Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PHOSPHOLIPASE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75Linked to original sources
PubMed1987

The effects of ischaemia, lysophosphatidylcholine and palmitoylcarnitine on rat heart phospholipase A2 activity.

Phospholipase A2 activity was studied in the isolated rat heart following coronary artery ligation. In both the homogenate and mitochondrial fractions phospholipase A2 activity was significantly depressed at 20 min post ligation in the ischaemic region only. This is at a time of peak lysophospholipid concentration and severity of arrhythmias. No such depression of activity was seen in a crude sarcolemmal fraction, possibly due to washout of inhibitory factors during isolation. Lysophosphatidylcholine and palmitoylcarnitine, two amphiphiles known to accumulate during ischaemia, were both shown to be capable of inhibiting phospholipase A2. It is suggested that lysophospholipid and palmitoylcarnitine accumulation during ischaemia may contribute to the depression of phospholipase A2 activity seen and that the decreased metabolism of lysophospholipids may be of more importance in their accumulation than increased production by phospholipase A2.

Animals↗
PubMed1985

Methyltransferase and phospholipase A2 activity in membranes of neutrophils and lymphocytes from patients with bacterial and viral infections.

Phospholipid methylation and phospholipase A2 activation in the cell membrane are necessary for the induction of cell function in neutrophils and lymphocytes. We assessed the activity of membrane-associated methyltransferase and phospholipase A2 in neutrophils and lymphocytes from patients with acute and severe bacterial and viral infections. In bacterial patients, methyltransferase and phospholipase A2 activities of neutrophils were significantly enhanced, and [3H]methyl incorporation of lymphocytes was slightly increased. In viral infections, only phospholipase A2 activity of the lymphocytes was increased. These enhanced enzyme activities paralleled disease activity of the two disorders. The methylated products detected by two-dimensional thin-layer chromatogram were confined to methylated phospholipids, indicating that our assay system measures specifically the activity of methyltransferase which mediates the translocation of membrane phosphatidylethanolamine (PE) to phosphatidylcholine (PC) and lyso-PC(LPC). The two enzymatic activities of both neutrophils and lymphocytes in bacterial infections and phospholipase A2 of lymphocytes may, in part, have some correlation to the defense mechanism in these two disorders.

Adult↗
PubMed1989

Acid phospholipase A1 in liver--a brief survey.

Acid phospholipase A1 activity in liver (rat, human) is predominantly localized in lysosomes. A minor proportion (less than 3% of the total activity) is also present in the Golgi apparatus and the endoplasmic reticulum, presumably due to enzymatically active precursors of the corresponding lysosomal enzyme. Lysosomal phospholipase A1 is the most important enzyme initiating the intralysosomal catabolism of diacylphosphoglycerides. It has been purified 50,600-fold, with a yield of about 26%. The enzyme prefers phosphatidyl-ethanolamine as a substrate, which at 200 microM and pH 4.5, is hydrolysed at a rate of approximately 8.2 U/mg. Lysosomal phospholipase A1 is a glycoprotein of about 29 kDa with an isoelectric point of pH 5.3. Unspecific extralysosomal endogenous inhibitors of this enzyme are pH range, inorganic cations, and various proteins. Divalent cations are more potent inhibitors than monovalent ones. Most endogenous intra- and extracellular proteins inhibit the enzyme, the cationic species exhibiting high inhibitory potencies, glycoproteins only little. Inhibitory proteins act through their binding to the substrate. Lysosomal phospholipase A1 seems to be an important target in drug-induced lipidosis. This lipid storage disease is caused by various cationic amphiphilic drugs that are trapped intralysosomally by protonation. In lysosomes such compounds raise the pH, interact with the polar lipids to be degraded and the lysosomal lipolytic enzymes, such as phospholipase A1. These mechanisms result in impaired intralysosomal phospholipid degradation and hence in intralysosomal phospholipid accumulation.

