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PubMed1987

Selective release of phospholipase A2 and lysophosphatidylserine-specific lysophospholipase from rat platelets.

Rat platelets released phospholipase A2 and lysophospholipase upon activation with thrombin or ADP. The release of phospholipases was energy-dependent and was not in parallel with that of a known lysosomal marker enzyme, N-acetyl-beta-D-glucosaminidase. The phospholipases are derived from other granules (dense granules or alpha-granules) rather than lysosomal granules of the cells. All of the activities of both phospholipases in the cell free fraction obtained from the activated platelet reaction mixture was recovered in the supernatant after centrifugation at 105,000 X g. The degree of hydrolysis of phospholipids by the phospholipase A2 followed the order: phosphatidylethanolamine (PE) greater than phosphatidylserine (PS) greater than phosphatidylcholine (PC). Phospholipase A2 shows a broad pH optimum (greater than pH 7.0) and absolutely requires Ca2+. Lysophospholipase was specific to lysophosphatidylserine (lysoPS), and neither lysophosphatidylethanolamine (lysoPE) nor lysophosphatidylcholine (lysoPC) was hydrolyzed appreciably. Both 1-acyl- and 2-acyl-lysophosphatidylserine were equally hydrolyzed. Lysophospholipase activity shows similar pH optimum to phospholipase A2. The lysophospholipase activity was lost easily at 60 degrees C. The activity was reduced by the presence of EDTA, though low but distinct activity was observed even in the presence of EDTA. Addition of Ca2+ to the mixtures restores the full activity.

Animals↗

PubMed1989

Platelet activation by tetraprenol via stimulation of phospholipase A2 action.

Only tetraprenol (n = 4), among the (n)-polyprenols studied, induced activation of rabbit platelets. Tetraprenol-induced responses, including platelet aggregation, Ca2+ mobilization, inositol phosphate formation, and arachidonic acid release, were greatly inhibited by a thromboxane A2 (TXA2) receptor antagonist and a cyclooxygenase inhibitor, indicating an essential role for endogenously produced TXA2. The TXA2-mimetic agonist U46619 induced platelet aggregation, Ca2+ mobilization and phospholipase C action but did not induce arachidonic acid release. These results suggest that arachidonic acid is not released via phospholipase C but by phospholipase A2, and this is also supported by the finding that phospholipase C action was inhibited by depletion of extracellular Ca2+, while arachidonic acid release was not. Full arachidonic acid release was found to be induced by the synergistic action of U46619 and tetraprenol. Therefore, the initial, most essential response induced by tetraprenol is a small arachidonic acid release by phospholipase A2, which results in initial TXA2 formation. Further action of phospholipase C as well as Ca2+ mobilization and aggregation were induced by the initially formed TXA2 while further activation of phospholipase A2 required the synergistic action of tetraprenol and TXA2.

Animals↗

PubMed1995

Phospholipid degradation in rat calcium ionophore-activated platelets is catalyzed mainly by two discrete secretory phospholipase As.

An "A1 type" phospholipase activity with serine-phospholipid preference was released by rat activated platelets. It was distinct from the secretory type II phospholipase A2 [Horigome, K., Hayakawa, M., Inoue, K., and Nojima, S. (1987) J. Biochem. 101, 625-631] and co-purified with the secretory lysophosphatidylserine-selective lysophospholipase activity [Higashi, S., Kobayashi, T., Kudo, I., and Inoue, K. (1988) J. Biochem. 103, 442-447]. Several lines of evidence indicated that a single protein was responsible for the phospholipase A1 and lysophospholipase activities. Marked accumulation of lysophospholipids was observed in rat calcium ionophore-activated washed platelets and both phospholipase A1/lysophospholipase and type II phospholipase A2 were shown to contribute to this phospholipid degradation. A selective inhibitor of type II phospholipase A2 reduced the phospholipid degradation and enhanced the clotting time and prothrombinase activity. These results indicate that secretory platelet phospholipases may play a role in regulation of blood clotting.

Animals↗

PubMed2004

Experimental Helicobacter felis infection in transgenic mice expressing human group IIA phospholipase A2.

