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At least 1,027 records · Page 57Linked to original sources
PubMed1993

Phospholipase A2-induced stimulation of A549 lung adenocarcinoma cell line proliferation.

Phospholipase A2 (PLA2) activity was found in the cytosolic fraction of the A549 human lung adenocarcinoma line. This PLA2 had a molecular mass of approximately 70 kDa as assessed by gel filtration chromatography and required submicromolar concentrations of calcium concentrations for optimal activity. These characteristics are consistent with the cytosolic PLA2 recently reported in other cell types, such as U937 cells. We have now demonstrated that A549 cell PLA2 (PLA2 activity: 1 unit/ml) partially purified by gel filtration stimulated proliferation of A549 cells by 50% after 3 days of culture. Similarly, porcine pancreatic PLA2 (0.1 unit/ml) also promoted proliferation of A549 cell cultures by 42%. Furthermore, A549 cell PLA2 stimulated prostaglandin E2 release (approx. 7-fold increase). Both PLA2s lost activity when treated with p-bromophenacyl bromide. Neither porcine pancreatic PLA2 nor A549 cell PLA2 reversed the inhibitory activities of dexamethasone and indomethacin on cell growth. These results suggest that both of these PLA2s stimulate A549 cell growth, and that this is likely to be mediated by increased eicosanoid production.

Acetophenones↗
PubMed1994

Effect on human platelet aggregation of phospholipase A2 purified from Heloderma horridum (beaded lizard) venom.

By means of gel filtration, ionic exchange chromatography and DEAE-column HPLC, an acidic phospholipase A2 (PLA2) was purified from beaded lizard (Heloderma horridum) venom. The purified PLA is a single-chain polypeptide, consisting of about 163 amino acid residues with a molecular mass of 19,000 Da as calculated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and amino acid analysis. HHV-PLA showed a rather specific inhibitory effect on platelet aggregation induced by U46619 and epinephrine in human platelet-rich plasma in a dose- and time-dependent manner, whereas it had little effect on collagen- and ADP-induced aggregation. ATP-release reaction induced by various agonists were dose- and time-dependently inhibited by HHV-PLA, even though platelet aggregation was apparently not affected in human washed platelets. When HHV-PLA was chemically modified with p-bromophenacyl bromide, both of its enzymatic activity and antiplatelet activity were lost. Furthermore, exogenous lysophosphatidylcholine and HHV-PLA treated phosphatidylcholine inhibited platelet aggregation induced by U46619 in human washed platelets. In conclusion, PLA enzyme from H. horridum venom inhibits exclusively U46619- or thromboxane-induced platelet aggregation of human platelet-rich plasma probably by virtue of their PLA enzymatic activity on plasma phospholipids, converting phospholipids (e.g., phosphatidylcholine) into lysophospholipids, which in turn interfere with the coupling of TXA2 receptor and its signalling transduction system.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1980

Further characterization and N-terminal sequence of cobra venom phospholipase A2.

N-terminal amino acid sequence data on cobra venom phospholipase A2 (Naja naja naja) demonstrate the absence of histidine at positions 10 and 20, in contrast to most other Naja enzymes. The presence of three tryptophans was demonstrated by p-toluenesulfonic acid hydrolysis, and the location of two of these at positions 18 and 19 parallels other Naja phospholipase A2 sequences. Based on the amino acid composition of the enzyme, the theoretical E278 0.1% should be 2.2, which is consistent with dry weight determinations, refractometry and amino acid analysis. Unusually high reactivity of the enzyme toward the protein assay of Lowry et al. gives an erroneously low E278 0.1% value of 1.45 when compared to bovine serum serum albumin as a protein standard. Using an E278 0.1% of 2.2, this enzyme is inactivated by the active site reagent p-bromophenacyl bromide with a stoichiometry of 1 mol reagent per mol enzyme. Chromatography on Affi-Gel Blue provides further purification of this phospholipase A2.

Acetophenones↗
PubMed1984

Possible involvement of cyclooxygenase products in the actions of platelet-activating factor and of lipoxygenase products in the vascular effects of epinephrine in perfused rat liver.

