Phosphatidylcholine Cholinephosphohydrolase Research Articles

Safety evaluation of the food enzyme phospholipase C from the genetically modified Bacillus licheniformis strain NZYM-VR.

The food enzyme phospholipase C (phosphatidylcholine cholinephosphohydrolase EC 3.1.4.3) is produced with the genetically modified Bacillus licheniformis strain NZYM‐VR by Novozymes A/S. The genetic modifications do not give rise to safety concerns. The food enzyme is free from viable cells of the production organism and its DNA. This phospholipase C is intended for use in degumming of fats and oils. The residual amounts of Total Organic Solids (TOS) are removed during washing and purification steps applied during degumming. Consequently, no dietary exposure was calculated. Genotoxicity tests did not raise a safety concern. The systemic toxicity was assessed by means of a repeated dose 90‐day oral toxicity study in rats. The Panel identified a No Observed Adverse Effect Level (NOAEL) at the highest dose tested of 714 mg TOS/kg body weight (bw) per day. Similarity of the amino acid sequence to those of known allergens was searched for and no match was found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood is considered to be low. Based on the data provided and the removal of TOS during the degumming of fats and oils, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

The prevalence of multidrug-resistant Aeromonas spp. in the municipal wastewater system and their dissemination in the environment

The objective of this study was to identify the determinants of antibiotic resistance and virulence of Aeromonas spp. isolated from treated wastewater (WW) and from samples of river water collected upstream (URW) and downstream (DRW) from the effluent discharge point. The resistance of Aeromonas spp. to antibiotics that are widely used in human and veterinary medicine, including beta-lactams, tetracyclines, glycylcyclines, fluoroquinolones, aminoglycosides and sulfamethoxazole-trimethoprim, was analyzed by disk diffusion method. The prevalence of hemolysins, aerolysins (virulence factors) and integrase genes was determined. A total of 83 Aeromonas spp. strains were selected from the isolates obtained from river water and wastewater samples. The highest percentage (81.8%) of multidrug-resistant isolates was noted in DRW samples. The analyzed isolates were most frequently resistant to beta-lactams, tetracyclines and aminoglycosides, whereas resistance to glycylcyclines was least common. Isolates resistant to beta-lactams most frequently harbored blaTEM and blaOXA genes. The group of genes encoding resistance to tetracyclines was most frequently represented by tet(E) and tet(O). Genes encoding virulence ahh1 (heat-labile hemolysin) or integrase intI1 occurred more frequently in the strains isolated from DRW than URW. An analysis of genetic relatedness revealed two main clusters – one with closely related WW and DRW isolates and one with less related isolates from all analyzed samples. The results of this study indicate that regardless of the applied treatment, municipal sewage may be a reservoir of antibiotic-resistant bacteria, antibiotic resistance and virulence genes and that treated water can contaminate other environmental domains.

Purification and characterization of enterotoxigenic El Tor-like hemolysin produced by Vibrio fluvialis.

The halophilic bacterium Vibrio fluvialis is an enteric pathogen that produces an extracellular hemolysin. This hemolysin was purified to homogeneity by using sequential hydrophobic-interaction chromatography with phenyl-Sepharose CL-4B and gel filtration with Sephacryl S-200. It has a molecular weight of 63,000 and an isoelectric point of 4.6, and its hemolytic activity is sensitive to heat, proteases, and preincubation with zinc ions. The hemolysin lyses erythrocytes of the eight different animal species that we tested, is cytotoxic against Chinese hamster ovary cells in tissue culture, and elicits fluid accumulation in suckling mice. Lysis of erythrocytes occurs by a temperature-dependent binding step followed by a temperature- and pH-dependent lytic step. Fourteen of the first 20 N-terminal amino acid residues (Val-Ser-Gly-Gly-Glu-Ala-Asn-Thr-Leu-Pro-His-Val-Ala-Phe-Tyr-Ile-Asn-Val-Asn-Arg) are identical to those of the El Tor hemolysin of Vibrio cholerae and the heat-labile hemolysin of Vibrio mimicus. This homology was further confirmed by PCR analysis using a 5' primer derived from the amino-terminal sequence of the hemolysin and a 3' primer derived from the El Tor hemolysin structural gene. The hemolysin also reacts with antibodies to the El Tor-like hemolysin of non-O1 V. cholerae.