BACKGROUND: Both various virulence factors of Helicobacter pylori and host factors influence the clinical outcome of H. pylori infection. In animal experiments with Helicobacter felis, large variations in the severity of disease have been observed between different mouse strains infected with a single isolate of H. felis. C57BL/6 J mouse strain that lacks the expression of group IIA phospholipase A2 has been shown to develop more severe gastric inflammation than other mouse strains. Thus, group IIA phospholipase A2 has been suggested to play a role in regulating inflammation in gastric mucosa. The aim of this study was to examine the possible role of group IIA phospholipase A2 in experimental Helicobacter infection. MATERIALS AND METHODS: Transgenic mice expressing human group IIA phospholipase A2 and their group IIA phospholipase A2 deficient nontransgenic C57BL/6 J littermates were infected with H. felis. The mice were killed 3, 8, and 19 weeks after inoculation of bacteria to determine the histopathological changes in gastric mucosa. RESULTS: The infected mice developed chronic inflammation in gastric mucosa. We found no differences in the colonization of bacteria between transgenic and nontransgenic mice. At 3 and 8 weeks, no difference was found in the severity of inflammation between the two groups. Nineteen weeks after the administration of bacteria the inflammation was more marked in nontransgenic than transgenic mice. Group IIA phospholipase A2 was expressed by in situ hybridization in the neck cells of the glandular stomach in transgenic mice. CONCLUSIONS: The results of the present study suggest that the endogenous expression of group IIA phospholipase A2 diminishes chronic inflammation in gastric mucosa in experimental H. felis infection in mice.

Animals↗

PubMed1990

Calcium in renal cells. Modulation of calcium-dependent activation of phospholipase A2.

Calcium has been implicated as a regulatory factor in many physiological and pathophysiological processes in the renal cell. Under physiological conditions, the cytosolic free calcium concentration is maintained at approximately 100 nM. Most of the releasable cell Ca2+ resides in the nonmitochondrial compartments. In addition to the plasma membrane Ca2+ transport processes, there is a high-affinity, low-capacity buffering capability of nonmitochondrial organelles and a lower-affinity high-capacity mitochondrial Ca2+ buffering capability. A critical enzymatic effector of Ca2+ action in the cell is phospholipase A2. By using digitonin-permeabilized renal mesangial cells, the [Ca2+] dependency of phospholipase A2 was characterized. The [Ca2+] sensitivity was insufficient to explain the phospholipase A2 activation observed with vasopressin. In both intact cells, as well as permeabilized cells, it was found that protein kinase C activation markedly enhanced the Ca2+ calmodulin-dependent activation of phospholipase A2. In response to platelet-derived growth factor, it was found that arachidonic acid release preceded phospholipase C activation. This suggests that other effectors besides Ca2+ and protein kinase C may also be important for phospholipase A2 activation. In an experimental model designed to mimic postischemic reperfusion damage to renal mitochondria, it was demonstrated that reactive oxygen species act synergistically with Ca2+ to activate mitochondrial phospholipase A2, which mediates damage to site I of the electron transport chain, the F1F0 ATPase, and the adenine nucleotide translocase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2001

Oxidant-induced inhibition of myocardial calcium-independent phospholipase A2.

We discovered the acute inhibition of myocardial phospholipase A2 activity by micromolar concentrations of tert-butyl hydroperoxide and hydrogen peroxide. Specifically, freshly isolated adult rat cardiomyocytes were treated with the oxidants for 30 min, and phospholipase A2 activity was assessed in cell subcellular fractions using (16:0, [3H]18:1) plasmenylcholine and phosphatidylcholine substrates in the absence or presence of calcium. Calcium-independent phospholipase A2 activity was inhibited by approx 50% in both the cytosolic and membrane fractions by the oxidants. The inhibition of the phospholipase A2 activity was concentration dependent and preceded detectable changes in cell viability as assessed by lactate dehydrogenase release and rod-shaped morphology. Taking into account that oxidized sn-2 fatty acyl groups must first be hydrolyzed by phospholipase A2 to be repaired by glutathione peroxidase, we suggest that the observed inhibition of phospholipase A2 activity by oxidants compromises the myocyte's ability to deal with lipid peroxidation. This conclusion was further validated by the experiments in which pretreatment with the calcium-independent phospholipase A2 inhibitor bromoenol lactone exacerbated cardiotoxicity of tert-butyl hydroperoxide in myocyte cultures.

