A, B and C3 inhibited phospholipase A2 purified from rat platelets in a dose-dependent manner. Cinatrin C3, the most potent component (IC50 70 microM), was noncompetitive with a Ki value of 36 microM. Cinatrins B and C3 also inhibited both porcine pancreas and Naja naja venom phospholipase A2. Inhibition of rat platelet phospholipase A2 by cinatrin C3 was independent of Ca2+ and substrate concentration. Comparison with duramycin, another phospholipase A2 inhibitor, displayed inhibition dependent on substrate concentration when phosphatidylethanolamine was the substrate. These results indicate that the inhibition of phospholipase A2 by cinatrin C3 may result from direct interaction with the enzyme.

Animals↗
PubMedDate not supplied

Validation of a method for determination of phospholipase A2 and melittin in bee venom preparations by capillary electrophoresis.

A method was validated for the determination of the 2 main components of bee venom, phospholipase A2 and melittin, by capillary electrophesis (CE). Optimum resolution and selectivity were attained with a running electrolyte of 150 mM phosphoric acid, pH 1.8. The repeatability and day-to-day reproducibility of the migration times were better than 0.36 and 2.8%, respectively. The repeatability and day-to-day reproducibility of the normalized peak areas were better than 1.3 and 2.6%, respectively. The response of the UV detector at 190 nm was linear over < 2 concentration decades, from 0.05 to 1.5 mg/mL, with correlation coefficients of 0.9994 for phospholipase A2 and 0.9997 for melittin. The limits of detection and quantitation were 4.5 and 15 microg/mL, respectively, for phospholipase A2 and 1.6 and 6 microg/mL, respectively, for melittin. The reproducibility of the measurements with 2 different CE instruments was satisfactory; the mean concentration and relative standard deviation (RSD) values for phospholipase A2 and melittin were 14.4% (RSD, 1.3%) and 51.4% (RSD, 1.1%), respectively, with instrument I; the corresponding values with instrument II were 14.5% (RSD, 2.8%) and 52.3% (RSD, 2.2%). The accuracy was estimated by comparison with a liquid chromatographic (LC) method. Differences between the CE and LC measurements were attributed to irreversible adsorption of the analytes on the LC column. The recoveries of phospholipase A2 and melittin with the CE method were 98.8 and 101.7%, respectively.

Bee Venoms↗
PubMed2001

Lack of association between schizophrenia and the phospholipase-A(2) genes cPLA2 and sPLA2.

The well-established role of genetic factors in the etiology of schizophrenia together with reports of allelic association with cPLA2, a phospholipase-A(2) gene, a reported increase of phospholipase-A(2) activity, and the phospholipase-A(2) hypothesis of Horrobin et al. [1995: Med Hypotheses 45:605-613] strongly support cPLA2 (PLA2G4A) and sPLA2 (PLA2G1B) as candidate genes for schizophrenia. In search for allelic association between these phospholipase-A(2) genes and schizophrenia, two samples of Chinese and European origins, in total 328 unrelated schizophrenic patients and their parents, were investigated using Falk and Rubinstein's haplotype relative risk method. Both genes showed marginally significant evidence for association in the total sample (P <or= 0.05), which, however, did not survive the Bonferroni correction for multiple testing. In conclusion, our results do not provide support for the phospholipase-A(2) hypothesis of schizophrenia. Additional studies will be necessary to rule out a possible confounding effect of niacin sensitivity as postulated by Hudson et al. [1999: Biol Psychiatr 46:401-405].

Adolescent↗
PubMed1992

Equal inhibition of HIV replication by stereoisomers of phosphatidyl-azidothymidine. Lack of stereospecificity of lysosomal phospholipase A1.