Effect of Metal lons on Phospholipase C (Heat-Labile Hemolysin) from Pseudomonas aeruginosa

Phospholipase C (PLC; heat-labile hemolysin) was purified from Pseudomonas aeruginosa culture supernatants to near homogeneity by ion exchange chromatography. Some chelating reagents and divalent metal ions were examined for their effects on the purified PLC activity. EDTA, ECTA, and o-phenanthroline did not inhibit the enzyme activity to p-nitrophenylphosphorylcholine (pNPPC) at concentrations below 10 mmol/L. Inclubation with Zn2+, Cu2+, Co2+ or Ni2+ caused a decrease in the enzyme activity. The activity of EDTA-treated PLC was most remarkably decreased in the presence of Zn2+, followed in descending order by Cu2+, Co2+ and Ni2+, while other metal ions (Mg2+, Ca2+, Ba2+, and Mn2+) did not significantly affect the enzyme activity using concentrations up to 10 mmol/L. Zn2+ competitively inhibited the enzyme activity against pNPPC, with a Ki value of 0.3 mmol/L. The hemolytic activity of PLC was also completely inhibited in the presence of 1 mmol/L Zn2+, and inactivation of the enzyme by Zn2+ was not reversed by concomtitant addition of other divalent metal ions. These results suggest that hemolytic PLC from P. aeruginosa has a unique property in that there is no metal ion requirement for its activity. Phospholipase C (PLC; heat-labile hemolysin) was purified from Pseudomonas aeruginosa culture supernatants to near homogeneity by ion exchange chromatography. Some chelating reagents and divalent metal ions were examined for their effects on the purified PLC activity. EDTA, ECTA, and o-phenanthroline did not inhibit the enzyme activity to p-nitrophenylphosphorylcholine (pNPPC) at concentrations below 10 mmol/L. Inclubation with Zn2+, Cu2+, Co2+ or Ni2+ caused a decrease in the enzyme activity. The activity of EDTA-treated PLC was most remarkably decreased in the presence of Zn2+, followed in descending order by Cu2+, Co2+ and Ni2+, while other metal ions (Mg2+, Ca2+, Ba2+, and Mn2+) did not significantly affect the enzyme activity using concentrations up to 10 mmol/L. Zn2+ competitively inhibited the enzyme activity against pNPPC, with a Ki value of 0.3 mmol/L. The hemolytic activity of PLC was also completely inhibited in the presence of 1 mmol/L Zn2+, and inactivation of the enzyme by Zn2+ was not reversed by concomtitant addition of other divalent metal ions. These results suggest that hemolytic PLC from P. aeruginosa has a unique property in that there is no metal ion requirement for its activity.

Phospholipase C from Pseudomonas Fluorescens Strain B

ABSTRACTPhospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3.) was secreted in the culture supernatant by Pseudomonas fluorescens strain B. The maximum enzyme release was observed at the early stationary phase of culture growth. The most suitable medium for enzyme production was found to be casein soy broth containing additional 0.5% xylose and 1mM MgCh2. Phospholipase C from Pseudomonas fluorescens was purified 37 fold with 42% yield by a combination of ultrafiltration and Sephadex G75 column chromatography.

Effect of divalent cations on hemolysin synthesis by Serpulina (Treponema) hyodysenteriae: inhibition induced by zinc and copper