Animals↗

PubMed1980

Regeneration of full enzymatic activity by reoxidation of reduced pancreatic phospholipase A2.

Reduction of porcine pancreatic phospholipase A2 with 2-mercaptoethanol in the presence of 6M guanidinium hydrocholoride or 8M urea resulted in the complete disruption of all seven disulfide bridges and the concomitant loss of all enzymatic activity. Through aerobic oxidation of the reduced protein at pH 8.0 in the presence of 5 mM cysteine and 0.9M guanidinium hydrochloride up to 90% of the specific activity of the native enzyme was restored. After purification of the reoxidized phospholipase A2 by Sephadex G-75 gel filtration and chromatography on CM-cellulose pure phospholipase A2 was obtained in 80% yield. This purified reoxidized phospholipase A2 was found to be indistinguishable from the native enzyme as judged by its enzymatic activity, lipid and Ca2+ binding properties. Similar results were obtained using S-sulfonated phospholipase A2, prophospholipase A2 or Nepsilon-amidinated phospholipase A2. For the latter two proteins reoxidation was slower than that of the reduced phospholipase A2.

Animals↗

PubMed1988

Inhibition of phospholipase A2 isoenzymes in human endometrium by mefenamic acid and indomethacin: modulation by calcium ions.

The inhibition of endometrial phospholipase A2 activity by the non-steroidal anti-inflammatory agents mefenamic acid and indomethacin was studied over the concentration range 1 mmol/1-0.1 mumol/l. Both phospholipase A2 type 1 (a calcium-dependent enzyme) and phospholipase A2 type 2 (a calcium-independent enzyme) were inhibited by mefenamic acid, but the magnitude of the inhibition was dependent on calcium concentration. Phospholipase A2 type 1 was inhibited 50% by 10 mumol mefenamic acid/l in the presence of 1.25-5 mmol calcium/l, but a concentration of 2.2 mmol mefenamic acid/l was required for 50% inhibition in the absence of calcium. On the other hand, phospholipase A2 type 2 was inhibited 50% by 22 mumol mefenamic acid/l in the absence of calcium and by 100 mumol mefenamic acid/l in the presence of calcium (2.5 mmol/l). Although indomethacin was a less effective inhibitor of phospholipase A2 activity, a similar relationship with calcium was demonstrated. However, indomethacin also had a stimulatory effect on phospholipase A2 type 1 activity in the absence of calcium. Our findings suggest that the two endometrial enzymes may be inhibited by different mechanisms and that the dependence of the enzyme on calcium for activation may be a contributing factor.

Calcium↗

PubMed1986

Decreased phospholipase A2 activity in plasma and liver in uncontrolled diabetes mellitus. A defect in the early steps of prostaglandin synthesis?

Arachidonic acid metabolites and prostaglandins participate in numerous physiologic functions. An enzyme important in the control of prostaglandin production is phospholipase A2. In this study, we have investigated the changes in plasma and hepatic phospholipase A2 activity in diabetes mellitus. In uncontrolled diabetic patients, the postheparin plasma phospholipase A2 level was 18.7 +/- 4.1 U/ml; this value was significantly different from the enzyme activities in control subjects (106 +/- 9.8 U/ml) and in controlled diabetic patients (87 +/- 7.3 U/ml). In the streptozocin-induced diabetic rat model, the postheparin plasma phospholipase A2 level (1.9 +/- 0.45 U/ml) was also decreased when compared with normal (9.4 +/- 1.6 U/ml) and controlled diabetic rats (7.0 +/- 1.3 U/ml). The total hepatic enzyme activity in the uncontrolled diabetic rats was only 21.6% of that seen in control rats. Subcellular fraction studies demonstrated that the enzyme activity is decreased in all fractions in the liver. Liver perfusion studies showed that the heparin-releasable phospholipase A2 activity in the perfusate was significantly decreased in the diabetic rats when compared with control and controlled diabetic animals. We conclude that postheparin plasma and hepatic phospholipase A2 activities are decreased in uncontrolled diabetes mellitus, that the low plasma activity is related to decreased release from the liver, and that the alterations in phospholipase A2 activity in plasma and liver are restored to normal by controlling the diabetic status.

