Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:O95477 (membrane-bound)
 29,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During collagen-induced blood platelet aggregation, arachidonic acid is set free from membrane phospholipids and subsequently converted into 12-hydroxyeicosatetraenoic acid by arachidonate lipoxygenase and into thromboxane A2, 12-hydroxyheptadecatrienoic acid (HETE) and malondialdehyde by cyclooxygenase and thromboxane synthase. Lipoxygenase and cyclooxygenase have optimal activity at neutral to basic pH, while the thromboxane synthase is pH-independent between 5 and 9. These enzymes are membrane-bound. The cyclooxygenase is rapidly inactivated upon membrane disruption by nonionic detergents or phospholipid degradation with phospholipase A2. It was found that platelet phospholipase A2 preferentially splits off fatty acid with four double bonds. Eicosatetraynoic acid was used to investigate the physiological function of the arachidonate lipoxygenase during collagen-induced aggregation of rat blood platelets. This fatty acid is a more efficient inhibitor of lipoxygenase than of cyclooxygenase. At an inhibitor concentration of 0.6 microgram/ml, platelet aggreation, 12-hydroxyeicosatetraenoic acid production as well as 15-hydroxytryptamine release are completely inhibited, while there is an apparent stimulation of the cyclooxygenase. These results indicate that arachidonate lipoxygenase is essential for irreversible blood platelet aggregation.
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PMID:Study of the two pathways for arachidonate oxygenation in blood platelets. 3 75

Drugs may alter prostaglandin production by acting on the various pathways of arachidonic acid metabolism. The liberation of arachidonic acid from membrane-bound phospholipids, induced by the enzyme phospholipase A2, may be inhibited by mepacrine and the steroidal anti-inflammatory agents. The bio-transformation of the free arachidonic acid, by the enzyme cyclooxygenase, to the unstable endoperoxide intermediates is inhibited by non-steroidal anti-inflammatory agents. Thus, the generation of all the prostaglandin products is prevented. This action can explain the anti-inflammatory, analgesic, antipyretic actions as well as the ulcerogenic properties of these aspirin-like compounds. An alternative metabolic pathway of arachidonic acid, via the lipoxygenase system, can be inhibited by an acetylenic analogue and a newer compound, phenidone. The unstable endoperoxide intermediates can be transformed by blood platelets into the pro-aggregating products, thromboxanes. This pathway can be selectively inhibited by a variety of experimental compounds. Prostacyclin, a potent vasodilator and inhibitor of platelet aggregation is the major product of endoperoxide transformation in blood vessels. Its formation can be inhibited by lipid peroxides. Selective actions on one or more steps in arachidonic acid metabolism can lead to a different profile of the products subsequently generated. Such a diversion of biosynthetic pathways may be an underlying mechanism in certain pathological conditions, perhaps even in dysmenorrhea.
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PMID:Prostaglandin synthetase inhibitors. Drugs which affect arachidonic acid metabolism. 11 64

Rat-liver microsomes were treated with two non-ionic detergents, Triton X-100 and Lubrol WX, with phospholipase A2, or with aqueous acetone solution. The activity of the membrane-bound UDP-glucoronosyltransferase (UDPGT, EC 2.4.1.17) was measured after the treatment with these perturbants. At the same time, modifications of the secondary structure of the microsomal proteins were followed and studied by circular dichroism (CD) spectroscopy. The detergents greatly activated UDPGT, maximally at a 1 mM concentration of either detergent. The maximally activating Triton X-100 treatment did not greatly change the ellipticity of the microsomes at 222 nm ((theta)222), whereas that with Lubrol WX affected the secondary structure of the membrane proteins more strongly. UDPGT activation also occurred in phospholipase A2-treated microsomes. Maximal activation was obtained after 1--5 min of incubation and was stable throughout the experiment. Phospholipase A2 at the ratio of microsomal protein to phospholipase 250 : 1 (w/w) slightly increased (theta)222 after 10 min of incubation and did not change it further even after 30 min of incubation. Treatment of liver microsomes with a 10 : 90 (v/v) aqueous acetone solution removed 90% of the total membrane phospholipids, particularly phosphatidylcholine and phosphatidylethanolamine. The UDPGT activity was decreased in lipid-depleted microsomes, and the enzyme was not reactivated when phosphatidylcholine-lysophosphatidylcholine liposomes were added at a low temperature. An even greater decrease was obtained when the lipid binding was carried out at 37 degree C. Lipid-depleted microsomes had a high (theta)222 associated with a red-shift of 2 nm, indicating partial aggregation of membrane proteins and an increase in the alpha-helical content of the protein after acetone extraction. However, this particular protein structure was partially reversible, since a binding of phospholipids to lipid-depleted microsomes gave a (theta)222 close to that found in control microsomes. The UDPGT activity was not dependent on the secondary structure of the membrane proteins.
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PMID:Effects of membrane perturbants on UDP-glucuronosyltransferase activity in rat-liver microsomes. Circular dichroism studies. 11 96