Humans↗
PubMed1982

Use of phospholipase A to compare phospholipid organization in synaptic membranes, myelin, and liposomes.

The pattern of fatty acid release from rat synaptic membranes in the presence of phospholipase A2 (Vipera russelli) was compared to that from liposomes comprised of phospholipids. Phospholipase A2 more readily attacked myelin and synaptic membranes than liposomes prepared from total phospholipids derived from myelin. Although hydrolysis of liposomal phospholipids occurred in the absence of added calcium, the presence of 2 mM CaCl2 or 2% bovine serum albumin significantly enhanced the phospholipase attack of liposomes, but not synaptic membranes of myelin. Phospholipase exhibited a marked preference for phospholipids containing docosahexaenoic acid (22:6) in the synaptic membranes, while with liposomes the pattern of released fatty acid reflected the fatty acid composition in the two-position of the phospholipids. Although either calcium or albumin markedly increased the phospholipase hydrolysis of liposomes, neither affected the hydrolysis of synaptic membranes or the pattern of fatty acid release from liposomes. It was concluded that the nonlipid constituents, particularly the proteins, of biomembranes were responsible for the organization of the phospholipids and accounted for the observed differences between liposomes and synaptic membranes with respect to enzymic accessibility.

Animals↗
PubMed1987

The degradation of platelet-activating factor and related lipids: susceptibility to phospholipases C and D.

1-O-Octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) is an ether-linked lipid that exhibits selective cytotoxicity toward several types of tumor cells and is relatively inactive toward normal cells under the same conditions of treatment. The mechanis of this selective cytotoxicity is unknown. We conducted studies to determine whether this compound is metabolized by phospholipases C and D and, if so, whether sensitive and resistant cells differ in their ability to degrade ET-18-OCH3 by these enzymes. We have examined the metabolism of the L-isomer of ET-18-OCH3, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (L-ET-18-OCH3), by lysophospholipase D of rat liver microsomes and by a phospholipase D from the marine bacterium Vibrio damsela. The metabolism of L-ET-18-OCH3 was also examined in cell culture using Madin-Darby canine kidney cells, human promyelocytic leukemia cells and human myelocytic leukemia cells. In these studies, L-ET-18-OCH3 and related 1-O-alkyl-linked phosphocholine analogs radiolabeled with 3H in the 1-O-alkyl chain were used. L-ET-18-OCH3 was not hydrolyzed by lysophospholipase D from rat liver microsomes under conditions where cleavage of 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine was observed. However, phospholipase D from the marine bacterium V. damsela readily hydrolyzed L-ET-18-OCH3 to 1-O-[3H]octadecyl-2-O-methyl-sn-glycero-3-phosphate, demonstrating that L-ET-18-OCH3 can be degraded by a phospholipase D. Platelet-activating factor (PAF) and lyso-PAF were also substrates for the bacterial phospholipase D.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Phospholipase A2 assay using an intramolecularly quenched pyrene-labeled phospholipid analog as a substrate.

A phospholipid analog 1-palmitoyl-2-6(pyren-1-yl)hexanoyl-sn-glycero-3-phospho-N- (trinitrophenyl)aminoethanol (PPHTE) in which pyrene fluorescence is intramolecularly quenched by the trinitrophenyl group was used as a substrate for pancreatic phospholipase A2. Upon phospholipase A2 catalyzed hydrolysis of this molecule pyrene monomer fluorescence emission intensity increased as a result of the transfer of the pyrene fatty acid to the aqueous phase. Optimal conditions for phospholipase A2 hydrolysis of PPHTE were similar to those observed earlier for other pyrenephospholipids (T. Thuren, J. A. Virtanen, R. Verger, and P. K. J. Kinnunen (1987) Biochim. Biophys. Acta 917, 411-417). Although differential scanning calorimetry revealed no thermal phase transitions for PPHTE between +5 and +60 degrees C the Arrhenius plot of the enzymatic hydrolysis of the lipid showed a discontinuity at 30 degrees C. The molecular origin of this discontinuity remains at present unknown. To study the effects of dimyristoylphosphatidylcholine (DMPC) phase transition at 23.9 degrees C on phospholipase A2 reaction PPHTE was mixed with DMPC in a molar ratio of 1:200 in small unilamellar vesicles. The hydrolysis of DMPC-PPHTE vesicles was measured by following the increase in pyrene monomer fluorescence emission due to phospholipase A2 action on PPHTE. Below the phase transition of DMPC the enzymatic reaction exhibited a hyperbolic behavior. At the transition as well as at slightly higher temperatures a lag period was observed. The longest lag period was approximately 20 min. Above 26 degrees C no lag time could be observed. However, the reaction rates were slower than below the phase transition temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1982