Adult↗

PubMed1990

Determination of human serum phospholipase A2. Comparison of two methods.

A photometric assay for serum phospholipase A is compared with a radiometric assay specific for phospholipase A2. The methods show a high correlation. The increased phospholipase A activity in sera of patients with inflammatory and non-pancreatic necrotizing diseases is attributable to a neutral-active, calcium-sensitive phospholipase A2 but not to pancreatic phospholipase A2. Phospholipase A1 did not seem to contribute significantly to the overall activity of phospholipase A.

Evaluation Studies as Topic↗

PubMed1988

The chemical basis for interfacial activation of monomeric phospholipases A2. Autocatalytic derivatization of the enzyme by acyl transfer from substrate.

A basic monomeric phospholipase A2 from the venom of the American water moccasin, Agkistrodon piscivorus piscivorus, undergoes Ca2+-dependent, autocatalytic acylation during the course of hydrolysis of both model and natural phospholipid substrates. Acylation occurs at 2 lysine residues, Lys-7 and Lys-10, in the NH2-terminal alpha-helical segment of the enzyme, and when both positions are fully derivatized, the stable bisacylphospholipase A2 becomes a dimer in solution. The acylated enzyme is fully activated toward monomolecular layers of lecithins. Similar studies applied to the monomeric phospholipases A2 from porcine pancreas and from the venom of Agkistrodon contortrix contortrix also showed irreversible activation of the enzymes by substrate with the same kinetic consequences and formation of dimers. Acylation thus enables these enzymes to overcome the lag period observed under such conditions with native monomeric phospholipases, a phenomenon referred to as interfacial activation. Activation of the enzyme by acylation potentiates the phospholipase for interfacial recognition via formation of a dimeric enzyme. The naturally occurring phospholipase A2 dimer from Crotalus atrox venom displays no lag in the hydrolysis of lecithin monolayers nor does it undergo substrate level acylation. These facts support our proposal that dimerization concomitant with acylation is responsible for the large rate enhancements seen in the hydrolysis of aggregated phospholipids by monomeric phospholipases. Our findings demonstrate for the first time a chemical mechanism for interfacial activation of and interfacial recognition by phospholipases A2.

Amino Acid Sequence↗

PubMed1987

Identification and isolation of a mammalian protein which is antigenically and functionally related to the phospholipase A2 stimulatory peptide melittin.

Antibodies prepared against the phospholipase A2 stimulatory peptide melittin were used to identify and isolate a novel mammalian protein with similar functional and antigenic properties. The mammalian protein of Mr 28,000 was isolated from cell sonicates by high performance immunoaffinity chromatography and size exclusion chromatography. This stimulatory protein was stable for several months when frozen at -70 degrees C. The purified protein selectively stimulated phospholipase A2 when phosphatidylcholine was used as a substrate but had no effect on phospholipase A2 activity when phosphatidylethanolamine was used as a substrate. Furthermore, this protein had no effect on phospholipase C activity or on pancreatic or snake venom phospholipase A2. The stimulatory activity was unaffected by RNase or DNase treatment. However, boiling or trypsin digestion inactivated the phospholipase stimulatory activity. The mechanism of phospholipase A2 stimulation appeared to result from an increase in the apparent Vmax of the enzyme.

Animals↗

PubMed1979

Separation and purification of a potent bactericidal/permeability-increasing protein and a closely associated phospholipase A2 from rabbit polymorphonuclear leukocytes. Observations on their relationship.