Platelet-activating factor (PAF) stimulates glycogenolysis and induces vasoconstriction in perfused rat liver. The effect of PAF was rapid but transient and it was blocked by indomethacin and bromophenacyl bromide which suggests a role of cyclooxygenase metabolites in its action. The homologous desensitization of glycogenolysis produced by PAF and the sensitivity of its actions to inhibitors of cyclooxygenase and phospholipase A2 markedly differentiate the mechanism of action of this agent with that of alpha 1-adrenergic agents, vasopressin or angiotensin II. No effect of PAF in isolated hepatocytes was observed which suggest that cells other than hepatocytes could be involved in its action in perfused liver. In addition nordihydroguaiaretic acid and bromophenacyl bromide abolished the vascular effect (but not the glycogenolysis) produced by epinephrine which suggest a role for lipoxygenase products in this effect.

Acetophenones↗
PubMed1984

Activation of cyclic AMP-dependent protein kinase in macrophages.

The activity of cyclic AMP-dependent protein kinase (cyclic AMP-PK) was significantly higher (P less than 0.001) in thioglycollate-elicited than in resident rat peritoneal macrophages. The activity ratio of the enzyme (its activity in the absence of added cyclic AMP divided by that in the presence of 5 microM cyclic AMP) was similar in the two cell types. The divalent ion ionophore A23187 induced a rapid increase in the activity ratio of cyclic AMP-PK in both macrophage types. This effect was blocked by pretreating the cells with indomethacin or aspirin (inhibitors of cyclo-oxygenase) and bromo-phenacyl bromide (an inhibitor of phospholipase A2), implicating the synthesis of a prostanoid as an intermediary step. Prostaglandin (PG) E2, 8-bromo cyclic AMP and cholera toxin, all of which inhibit chemiluminescence and/or PG formation in macrophages, increased the activity ratio of cyclic AMP-PK in these cells. We propose that the activation of cyclic AMP-PK plays a central role in the response of macrophages to both endogenously-generated and exogenously added PGE.

Acetophenones↗
PubMed1985

Stimulation of hepatic glycogenolysis by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) via cyclooxygenase products.

12-O-Tetradecanoyl-phorbol-13-acetate (TPA) stimulates glycogenolysis in perfused rat liver. The effect of TPA was blocked by indomethacin and bromophenacyl bromide. The effect of TPA on glucose output was transient in spite of the continuous presence of the phorbol ester in the perfusion medium. Addition of platelet activating factor (PAF) after the effect of TPA did not stimulate glycogenolysis. In contrast, vasopressin was able to stimulate glucose output under these conditions. Interestingly, as previously reported, PAF produced also transient stimulation of glycogenolysis; the addition of TPA after the effect of PAF had declined, was also unable to increase glucose output by the liver. It is suggested that both PAF and TPA stimulate hepatic metabolism through the generation of cyclooxygenase products.

Acetophenones↗
PubMed1985

Comparison of sulfide oxygenation mechanism for liver microsomal FAD-containing monooxygenase with that for cytochrome P-450.

Mechanistic mode for the oxygenation of sulfides with the pig liver microsomal FAD-containing monooxygenase(EC 1.14.13.8) has been conveniently distinguished from that with the phenobarbital induced liver microsomal cytochrome P-450 by analyzing products of the oxygenation of phenacyl phenyl sulfide. Upon oxygenation of phenacyl phenyl sulfide, the FAD-containing monooxygenase gave solely phenacyl phenyl sulfoxide in contrast to the cytochrome P-450 promoted oxygenation which is known to give substantial amounts of C-S bond fission products. The observation suggests that the oxygenation of sulfide with FAD-containing monooxygenase involves the nucleophilic attack of the divalent sulfur on the reactive oxygen atom involved at the enzyme active site, namely electrophilic oxygenation of sulfide, though the oxygenation with the cytochrome P-450 is initiated by a single electron transfer from the sulfide to the enzyme active species.

Acetophenones↗