Aminoglycoside antibiotics inhibit lysosomal phospholipase A and C from rat liver in vitro.

Accumulation of aminoglycoside antibiotics and phospholipids in lysosomes is a prominent feature of aminoglycoside nephrotoxicity, suggesting the possibility that these agents may inhibit the activity of lysosomal phospholipases. We examined the effect of four aminoglycoside antibiotics, amikacin, dibekacin gentamicin and tobramycin, on the hydrolysis of [3H]dioleoylphosphatidylcholine by a lysosomal protein fraction obtained from rat liver which contains phospholipase A and C. Phospholipase A was inhibited strongly by these agents. Phospholipase C was also inhibited, especially by amikacin and tobramycin. These results suggest that the accumulation of phospholipids in the kidney cortex in aminoglycoside nephrotoxicity may be due to inhibition of lysosomal phospholipase action.

Aminoglycosides↗
PubMed1982

Biphasic modulation of platelet phospholipase A2 activity and platelet aggregation by mepacrine (quinacrine).

The modulation of rat platelet phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) and rat platelet aggregation by mepacrine was investigated. The 2-acyl specificity of phospholipase A2 activity was confirmed by using 1-[14C]palmitoyl-2-[3H]arachidonylphosphatidylcholine as substrate. Under optimal pH, phospholipase A2 activity was not affected by aspirin but was inhibited by indomethacin. Contrary to previous reports, a biphasic modulatory role of mepacrine on phospholipase A2 activity and platelet aggregation was demonstrated. The data suggest that platelet aggregation is mediated via phospholipase A2.

Animals↗
PubMed1984

Inhibition of lysosomal phospholipases C and A in rabbit alveolar macrophages, polymorphonuclear leukocytes and rat liver by sodium bisulfite.

Phospholipase C activity was measured in disrupted rat liver lysosomes, Bacillus Calmette Guérin-induced rabbit alveolar macrophages and glycogen-induced rabbit polymorphonuclear leukocytes, using [N-methyl-14C]sphingomyelin and the phospholipids of human myelin. Phospholipase C activity with both substrates was maximal at pH 4.5 and was unaffected by monovalent or divalent cations or EDTA. The enzyme(s) had little or no substrate specificity, since most of the phospholipids of human myelin were degraded to the same extent. Solutions of gentamycin and tobramycin which contained preservatives inhibited activity, whereas similar preparations of streptomycin had no effect. On the other hand, preservative-free solutions of gentamycin and tobramycin were not inhibitory. Sodium bisulfite, an antioxidant, used in commercial preparations of gentamycin, tobramycin, streptomycin and other drugs, produced dose-dependent, reversible inhibition of the sphingomyelinase and myelin-degrading phospholipase C. Moreover, bisulfite-antibiotic interactions protected enzymatic activity from inactivation by the antioxidant. Other preservatives in commercial aminoglycosides, methyl- and propylparaben, phenol and EDTA had no effect on enzymic activity. Sodium bisulfite also inhibited acid-active phospholipase(s) A in rat liver lysosomes and alveolar macrophages, but had no effect on neutral-active, calcium-dependent phospholipases A2 from various cell types. Equimolar concentrations of streptomycin instantaneously relieved most of the inhibition by bisulfite, whereas molar ratios of gentamycin/bisulfite of 10 restored only 50% of the activity.