Two antibacterial proteins from rabbit polymorphonuclear leukocytes, a potent bactericidal cationic protein that increases the envelope permeability of susceptible gram-negative bacteria and a phospholipase A2, have been purified to near homogeneity by ion exchange, gel filtration, and hydrophobic interaction chromatography. The apparently noncatalytic bactericidal/permeability-increasing protein has an approximate molecular weight of 50,000 and is isoelectric at pH 9.5 to 10.0. The molecular properties, including amino acid composition, and the antibacterial potency and specificity of this rabbit leukocyte protein and of the bactericidal/permeability-increasing protein from human granulocytes that we have recently purified (J. Biol. Chem. 253, 2664-2672, 1978) are closely similar. Both proteins kill several strains of Escherichia coli and Salmonella typhimurium. Rough strains are more sensitive than smooth strains. All gram-positive bacterial species tested are insensitive to high concentrations of either rabbit or human protein. The phospholipase A2, purified by hydrophobic interaction chromatography on phenyl-Sepharose, ran as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular weight of 14,000 and had a specific enzymatic activity comparable to that of purified phospholipases A2 from other sources. Separation of the phospholipase A2 from the bactericidal/permeability-increasing protein has no noticeable effect on the bactericidal and permeability-increasing activities of the purified bactericidal protein, but removes the ability of the phospholipase A2 to hydrolyze the phospholipids of intact Escherichia coli. Upon recombination of the phospholipase A2 with the bactericidal/permeability-increasing protein, the phospholipase A2 regains its activity toward the phospholipids of intact E. coli suggesting that these two antibacterial leukocyte proteins act in concert.

Amino Acids↗

PubMed1984

A new class of phospholipases A2 with lysine in place of aspartate 49. Functional consequences for calcium and substrate binding.

We report here the discovery of a new class of phospholipases A2 in which Asp-49, a residue considered to be an obligate component of the catalytic apparatus, is replaced by a lysine. Asp-49 is invariant among the more than 30 venom and pancreatic phospholipases A2 sequenced to date, and its beta-carboxylate group has been shown to be a ligand for calcium in a binding site which also involves contributions from the peptide carbonyl oxygens of Tyr-28, Gly-30, and Gly-32, the so-called calcium-binding loop. The change of Asp-49 to a lysine, and other substitutions in regions heretofore thought to be invariant, including the calcium-binding loop, suggested that the new phospholipases might differ functionally with respect to calcium and/or substrate binding. Indeed, although the Lys-49 phospholipases A2 show a dependence on calcium similar to that of the Asp-49 enzymes, they may be distinguished by the fact that, in the absence of phospholipid, they do not bind calcium to any measurable extent under conditions where Asp-49 enzymes bind a stoichiometric amount of calcium. Furthermore, in the absence of calcium, they show binding to single bilayer phospholipid vesicles under conditions where Asp-49 phospholipases do not bind at all. These results suggest a reversed order of addition of calcium and substrate in the formation of the ternary catalytic complex in the Lys-49 phospholipases A2. Although the mechanistic implications of these structural and functional alterations are not defined at present, it is clear that Asp-49 is not essential for phospholipase A2 catalysis and that it does not participate in the enzyme-calcium-phospholipid catalytic complex.

Amino Acid Sequence↗

PubMed1981

[Interaction of cytotoxin and Ca2+ with phospholipase A2].

The effects of Ca2+ and cytotoxin from Middle Asian cobra venom on the hydrolytic activity of phospholipase A2 from the same source and on its action on erythrocyte membrane phospholipids and mitochondria were studied. The necessity of phospholipase A2 for Ca2+ depends on the type of substrates (phosphatidyl methanol, phosphatidyl ethanol, cephalin, phosphatidyl ethyleneglycol, phosphatidyl inositol), whereas enzymatic cleavage of lecithin can also occur in the absence of Ca2+. Cytotoxin Vc" I had no effect on the rate of phospholipid hydrolysis in the absence of Ca2+. However, in the presence of Ca2+ cytotoxin at low concentrations activated phospholipase A2, while its high concentrations inhibited the phospholipid hydrolysis with the exception of phosphatidyl ethyleneglycol and phosphatidyl inositol. In experiments with purified phospholipids no synergistic effect of cytotoxin and phospholipase A2 was observed. The activating effect of cytotoxin and phospholipase A2 was comparable to that of the cationic detergents. The effect of phospholipase A2 on erythrocyte hemolysis and succinate oxidation by mitochondria was more complicated: the activating or inhibiting effect depended on the state and ratio of Ca2+, cytotoxin and phospholipase A2. It is suggested that the synergistic effect observed in membrane systems is primarily due to the structural organization of the membranes and the phase condition of the membrane phospholipids.