Glycerol-1-P and glycerol-3-P stereoisomers of dipalmitoylphosphatidylazidothymidine were synthesized and found to have equal antiretroviral activity in HIV-infected HT4-6C cells. It was anticipated that the glycerol-1-P isomer would be less active because of slow metabolic conversion by cellular phospholipases A and C, but the antiretroviral results suggested that the human cell line (HT4-6C) may have phospholipases capable of hydrolyzing 2,3-dipalmitoyl-sn-glycerol-1-phospho-5'-azidothymidine (AZT). To evaluate this possibility, we purified lysosomal phospholipase A1, an enzyme known to play a major role in cellular phospholipid catabolism. This enzyme rapidly hydrolyzed both the sn-1 and sn-3 isomers of dipalmitoylphosphatidyl-AZT. We synthesized sn-2,3-dipalmitoyl-glycero-1-phosphocholine and found that it is also hydrolyzed readily by lysosomal phospholipase A1 although the Vmax, 59 mumol mg-1 h-1, is slightly lower than that of the sn-1,2-dipalmitoyl-glycero-3-phosphocholine, 89 mumol mg-1 h-1. In conclusion, our studies show that sn-2,3-dipalmitoyl-glycerol-1-phospho-AZT is equal in antiviral activity to sn-1,2-dipalmitoyl-glycero-3-phospho-AZT in HIV-infected HT4-6C cells. This surprising result is due in part to the lack of stereospecificity of lysosomal phospholipase A1.

Animals↗
PubMed1990

Phospholipase A production by isolates of Salmonella species.

The incidence of intra- and extra-cellular phospholipase-A production by Salmonella isolates from human, poultry and environmental material was investigated. Nearly 17 per cent (15/90) of the strains tested produced phospholipase A. Phospholipase production was encountered in S. typhi, S. paratyphi A, S. typhimurium, S. seftenberg, S. bareilly, S. weltevredeen, S. newport, S. adelaide, S. alachua and S. gallinarum. Maximum (10/15) phospholipase producers were isolated from the human material. Phospholipase positive human isolates exhibited a high incidence of simultaneous multiple drug resistance, enterotoxigenicity and cell surface hydrophobicity.

Animals↗
PubMedDate not supplied

Phospholipase A2 activity in platelets. Immuno-purification and localization of the enzyme in rat platelets.

A comparative study on phospholipase A2 activity in platelet lysates from various species was carried out using identical assay conditions with phosphatidylethanolamine as substrate. Platelet phospholipase A2, both when expressed as activity per ml blood and as specific activity in KCl extracts, was low in human, cow, pig and goat. Moderate activities, in increasing order, were found in sheep, horse and rabbit, while rats showed by far the highest activity. In the latter four species total lysate activity was recovered in 1 M KCl extracts, suggesting that the enzyme occurs either in soluble form or as a peripheral membrane-associated protein. Immune cross-reactivity with monoclonal antibodies against rat liver mitochondrial phospholipase A2 was studied in dot-blot and monoclonal antibody-Sepharose binding experiments. Only sheep and rat platelet extracts contained cross-reactive phospholipase(s) A2. Immuno-affinity chromatography of rat platelet extracts indicated virtually complete binding of total phospholipase A2 activity and yielded pure enzyme in a single purification step. Enzyme visualization by immunogold electron microscopy showed a predominant localization in the matrix of alpha-granules.

Animals↗
PubMed1984

Stimulation of Na+-Ca2+ exchange in cardiac sarcolemmal vesicles by phospholipase D.

Treatment of canine cardiac sarcolemmal vesicles with phospholipase D resulted in a large stimulation (up to 400%) of Na+-Ca2+ exchange activity. The phospholipase D treatment decreased the apparent Km (Ca2+) for the initial rate of Nai+-dependent Ca2+ uptake from 18.2 +/- 2.6 to 6.3 +/- 0.3 microM. The Vmax increased from 18.0 +/- 3.6 to 31.5 +/- 3.6 nmol of Ca2+/mg of protein/s. The effect was specific for Na+-Ca2+ exchange; other sarcolemmal transport enzymes ((Na+, K+)-ATPase; ATP-dependent Ca2+ transport) are inhibited by incubation with phospholipase D. Phospholipase D had little effect on the passive Ca2+ permeability of the sarcolemmal vesicles. After treatment with 0.4 unit/ml of phospholipase D (20 min, 37 degrees C), the sarcolemmal content of phosphatidic acid rose from 0.9 +/- 0.2 to 8.9 +/- 0.4%; simultaneously, Na+-Ca2+ exchange activity increased 327 +/- 87%. It is probable that the elevated phosphatidic acid level is responsible for the enhanced Na+-Ca2+ exchange activity. In a previous study (Philipson, K. D., Frank, J. S., and Nishimoto, A. Y. (1983) J. Biol. Chem. 258, 5905-5910), we hypothesized that negatively charged phospholipids were important in Na+-Ca2+ exchange, and the present results are consistent with this hypothesis. Stimulation of Na+-Ca2+ exchange by phosphatidic acid may be important in explaining the Ca2+ influx which accompanies the phosphatidylinositol turnover response which occurs in a wide variety of tissues.