Serpulina hyodysenteriae produces an oxygen-stable heat-labile hemolysin that may be an important virulence factor in the pathogenesis of swine dysentery. We examine the effect of Ca 2+, Co 2+, Cu 2+, Fe 2+, Mg 2+, Mn 2+, Ni 2+, and Zn 2+ on the hemolytic activity of cell-free supernatant (CFS) from S. hyodysenteriae, isolate B204. Cells harvested from late logarithmic phase cultures were incubated in phosphate-buffered saline containing glucose and RNA-core (PBS-GR) with or without cations and the hemolytic activity of CFS obtained after successive 30 min incubation and washing cycles was determined. The addition of either ZnSO 4 or CuSO 4 to the PBS-GR caused complete inhibition of hemolytic activity after 3 cycles; other cations gave results similar to control extracts. Reduction in the concentration of Zn 2+ in CFS by 60 to 80% after each incubation cycle and binding of Zn 2+ by EDTA indicated that Zn 2+ was associated with the cell fraction, and inhibition of hemolysin activity was specifically mediated by Zn 2+. When the spirochetes were washed after incubation in the presence of ZnSO 4 for 2 cycles and incubated in fresh PBS-GR without Zn 2+, inhibition of hemolysin activity remained unchanged, indicating that the inhibitory effect of ZnSO 4 was due to a direct action of ZnSO 4 on the spirochetes. Since neither the viability of the spirochetes nor the activity of pre-formed hemolysin were affected by the presence of ZnSO 4, the inhibitory effect of Zn 2+ cations was attributed to reduced biosynthesis by viable S. hyodysenteriae cells rather than interference of Zn 2+ cations with lysis of erythrocytes by the hemolysin. Transmission electron microscopic examination of spirochetes after incubation in PBS-GR containing ZnSO 4 revealed clumping of ribosomes and clearing of cell cytoplasm.

In vivo and in vitro toxicity of phospholipase C from Pseudomonas aeruginosa

Pseudomonas aeruginosa produces phospholipase C (PLC), a heat-labile hemolysin. Histopathological analysis of PLC-treated mice revealed that the primary target organs involved in PLC-induced toxicity were the liver and kidney. Mice treated i.v. with PLC demonstrated significant tubular epithelial necrosis of the kidney with hematuria, while when given i.p. they exhibited hepatonecrosis with cellular infiltration. Splenomegaly was also a consistent finding. Results from in vitro studies indicate that PLC is toxic for mouse peritoneal cells and human leukocytes.

Nucleotide sequence and expression of an extracellular hemolysin gene of Aeromonas hydrophila

The extracellular hemolysin (AHH1) gene of Aeromonas hydrophila ATCC7966 was cloned into Charomid928 in Escherichia coli DH1, and its complete nucleotide sequence determined. Escherichia coli carrying this gene expressed an extracellular heat-labile hemolysin for rabbit red blood cells. The minimum size of the coding region of the 2.6 kilobase-pair BamHI- SphI fragment was subcloned into pUC118 and pUC119, selecting for hemolytic activity. The nucleotide sequence of this region contained a single open reading frame of 1734 base pairs, corresponding to a protein of 577 amino acid residues (63658 daltons). A consensus promoter sequence was present upstream of the AHH1 open reading frame. Maxicell analysis of [ 35S] methionine-labelled proteins in E. coli CSR603 carrying the AHH1 plasmid suggested that AHH1 gene codes for an approximately 60000 dalton polypeptide. By colony DNA-DNA hybridization analysis, the AHH1 gene was detected in 43 of 62 hemolysin-producing strains of A. hydrophila (isolated from various sources and areas) and in all 43 hemolysin-producing strains of A. salmonicida (isolated from fish). Three hemolysin-negative strains of A. hydrophila did not react with the AHH1 probe, whereas three non-hemolytic A. salmonicida strains hybridized with the probe.

Purification of phospholipase-C from Bacillus cereus by affinity chromatography on 2-(4-aminophenylsulphonyl)ethyl-cellulose

A new method for the purification of phospholipase-C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) from Bacillus cereus has been developed, based on its affinity to 2-(4-aminophenylsulphonyl)ethyl derivative of beaded cellulose. The enzyme was adsorbed on the affinity sorbent through a site(s) that was clearly distinct from its catalytically active site, because it was still active in the immobilized state. A possible role of enzyme-inhibitor interaction in enzyme binding to the ligand used is discussed.

Do thylakoids really contain phosphatidylcholine?