Animals↗

PubMed1981

[Effect of phospholipase A2 from the venoms of bee and Middle Asian cobra on choline uptake by synaptosomes].

The effect of purified phospholipase A2 from venom of the bee Apis mellifica and from venom of the cobra Naja naja oxiana on the Na+-dependent high affinity choline transport into the synaptosomes of rabbit corpus striatum (active uptake) was studied. Both phospholipases A2 were shown to inhibit the active choline uptake by the synaptosomes. The bee venom phospholipase at a concentration of 10(-8) M and the cobra venom phospholipase at a concentration of 10(-6) M produced a 50% inhibition of choline uptake. A relationship was found between the enzymatic activity of the phospholipases and their ability to block choline uptake by the synaptosomes. A removal of Ca-ions from the medium abolished the effects of both phospholipases. Replacement of Ca2+ by Sr2+ inhibited the effect of the cobra venom phospholipases but did not inhibit that of bee venom enzyme.

Animals↗

PubMed1990

Choline deficiency activates phospholipases A2 and C in rat liver without affecting the activity of protein kinase C.

There is evidence to suggest that liver tumor promoters exert their effect through the interference of signal transduction in hepatic cells. Both phospholipase A(2) and phospholipase C play important roles in the generation of second messengers and in the activation of Ca(2+), phospholipid-dependent protein kinase C. Using male Sprague-Dawley rats, we investigated whether liver tumor-promoting regimens of a choline-deficient diet and phenobarbital alter the activities of phospholipase A(2) and phospholipase C in the liver, and extended the study to determine the effect of a choline-deficient diet on protein kinase C activities. Feeding a choline-deficient diet for 1 week increased the activities of both phospholipase A(2) (50%) and phospholipase C (22%), and the activities of both enzymes were more than doubled after 4 weeks. Feeding a phenobarbital diet resulted in a slight decrease in phospholipase A(2) activities at 4 weeks but no significant changes in PLC activities. The protein kinase C activities and its distribution between soluble and particulate fractions remained unchanged after 1, 2, and 4 weeks feeding of a choline-deficient diet. Thus, activation of both phospholipase A(2) and C is distinct for a choline-deficient diet, not shared by phenobarbital diet. Increased activities of these enzymes were not associated with the activation of protein kinase C under the present experimental condition.

Journal Article↗

PubMed2001

Phosphoinositide-specific phospholipase Cbeta1 expression is not linked to nerve growth factor-induced differentiation, cell survival or cell cycle control in PC12 rat pheocromocytoma cells.

Recent reports have highlighted that phosphoinositide-specific phospholipase Cbeta1 expression is linked to neuronal differentiation in different experimental models. We sought to determine whether or not this is also true for nerve growth factor (NGF)-induced neuronal differentiation of rat PC12 cells. However, we did not find differences in the expression of both the forms of phosphoinositide-specific phospholipase Cbeta1 (a and b) during sympathetic differentiation of these cells. Also, PC12 cell clones stably overexpressing phosphoinositide-specific phospholipase Cbeta1 were not more susceptible to the differentiating effect of NGF. Furthermore, since it is well established that phosphoinositide-specific phospholipase Cbeta1 affects cell proliferation, we investigated whether or not PC12 cell clones stably overexpressing phosphoinositide-specific phospholipase Cbeta1 showed differences in survival to serum deprivation and cell cycle, when compared to wild type cells. Nevertheless, we did not find any differences in these parameters between wild type cells and the overexpressing clones. Interestingly, in PC12 cells the overexpressed phosphoinositide-specific phospholipase Cbeta1 did not localize to the nucleus, but by immunofluorescence analysis, was detected in the cytoplasm. Therefore, our findings may represent another important clue to the fact that only when it is located within the nucleus phosphoinositide-specific phospholipase Cbeta1 is able to influence cell proliferation.

Animals↗