Animals↗
PubMed1981

Differential activation of platelet phospholipases by thrombin and ionophore A23187.

Although exposure of platelets to ionophore A23187 causes some activation of phospholipase C, ionophore is an inefficient stimulus for this enzyme. A23187 induces the formation of one-fourth to one-sixth as much diglyceride as does thrombin when comparable amounts of phosphatidylinositol are hydrolyzed. We have shown previously that in the presence of indomethacin thrombin-treated platelets accumulate significant quantitites of diglyceride via inhibition of diglyceride lipase. However, a similar accumulation of diglyceride does not occur when ionophore is used as a stimulus in the presence of indomethacin. Ionophore does not appear to be stimulating the catabolism of diglyceride, since the simultaneous addition of ionophore and thrombin does not impair the formation and metabolism of diglyceride which is promoted by thrombin alone. Further, whereas indomethacin exerts no inhibitory effects upon phospholipase C or the formation of diglyceride in platelets responding to either stimulus, indomethacin does inhibit 1) the loss of arachidonic acid from phosphatidylcholine in response to thrombin and 2) the loss of arachidonic acid from phosphatidylcholine and phosphatidylinositol in response to A23187. We conclude that in A23187-activated platelets, phosphatidylinositol is hydrolyzed primarily by an enzyme other than phospholipase C. This indomethacin-inhibitable enzyme is probably a phospholipase A. Therefore, the full expression of phospholipase C in platelets requires more than a general flux in intracellular calcium.

Anti-Bacterial Agents↗
PubMed1982

[Role of calcium ions in the development of the catalytic activity of phospholipase D].

The peculiarities of the reaction of mycellar lecithine cleavage by phospholipase D and the role of Ca2+ in the catalytic activity of the enzyme were studied. It was shown that Ca2+ participates in the formation of a catalytically active intermediary enzyme-substrate complex with a strict stoichiometric ratio of substrate, phospholipase activator (Na-DS) and Ca2+. The kinetics of inhibition for this reaction by lantane and fluoride ions and EDTA were studied. The inhibition of the reaction in a lecithine-Na-Ca2+-phospholipase D system by La3+ is due to substitution of bivalent Ca2+ by trivalent La3+ within the intermediary complex. The inhibiting effect of F- is due to penetration of the electron-negative ion into the coordination sphere of the intermediary complex and to disturbances in the hydrophobic binding between the ligands. The inhibitory action of EDTA is revealed during protein binding to the substrate and is not due to the chelating capacity of EDTA with respect to Ca2+. It was demonstrated that the role of Ca2+ is not restricted by its binding to phospholipase C. Ca2+ are also necessary for neutralization of the extra charge on the surface of substrate mycelles, production of an appropriate ionic strength and modification of the substrate phase surface at the interface. The catalytic function of Ca2+ consists in a formation of a "recognition" site in the active center of phospholipase D.

Calcium↗
PubMed1983

Effects of phospholipase C on the Na+-Ca2+ exchange and Ca2+ permeability of cardiac sarcolemmal vesicles.

We have examined the effects of phospholipase C pretreatment on Ca2+ transport in highly purified canine cardiac sarcolemmal vesicles. Na+-Ca2+ exchange, measured as Nai+-dependent Ca2+ uptake, is stimulated when 10-70% of the membrane phospholipid has been hydrolyzed. Although the phospholipase C treatment also increases sarcolemmal passive Ca2+ flux, the membrane maintains a sufficient permeability barrier for enhanced transport (via Na+-Ca2+ exchange) to be observed. These effects can be obtained with phospholipase C from either Clostridium perfringens or Bacillus cereus. We find that the phospholipase C (C. perfringens) preferentially hydrolyzes phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin leaving the negatively charged phospholipids, phosphatidylserine and phosphatidylinositol, intact. This suggests that the presence of negatively charged phospholipids is sufficient to ensure Na+-Ca2+ exchange activity. Thin section electron microscopy reveals gross morphological changes in phospholipase C-treated sarcolemma. The vesicles are aggregated and diacylglycerol droplets are visible. Fusion occurs such that adjacent vesicles share a common bilayer. It is surprising that vesicles displaying severe structural damage can demonstrate enhanced transport activity.

Animals↗
PubMed1981

Lack of correlation between anticoagulant activity and phospholipid hydrolysis by snake venom phospholipases A2.