We investigated the kinetics of mitochondrial ATPase in bovine heart mitochondria and submitochondrial particles upon treatment with phospholipase A2, or upon addition of n-butanol to perturb the lipid protein interactions. The changes observed are the following: (1) Lipid removal or perturbation with butanol is accompanied by loss of ATPase activity with decrease of both V and of the KM for ATP. (2) There are changes of activation energy of ATPase activity at temperatures above the discontinuity normally observed for membrane-bound enzymes in mitochondria. In particular, butanol abolishes the discontinuity, and induces a constant activation energy of about 32 kcal/mol in the range 8--37 degrees C. (3) Butanol modifies the pH dependence of ATPase shifting the pH optimum from around 10 to less alkaline values. The optimum for Mg2+ concentrations is increased by the solvent. (4) Treatment with phospholipase A2 results in a removal of oligomycin-sensitive ATPase, whereas butanol addition prevents oligomycin inhibition of ATPase. (5) In beef heart mitochondria, a spin-labelled analog of the inhibitor, dicyclohexyl carbodiimide, did not show any change in environment upon butanol addition, unlike that found in mitochondria from Saccharomyces cerevisiae.
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PMID:Lipid protein interactions in mitochondria. VII. A comparison of the effects of lipid removal and lipid perturbation of the kinetic properties of mitochondrial ATPase. 15 58

Phospholipase A2 (EC 3.1.1.4) from pig pancreas hydrolyzes phosphatidylglycerol in intact cells and isolated membranes of Acholeplasma laidlawii. Complete degradation of phosphatidylglycerol in intact cells at 37 degrees C does not result in lysis as shown by the retention of intracellular K+ ions and the cytoplasmic glucose-6-phosphatase, as well as the inability to detect activity of membrane-bound intracellular NADH-oxidase. A. laidlawii was grown on linoleic acid. Phospholipase A2 treatment of these cells at 5 degrees C, at which temperature the lipids are still in the liquid-crystalline state, results in a rapid breakdown of 50% of the phosphatidylglycerol. The residual phosphatidylglycerol can be hydrolyzed only at elevated temperatures and at much smaller rates, depending strongly on the incubation temperature. When membranes isolated from these cells are incubated at 5 degrees C, 70% of the phosphatidylglycerol is hydrolyzed immediately. The hydrolysis of the residual 30% is again strongly temperature dependent. Cells were grown on palmitate, elaidate, or oleate to investigate possible effects of the lipid phase transition on the accessibility of phosphatidylglycerol for phospholipase A2. Under conditions in which all the lipid is in the solid state, no hydrolysis occurs. When solid and liquid-crystalline lipid phases coexist, a limited hydrolysis of phosphatidylglycerol can be observed. The results demonstrate the disposition of phosphatidylglycerol in three different pools in the membrane of A. laidlawii. Phospholipase A2 has been used to discriminate between these pools and to estimate the amount of phosphatidylglycerol which is present in the liquid-crystalline phase. The present data, however, do not allow a definite localization of the phosphatidylglycerol pools.
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PMID:Recognition of different pools of phosphatidylglycerol in intact cells and isolated membranes of Acholeplasma laidlawii by phospholipase A2. 19 Oct 65

Phospho-N-acetylmuramoyl-pentapeptide-transferase (UDP-N-acetyl-muramoyl-L-alanyl-D-gamma-glutamyl-L-lysyl-D-alanyl-D-alanine:undecaprenoid-alcohol-phosphate-phospho-N-acetylmuramoyl-pentapeptide-transferase, EC 2.7.8.13) was solubilized by repeated freezing and thawing of crude envelopes of Escherichia coli K12. The solubilized enzyme was partially purified by gel filtration and ion-exchange chromatography. This preparation contained small amounts of phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol but no endogenous lipid substrate, C55-isoprenyl phosphate, could be detected. Some catalytic properties (exchange reaction) of the solubilized enzyme were compared to those of membrane-bound transferase. The transfer activity of the partially purified transferase was restored by the addition of an aqueous lipid dispersion. All the transferase activity was found to become incorporated into the liposomes. Preincubation of the transferase preparation with phospholipase A2 or D strongly reduce both exchange and transfer activity. This suggests that phospholipids sensitive to phospholipases are necessary for the enzymatic reaction. Different effects of some neutral detergents on the exchange activity were reported.
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PMID:Phospho-N-acetylmuramoyl-pentapeptide-transferase of Escherichia coli K12. Properties of the membrane-bound and the extracted and partially purified enzyme. 21 12