Isolated intact spinach chloroplasts were incubated with phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) under mild experimental conditions in which only the phosphatidylcholine localized in the cytosolic leaflet of the outer envelope membrane can be hydrolyzed. Thylakoids, which were protected from phospholipase C degradation, were subsequently prepared from the phospholipase C-treated chloroplasts and found to be devoid of phosphatidylcholine. Previously reported occurrences of phosphatidylcholine in thylakoid preparations probably reflect contamination of the thylakoids by envelope membranes. In the present work, contamination of thylakoids by envelope membranes was determined by measuring the 1,2-diacylglycerol 3-beta-galactosyltransferase [monogalactosyldiacylglycerol (MGDG) synthase; UDPgalactose: 1,2-diacylglycerol 3-beta-D-galactosyltransferase, EC 2.4.1.46] in the different chloroplast subfractions. We conclude that phosphatidylcholine is not present in highly purified thylakoids. Phosphatidylcholine is also absent from prokaryotic cyanobacterial membranes, and our results are in agreement with the endosymbiotic origin of higher plant chloroplasts.

Growth hormone activates phospholipase C in proximal tubular basolateral membranes from canine kidney.

To delineate pathways for "signal" transduction by growth hormone (GH) in proximal tubule, we incubated basolateral membranes isolated from canine kidney with human growth hormone (hGH) or human prolactin (hPrl) and measured levels of inositol trisphosphate (InsP3) in suspensions and of diacylglycerol extractable from the membranes. Incubation with hGH, but not hPrl, increased levels of InsP3 and diacylglycerol in a concentration-dependent manner. Half-maximal effects occurred between 0.1 and 1 nM hGH. Increased levels of InsP3 were measured after as little as 5 sec of incubation with 1 nM hGH, and increase was maximal after 15 sec. Increases were no longer detectable after 60 sec because of dephosphorylation of InsP3 in membrane suspensions. hGH did not affect rates of dephosphorylation. hGH-stimulated increases in InsP3 were detectable in membranes suspended in 0, 0.1, and 0.2 mM calcium but not in 0.3 or 1.0 microMs calcium. 125I-labeled hGH-receptor complexes with Mr values of 66,000 and 140,000 were identified in isolated basolateral membranes. Our findings establish that GH activates phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) in isolated canine renal proximal tubular basolateral membranes, potentially after binding to a specific receptor. This process could mediate "signal" transmission by GH across the plasma membrane of the proximal tubular cell and elsewhere.

Induction of inflammatory mediators (histamine and leukotrienes) from rat peritoneal mast cells and human granulocytes by Pseudomonas aeruginosa strains from burn patients

Clinical isolates of Pseudomonas aeruginosa from severely burned patients were analyzed with regard to their capacity to induce inflammatory-mediator release from rat mast cells or human granulocytes. The bacterial strains were characterized according to their cell-associated hemolysin activity as well as their secreted hemolysin and phospholipase C activities. P. aeruginosa expressing heat-labile hemolysin and phospholipase C induced histamine release from rat mast cells and leukotriene formation from human granulocytes, while bacterial strains expressing heat-stable hemolysin were potent releasers of histamine but did not lead to leukotriene formation. The mediator-inducing capacity was dependent on the growth characteristics of the bacterial strains. The purified glycolipid (heat-stable hemolysin) of P. aeruginosa was a potent inducer of histamine release but did not initiate leukotriene formation. Exotoxin A did not affect inflammatory-mediator release. P. aeruginosa with leukotriene-inducing capacity also enhanced omega oxidation of endogenous leukotriene B4, suggesting an additional inactivation of the chemotactic potential. Our data suggest that both hemolysins of P. aeruginosa contribute to the pathogenicity of P. aeruginosa by inducing and modulating inflammatory-mediator release from various cells.