The anticoagulant effects and the simultaneous plasma phospholipid hydrolysis induced by three purified phospholipases obtained from snake venoms, i.e., the basic, relatively toxic N. nigricollis, the neutral, relatively nontoxic H. haemachatus, and the acidic, relatively nontoxic N. n. atra, have been compared. The N. nigricollis phospholipase has a very strong anticoagulant effect at concentrations which induce relatively low levels of phospholipid hydrolysis in plasma. The H. haemachatus and N. n. atra phospholipases become anticoagulant only at high concentrations, and the associated phospholipid hydrolysis is also very high. It is concluded that, while all phospholipases are likely to inhibit coagulation if used in amounts sufficiently large to deplete plasma of phospholipids, strongly active phospholipases, such as N. nigricollis, interfere nonenzymatically with the clotting process before any appreciable phospholipid hydrolysis is reached.

Animals↗
PubMed1995

Agonist-mediated activation of phosphatidylcholine-specific phospholipase C and D in intestinal smooth muscle.

The contributions of phosphoinositide (PI)- and phosphatidylcholine (PC)-specific phospholipases [PI-specific phospholipase C (PI-PLC), PC-specific phospholipase C (PC-PLC), and phospholipase D (PLD)] to diacylglycerol (DAG) formation and regulation of the enzymes by G proteins, Ca2+, and protein kinase C (PKC) were examined in dispersed intestinal circular and longitudinal muscle cells. DAG formation induced by cholecystokinin was biphasic and paralleled by PKC activity. The initial phase (approximately 1 min) was mediated by PI-PLC in circular muscle cells and by both PI- and PC-PLC in longitudinal muscle cells, whereas the sustained phase was mediated by PC-PLC and PLD in both cell types. PC-PLC activity during the initial phase was identified by rapid formation of the initial products [3H]phosphocholine (5 sec) and [3H]myristate-labeled DAG (approximately 15 sec). PLD activity did not contribute to DAG formation during the initial phase, and PI hydrolysis had no effect on PC-PLC or PLD activity during the initial or sustained phases. PLD activity during the sustained phase was evident by the formation of [3H]phosphatidylethanol, a PLD-specific transphosphatidylation product. Dephosphorylation of phosphatidic acid (PA) by phosphatidate phosphohydrolase (PPH) accounted for about 50% of DAG formation; inhibition of PPH activity by propranolol or suppression of PA formation by ethanol inhibited DAG formation by 59-69% and 57-62%, respectively. Residual DAG in the presence of ethanol was augmented 55-57% by DAG kinase inhibitor, whereas residual PA was inhibited by 60-67%, implying that PA was derived from DAG, and DAG from PLC-mediated PC hydrolysis. In the presence of ethanol, calphostin C inhibited phosphatidylethanol formation but had no effect on PA or DAG levels, implying that only PLD activity was modulated by PKC. Maintenance of resting intracellular Ca2+ concentrations, rather than an agonist-induced increase in the intracellular Ca2+ concentration, was required for optimal PC-PLC and PLD activity. Guanosine-5'-O-(beta-thio)diphosphate abolished DAG and PA formation in reversibly permeabilized muscle cells. We conclude that DAG formation in intestinal muscle is mediated by time-dependent activation of three phospholipases (PI-PLC, PC-PLC, and PLD) and two converting enzymes (DAG kinase and PPH). PC-PLC and PLD are Ca2+ dependent and appear to be G protein coupled; only PLD is PKC sensitive.

Animals↗
PubMed1994

Solubilization of neuropathy target esterase and other phenyl valerate carboxylesterases from chicken embryonic brain by phospholipase A2.

Membrane-bound neuropathy target esterase (NTE) and associated phenyl valerate carboxylesterases were solubilized from chicken embryo brain by phospholipase A2. Phospholipase A2 from bee or cobra (Naja) venoms were the most effective preparations in solubilizing brain NTE and other phenyl valerate carboxylesterases. Phospholipase C and several proteinases (endoproteinase, pronase E, proteinase K, thermolysin, trypsin) did not solubilize brain membrane-bound carboxylesterases but reduced their activity. NTE solubilization by phospholipase A2 did not affect its apparent Km and Vmax for the substrate phenyl valerate or the susceptibility of phenyl valerate carboxylesterases to inhibition by paraoxon and mipafox. NTE thermal stability diminished after the treatment of brain membrane fragments with phospholipase A2.

Animals↗