Animals↗
PubMed1984

pH-dependent modulation of phospholipase A2 activity by alkaline cations and catecholamines in a granule-enriched fraction of adrenal medulla.

Phospholipase A activity was measured in the soluble fractions from bovine adrenal medullary granules and rat liver lysosomes. The adrenal medulla preparation, enriched 2.5-fold in chromaffin granules and lysosomes, hydrolyzes the phospholipids of [1-14C]oleate-labelled autoclaved Escherichia coli in the pH range 3.5-7.0 in an alkaline cation (Na+, K+, Ca2+, Mg2+)-dependent fashion. At low alkaline cation concentrations the apparent pH optimum is near 6.5 but decreases to about 4.5 with increasing cation concentrations. When measured at high alkaline cation concentrations phospholipase activity in the adrenal fraction has a pH profile and optimum similar to those of rat liver lysosomes. Amine-containing buffers, millimolar concentrations of catecholamines and micromolar concentrations of the amine-containing drug, trifluoperazine, modulate the adrenal medulla phospholipase activity in a pH- and alkaline cation-dependent manner. Studies with specifically labelled phosphatidylethanolamines confirm previous conclusions that activity at pH 6.4 is almost exclusively phospholipase A2; but in contrast to previous conclusions (Smith, A.D. and Winkler , H. (1968) Biochem. J. 108, 867-874) we find significant phospholipase A2 activity at pH 4.2.

Adrenal Medulla↗
PubMed1985

Secretion of phospholipase A1 by bone marrow-derived macrophages.

Bone marrow-derived macrophages contain phospholipase activity of the A1 and A2 types, active at acid or neutral pH and with different specificities for the fatty acid to be liberated. In contrast to this variety, only one single phospholipase could be detected in extracellular fluids of these cells. Surprisingly, this phospholipase was of the A1 type and active at about pH 8. It exhibited a restricted substrate specificity in that, of the various substrates tested, only phosphatidylcholine containing palmitic acid in position 2 was degraded. This total restriction was not detected with phosphatidylethanolamine substrates. In addition to phospholipase A1, extracellular fluids exhibited lipase activity. A modulation of enzyme secretion could not be achieved by lymphokines or phorbol esters. However, release could be blocked by treating cells with cycloheximide (5 micrograms/ml) or tunicamycin (0.5 micrograms/ml). Phospholipase A1 was also released by thioglycollate-induced peritoneal macrophages.

Animals↗
PubMed1987

Hydrolysis of 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero- 3-phospholipids by phospholipase A2: effect of the polar head-group.

The effect of the phospholipid polar head-group on the porcine pancreatic phospholipase A2 (phosphatidylcholine 2-acylhydrolase, EC 3.1.1.4) reaction was studied using 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3- phosphatidylcholine, -ethanolamine, -glycerol, -monomethylester and -serine as substrates. Except for the monomethylester analogue, which was maximally activated by 3.5 mM CaCl2, maximal enhancement of hydrolysis of the other pyrenephospholipids was obtained at 2 mM Ca2+. Sodium cholate inhibited hydrolysis of the ethanolamine and serine lipids, whereas a slight (1.4-2.0-fold) activation was observed for the -choline, -glycerol and -monomethylester derivatives. Arrhenius plots of hydrolysis of pyrenephospholipids by porcine pancreatic phospholipase A2 revealed no discontinuities, thus indicating the absence of phase transition for these lipids in the temperature range 15-45 degrees C. Specific activities of porcine and bovine pancreatic, porcine intestinal and snake venom (Crotalus atrox) phospholipases A2 towards pyrenephospholipid liposomes were then compared. Whereas the snake venom phospholipase A2 preferred phosphatidylcholine as a substrate, the other phospholipases A2 preferred acidic phospholipids in the order monomethylester greater than or equal to glycerol greater than or equal to serine.