Serotype-related differences in production and type of heat-labile hemolysin and heat-labile cytotoxin of Actinobacillus (Haemophilus) pleuropneumoniae

Reference strains of serotypes 1 to 12 of Actinobacillus (Haemophilus) pleuropneumoniae were cultured in Eagle minimal essential medium with 10% Serum Plus. Culture supernatants were examined for cytotoxicity to alveolar macrophages and for the ability to hemolyze sheep erythrocytes. All strains except the reference strain of serotype 6 produced cytotoxin, whereas only serotypes 1, 5, 9, 10, and 11 produced hemolysin. Both cytotoxin and hemolysin appeared to be heat labile. Antisera were raised against cytotoxin- and hemolysin-containing culture supernatants of serotypes 1 to 11. Cross-neutralization studies revealed that the hemolysins were serologically homogeneous. In contrast, four serologically different cytotoxins were distinguished. One cytotoxin was produced by serotypes 1, 5, 9, and 11, and a second was produced by serotypes 2, 3, 4, and 8. A third cytotoxin was produced by serotypes 7 and 12; this cytotoxin was related to the cytotoxins of serotypes 1, 2, 4, 5, 9, and 11. A fourth cytotoxin, produced by serotype 10, was related to the cytotoxin of serotypes 1, 5, 9, and 11. Seventy field strains belonging to serotypes 2, 3, 7, 8, 9, and 11 were also tested for production of cytotoxin and hemolysin. All strains belonging to serotypes 9 and 11 produced hemolysin and cytotoxin, whereas all strains of serotypes 2, 3, 7, and 8 produced only cytotoxin. Hemolysins and cytotoxins of both the field strains and the corresponding serotype reference strains were comparably neutralized. These findings strongly suggest that the observed differences in production and type of hemolysin and cytotoxin were related to serotype and not to strain.

Membrane phospholipid polar heads influence the coupling of M2 muscarinic receptors to G proteins

Treating membranes from rat heart with phospholipase C (phosphatidylcholine choline phosphohydrolase) from Clostridium perfringens increased the affinity of muscarinic acetylcholine receptors (M2) for the agonists carbachol and oxotremorine. The affinity for antagonists was not affected. Phospholipase C activity, i.e., the cleavage of polar heads of membrane phospholipids, led to the disappearance of the guanine nucleotide-dependent rightward shift of the isotherm for agonist binding. The treatment of tracheal smooth muscle with phospholipase C led to a decrease in the maximum contractile effect of muscarinic (M2) stimulation with no modification of the agonist EC50, i.e., to the uncoupling of the stimulation-contraction process. These results demonstrate that when phospholipid polar heads are hydrolysed by phospholipase C, M2 receptors are uncoupled from G proteins, which enhances their affinity for agonists but prevents information transfer.

Receptor-mediated release of endothelium-derived relaxing factor and prostacyclin from bovine aortic endothelial cells is coupled.

Bovine aortic endothelial cells were grown on microcarrier beads and were perfused with Krebs-Ringer solution. Endothelium-derived relaxing factor (EDRF) was bioassayed on a cascade of four strips of rabbit aorta, and prostacyclin was analyzed by RIA of 6-oxo-prostaglandin F1 alpha. The endothelial cells released EDRF and prostacyclin when stimulated with bradykinin and its analogues, or with ADP, ATP, arachidonic acid, and phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3). The detection of EDRF was potentiated by superoxide dismutase, and the relaxation of rabbit aortic strips induced by EDRF was antagonized by methylene blue. The release of EDRF and prostacyclin was inhibited by phorbol myristate acetate, R59022 (a diacylglycerol kinase inhibitor), and gentamycin. We suggest that the release of EDRF and prostacyclin is coupled and the initial common step is activation of a phospholipase C.

Nucleotide sequences and expression in Escherichia coli of the in-phase overlapping Pseudomonas aeruginosa plcR genes.