The subcellular distribution of oleoyl-CoA:1-acyl-sn-glycero-3-phosphocholine acyltransferase (E.C.2.3.1.23) in cultured swine aorta endothelial cells and smooth muscle cells was investigated. Isolated membrane pellets were centrifuged through linear sucrose gradients, and the distributions of the activities of seven membrane-bound enzymes were measured. The distribution of acyltrasferase activity was similar to that of the endoplasmic reticulum enzymes. Gradient fractions which contained intact mitochondria had very low activities of acyltransferase. Experiments using mixed fractions and measurements made under conditions which inhibit phospholipase A2 showed that no acyltransferase activity from this location was masked by competing activities. When membranes were treated with digitonin, plasma membranes specifically increased in density, facilitating their separation from endoplasmic reticulum membranes. The plasma membranes were free of acyltransferase activity. We conclude that in cultured swine arterial smooth muscle and endothelial cells, acyltransferase is located primarily in the endoplasmic reticulum.
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PMID:Distribution of membrane marker enzymes in cultured arterial endothelial and smooth muscle cells. The subcellular location of oleoyl-CoA:1-acyl-sn-glycero-3-phosphocholine acyltransferase. 71 55

Exposure of rabbit pulmonary arterial smooth muscle cells to hydrogen peroxide cause dose-dependent stimulation of [14C] arachidonic acid (AA) release and enhancement of the cell membrane-associated phospholipase A2 activity as well as of the cell membrane-bound serine esterase activity tested against synthetic substrate p-tosyl-L-arginine methyl ester. While pretreatment of cells with serine protease inhibitors, viz. phenyl methyl sulphonyl fluoride, diisopropyl fluorophosphate and alpha-1-proteinase inhibitor, and antioxidant vitamin E prevents H2O2 stimulation of AA release and the cell membrane-bound serine esterase and PLA2 activities, that with actinomycin D and cycloheximide is devoid of any effect on H2O2 caused stimulation of AA release and the smooth muscle cell membrane associated serine esterase and PLA2 activities. Treatment of the smooth muscle cell membrane suspension with the serine protease trypsin markedly stimulates PLA2 activity. These results suggest that on exposure to H2O2 the smooth muscle cell membrane-bound serine esterase plays an important role in stimulating the cell membrane associated PLA2 activity thereby resulting in an increase in AA release.
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PMID:Role of serine esterase in hydrogen peroxide-mediated activation of phospholipase A2 in rabbit pulmonary arterial smooth muscle cells. 129 64

Annexins constitute a family of cytosolic, water soluble proteins, which bind to negatively charged phospholipids in a calcium-dependent manner. They display structural and functional features of both soluble and integral membrane proteins. The annexins face the hydrophilic as well as the hydrophobic phase (Janus-faced proteins) and mediate ion transport in vitro. We present the refined structure and molecular model of annexin V at 2.0 A resolution. The molecule is almost entirely alpha-helical, and each of the four repeats of annexin V is folded into a compact domain of similar structure. The four domains are arranged in an almost planar, cyclic array. In the center of the molecule, one can find a prominent hydrophilic pore, which we associate with the calcium-selective channel found in annexin V. Annexin V has an overall flat, slightly curved shape with two faces, one convex and one concave. The three calcium binding sites Ca1 to Ca3, all located at the convex face of the molecule, are assumed to be phospholipid binding sites, as suggested by their structural similarity to the calcium site of phospholipase A2. Soluble and membrane-bound annexin have closely similar structures, as shown by electron microscopic analysis. Several other observations provide evidence that the membrane-anchoring region of the annexin V molecule is located on the convex face. In the last part of this article, the electrophysiology of the annexins is described. Ion permeation occurs in discrete conductance states and is regulated by voltage across the membrane. A model for the annexin V-membrane interaction, the ion channel formation, and the ion conduction pathway is proposed.
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PMID:Annexin V-crystal structure and its implications on function. 138 18

Pyrularia thionin is a strongly basic bioactive peptide of 47 amino acids isolated from nuts of Pyrularia pubera. It is hemolytic, cytotoxic and activates an endogenous phospholipase A2 in 3T3 cells. Earlier studies have shown that the cardiotoxin from Naja naja kaouthia has similar activities and binds to the same site as Pyrularia thionin. Since the peptides appear to bind to the phospholipids of cell membranes to elicit their cellular responses, the effect of modifying the electrostatic environment was studied by separately adding phosphate ion and Ca2+, and by removing Ca2+ from the membrane by treatment with EGTA. Analysis of erythrocyte hemolysis for both Pyrularia thionin and cardiotoxin shows that the reactions follow Michaelis-Menten kinetics, with the peptides serving as the substrate. The basal rate of hemolysis in physiological saline is markedly increased by the addition of phosphate in the 5-10 mM range and also by removing membrane-bound Ca2+ by incubation of the cells with 10 mM EGTA. These treatments do not change the apparent K(m) values, but increase the V(max), indicating that more binding sites are made available by these treatments. On the other hand, added Ca2+ in the 5-10 mM range competitively inhibits the reaction by inhibiting the binding of the peptide to the membrane.
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PMID:Effect of calcium and phosphate ions on hemolysis induced by Pyrularia thionin and Naja naja kaouthia cardiotoxin. 150 89


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