Animals↗
PubMed1987

Profile of phospholipase A2 activity in subcellular fractions and lamellar bodies of developing, neonatal and adult rabbit lung. Correlation with intracellular levels of disaturated phosphatidylcholine.

Phospholipase A2 activity was determined in subcellular fractions and lamellar bodies of fetal, neonatal and adult rabbit lungs. Specific activity in most fractions decreased from the 24th to the 28th day of gestation. All fractions except the mitochondrial and the nuclear fractions exhibited a sharp increase in activity in the newborn lung. Specific activity in the adult lung generally declined in comparison to neonatal values. During gestation total enzyme activity per gram of lung was concentrated in the cytosolic fraction. With the exception of the lamellar body fraction, the total content of phospholipase A2 activity increased dramatically in all fractions from the neonatal lung. The lamellar body fractions displayed both low specific activity and low total enzyme activity during gestation. Specific activity increased dramatically in the neonatal and adult lung but still accounted for only a small fraction of the activity in comparison to the other subcellular fractions. The subcellular content of disaturated phosphatidylcholine (PC) appeared to correlate well with the activity of phospholipase A2 in the neonatal mitochondrial, microsomal and cytosolic fractions. Since decreasing prenatal enzyme levels are associated with increasing disaturated PC content, the alkaline and calcium-dependent phospholipase A2 may not be directly involved in disaturated PC synthesis in the fetus. However, postnatally, the correlation between the pattern of production of disaturated PC and the activity of the phospholipase A2 indicates a role for this enzyme in surfactant-related disaturated PC synthesis.

Animals↗
PubMed1988

Lipid-induced aggregation of phospholipase A2: sucrose density gradient ultracentrifugation and crosslinking studies.

The aggregation behavior of cobra venom (Naja naja naja) phospholipase A2 in the presence of lipids and Ca2+ was examined using ultracentrifugation and crosslinking techniques. Velocity sedimentation experiments were performed in sucrose gradients. The sedimentation coefficients of the cobra phospholipase A2 and various controls, including bovine serum albumin (BSA), malate dehydrogenase, carbonic anhydrase and pancreatic phospholipase A2, were calculated both in the presence and absence of ligands. The monomeric phospholipid, diheptanoylphosphatidylcholine, and the phospholipid analogue, dodecylphosphocholine (DPC), increased the sedimentation coefficient of the cobra phospholipase A2 from 2.2 S to 2.9 S, a value that is consistent with the formation of an enzyme dimer. The control proteins were unaffected by the presence of phospholipid, except for BSA, which apparently binds large amounts of DPC. Crosslinking experiments with glutaraldehyde showed that in the presence of diheptanoylphosphatidylcholine or DPC, the amount of crosslinked enzyme increased. Ca2+ had no effect on the aggregation state of the enzyme as measured by either technique. Both the ultracentrifugation data and crosslinking data are consistent with the hypothesis that the cobra venom phospholipase A2 exists as a dimer or higher-order aggregate in the presence of lipid substrate, although it is yet to be determined whether the functional subunit is a monomer, dimer or higher-order oligomer.

Barium↗
PubMed1991

Characterization of several phospholipase activities and diacylglycerol/2-monoacylglycerol lipases in rat alveolar macrophages.

We measured phospholipase activities in both the microsomal and the cytosolic enriched fractions of rat alveolar macrophages by using exogenous arachidonic acid-labeled phospholipids. The microsomal fractions contain a neutral calcium-independent phospholipase A2 (PLA2) which acts on substrates phosphatidylcholine (PC) and phosphatidylinositol (PI), a calcium-independent PLA2 acting on phosphatidylethanolamine (PE), and a neutral calcium-dependent PI-specific PLC. The cytosolic fractions contain calcium-dependent phospholipase: PLA2 that hydrolyses PC at alkaline pH, and a neutral PI-specific phospholipase C (PLC). The largest release of arachidonic acid from PI occurred with the cytosolic fractions at pH 6 in the presence of calcium. That hydrolysis involved a PLA2, and a PLC followed by the action of a diacyglycerol and 2-monoacylglycerol lipases. The cytosol also contains a calcium-independent PLA2 acting on PE. Our investigation shows that rat alveolar macrophages possess a number of phospholipases, as well as diacylglycerol and 2-monoacylglycerol lipases. The above enzymes could play an essential role in the remodeling of membrane phospholipids in resting cells, and the generation of physiologically active lipids in activated cells.