The translation products of chromosomal DNAs of Pseudomonas aeruginosa encoding phospholipase C (heat-labile hemolysin) have been examined in T7 promoter plasmid vectors and expressed in Escherichia coli cells. A plasmid carrying a 4.7-kilobase (kb) DNA fragment was found to encode the 80-kilodalton (kDa) phospholipase C as well as two more proteins with an apparent molecular mass of 26 and 19 kDa. Expression directed by this DNA fragment with various deletions suggested that the coding region for the two smaller proteins was contained in a 1-kb DNA region. Moreover, the size of both proteins was reduced by the same amount by an internal BglII-BglII DNA deletion, suggesting that they were translated from overlapping genes. Similar results were obtained with another independently cloned 6.1-kb Pseudomonas DNA, which in addition coded for a 31-kDa protein of opposite orientation. The nucleotide sequence of the 1-kb region above revealed an open reading frame with a signal sequence typical of secretory proteins and a potential in-phase internal translation initiation site. Pulse-chase and localization studies in E. coli showed that the 26-kDa protein was a precursor of a secreted periplasmic 23-kDa protein (PlcR1) while the 19-kDa protein (PlcR2) was mostly cytoplasmic. These results indicate the expression of Pseudomonas in-phase overlapping genes in E. coli.

Studies on [formula omitted][formula omitted] (echinodermata) coelomocyte lysate I. Hemolytic activity of coelomocyte hemolysins

The Holothuriapolii coelomocyte lysate contains two trypsin-resistant lytic proteins having different chemico-physical properties : a calcium dependent and heat-labile hemolysin that is probably a constitutive component of the coelomic fluid, and another calcium independent and heat-stable one that is released after immunological stimulation; it is therefore not detectable in natural conditions. The sphingomyelin seems to be the membrane receptor with which both hemolysins interact producing lysis.

Nucleotide sequence and expression of a phosphate-regulated gene encoding a secreted hemolysin of Pseudomonas aeruginosa.

A 3.3-kilobase-pair fragment of Pseudomonas aeruginosa DNA containing the phospholipase C (heat-labile hemolysin) gene was sequenced, and the location of the gene was determined. The gene product contains at its NH2 terminus a 38-amino acid sequence which structurally resembles the signal peptides of other secreted proteins but is unusually long and positively charged (6+). The location of the translation start codon was determined by constructing a series of plasmids in which the promoter of a transcription vector was ligated to Pseudomonas DNA containing deletions at the 5' end of the gene. The plasmids were used to transform Escherichia coli, and the resulting clones were assayed for hemolysin activity. In addition, sizes of truncated proteins produced by mutants with translation terminators introduced at specific sites were analyzed in E. coli maxicells. The gene is transcribed, starting just upstream of the hemolysin gene, as an mRNA of approximately 2,800 bases. Analysis of the nucleotide sequence, analysis of mutants in maxicells, and transcriptional studies indicate that the hemolysin is part of an operon composed of two genes. Phosphate regulation of the operon is at the transcriptional level. The location of the 5' end of the transcript was determined by S1 mapping.

Charged detergents enhance the activity of phospholipase C ( Bacillus cereus) towards micellar short-chain phosphatidylcholine

Phospholipase C (phosphatidylcholine cholinephosphohydrolase, E.C. 3.1.4.3.) Bacillus cereus) activity toward diheptanoylphosphatidylcholine is increased 50–100% by low concentrations of both positively and negatively charged detergents. Zwitterionic and nonionic detergents have no such activating effect. This charged detergent activation requires an interface, since comparable detergent concentrations have no effect on the hydrolysis rate of monomeric dihexanoylphosphatidylcholine. From NMR and diacylglycerol solubility studies it is suggested that activation results from detergent interacting with diacylglycerol to accelerate product release from the enzyme.

Induction of ornithine decarboxylase in guinea-pig lymphocytes and its relation to phospholipid metabolism

Treatment of lymphocytes with exogenous phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3.) derived from Clostridium perfringens at concentrations similar to those which induced ornithine decarboxylase ( L-ornithine carboxy-lyase, EC 4.1.1.17) activity produced diacylglycerol and phosphatidate. A divalent cation ionophore, A23187, and phytohemagglutinin induced not only diacylglycerol formation, but also ornithine decarboxylase activity. Dibutyryl cAMP inhibited both diacylglycerol formation and ornithine decarboxylase induction to a similar extent in phytohemagglutinin-stimulated lymphocytes, but stimulated them somewhat in ionophore A23187-activated lymphocytes. This suggests that the activation of intracellular phospholipase C and the formation of diacylglycerol is involved in ornithine decarboxylase induction in lymphocytes.