Animals↗
PubMed1984

Calcium regulation of phospholipase A2 is independent of calmodulin.

There are conflicting data in the literature as to whether or not the Ca2+ activation of phospholipase A2 is mediated by the calcium binding protein calmodulin. In the present study the membrane-bound phospholipase A2 enzymes in rat and human platelets were shown to be absolutely Ca2+ dependent but were not stimulated by the addition of calmodulin. A partially purified phospholipase A2 from rat platelet membrane, which contained little endogenous calmodulin, also was not stimulated by calmodulin addition. Both isolated and membrane-bound phospholipase A2 were inhibited by the non-specific calmodulin antagonist trifluoperazine but the inhibition was not overcome by adding calmodulin. There was thus no evidence from these studies that phospholipase A2 is calmodulin regulated.

Animals↗
PubMed1990

Monoclonal antibodies against human synovial phospholipase A2.

Four monoclonal antibodies (HP-1, HP-2, HP-3 and HP-4) with differing reactivities were raised against human synovial fluid phospholipase A2. None of them bound to exocrine phospholipases A2, such as those from pancreas or snake venom. However, antibodies HP-1 and HP-3 showed cross-reactivity with rabbit and rat platelet secretory phospholipases A2, which share common enzymatic and structural features with the human synovial enzyme. Antibodies HP-1, HP-2 and HP-3 inhibited the activity of human synovial phospholipase A2. The antibodies were used to develop a rapid immunoaffinity column chromatographic procedure for enzyme purification. In some preparations, the recovery of total activity after immunoaffinity column chromatography was more than 100% suggesting the existence of endogenous inhibitory factors of phospholipase A2 in human synovial fluid.

Animals↗
PubMed1983

Mechanism of endotoxin-induced reduction in the number of beta-adrenergic receptors in dog livers: role of phospholipase A.

The role of phospholipase A on the endotoxin-induced reduction in the number of beta-adrenergic receptors in dog liver plasma membranes was investigated. The results show that digestion of control liver plasma membranes with exogenous phospholipase A2 (0.2 unit/200 micrograms protein) decreased the specific binding of (-)-[3H]dihydroalprenolol by 37.3% (P less than 0.01) and reduced the number of receptor sites by 31.7% (P less than 0.05). These decreases in the specific binding and the number of beta-adrenergic receptors were completely reversible by the addition of phosphatidylcholine (0.2 mM). Endotoxin administration (2 hr postendotoxin) decreased the specific binding by 36% (P less than 0.05) and reduced the number of beta-adrenergic receptors by 33% (P less than 0.05), and these decreases were completely reversible by the addition of 0.2 mM phosphatidylcholine. Digestion of control liver membranes with exogenous phospholipase A2 decreased phosphatidylcholine and phosphatidylethanolamine levels by 50.6 and 51.2%, respectively, but increased lysophosphatidylcholine and lysophosphatidylethanolamine levels by 12- and 8.4-fold, respectively. Endotoxin administration decreased phosphatidylcholine and phosphatidylethanolamine contents by 21.4 and 23.8%, respectively, but increased lysophosphatidylcholine and lysophosphatidylethanolamine contents by 2.1- and 1.4-fold, respectively. In addition, endotoxin administration increased endogenous phospholipase A activity by 73.5%. Based on these results, it is suggested that the decreases in the specific binding and the number of beta-adrenergic receptors in dog livers during endotoxic shock are a result of phospholipase A activation.

Animals↗