Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The behaviour of Ca2+ ATPase activity in relation to Ca2+ transport process was studied under different experimental conditions in canine cardiac microsomal fraction predominantly containing sarcoplasmic reticulum. The total Ca2+ concentration required for half maximal activation (Ka) of microsomal Ca2+ ATPase and Ca2+ uptake did not differ significantly, unless 0.1 mmol/l EGTA was present in the incubation media. Pretreatment of cardiac microsomes with membrane disruptive agents like phospholipase A, trypsin as well as deoxycholate strongly increased (2-3 fold) Ca2+ ATPase activity but uptake rate of Ca2+ declined. Only in phospholipase C and beta-glucuronidase pretreatment, a parallel decrease of Ca2+ ATPase and uptake was observed. In presence of excess (free)Ca2+ (greater than 10 mumol/l) both Ca2+ ATPase as well as Ca2+ uptake were inhibited, however, Ca2+ binding process remained unaltered. Likewise, low pH completely altered the relation between Ca2+ binding and ATPase activity; whereas Ca2+ ATPase was inhibited, Ca2+ binding did not change. Our present data provide evidence for some cellular factors that may be involved in producing uncoupling of microsomal Ca2+ ATPase from Ca2+ accumulation process that was previously observed in various pathological situations.
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PMID:Behaviour of cardiac microsomal Ca2+ pump under conditions that may simulate pathological situations. 316 76

Guinea-pig gastric mucosal cells isolated by collagenase and pronase digestion were used to study the release of prostanoids prostaglandin I2 (PGI2; measured as 6-keto PGF1 alpha), PGE2, PGF2 alpha and thromboxane A2 (TXA2; measured as TXB2). Lysophosphatide acyltransferase (LAT) and phospholipase A2 (PLA2) were measured in the microsomal fraction of isolated but not separated gastric cells and isolated and enriched parietal and mucous cells. In all cell preparations PLA2 activity was approximately 5 times higher than that of LAT. Acid-activated omeprazole inhibited LAT in a concentration-dependent manner with similar IC50 values in gastric, parietal and mucous cells. It had no effect on PLA2. Gastric cells constantly produced PGI2, PGE2, PGF2 alpha and TXA2. The main prostaglandins released were PGI2 and PGE2. PGF2 alpha and TXA2 were released in smaller quantities. Omeprazole dissolved in polyethylene glycol 400 (PEG) pH 2 inhibited spontaneous PGI2 release in a concentration-dependent manner with an IC50 of 14.3 +/- 4.8 microM. Only concentrations as high as 100 microM produced a significant reduction in PGE2 release by 60%. No significant changes could be detected in the spontaneous release of PGF2 alpha and TXA2. Omeprazole dissolved in PEG pH 7 had no effect on PGI2 release except at 100 microM which led to an insignificant decrease by 40%. These data suggest that omeprazole beyond its inhibitory effect on parietal cell K+/H+-ATPase also affects gastric mucosal prostanoid formation and release. The inhibitory effect on PGI2 does not support the view that omeprazole protects the gastric mucosa by increasing prostanoid formation.
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PMID:Effect of omeprazole on eicosanoid formation in and release from guinea-pig gastric mucosal cells. 329 28

Contracture responses to cardiotoxin (CTX) from Naja naja kaouthia venom were investigated in rat and human skeletal muscle of similar fiber type distribution to determine species differences in mechanism of action. Rat diaphragm strips and human vastus lateralis preparations were directly stimulated in a tissue bath. The calcium dependence of toxin action, synergism between CTX and phospholipase A2 (PLA2) activity and roles of Na+ + K+-ATPase activity and the sarcoplasmic reticulum Ca2+ stores in contracture induction were examined. The threshold of contracture to CTX was decreased in human and rat muscle when Sr2+ was substituted for Ca2+ in the bathing medium. In rat, but not in human muscle the threshold of contracture to CTX was decreased in a medium in which Ca2+ had been omitted. The decrease in contracture threshold may relate to toxin binding. The maximum height of contracture for preparations from humans, but not for those from rats was considerably depressed in a medium in which Ca2+ had been omitted. Exogenously added bee venom PLA2 acts synergistically with CTX in skeletal muscle in a manner similar to that in erythrocytes. Ouabain (100 microM) did not elicit contractures in any of the media tested nor affect CTX-induced contractures in Sr2+-containing medium. Dantrolene antagonized CTX-induced contractures, suggesting a role for Ca2+ derived from the sarcoplasmic reticulum in CTX action. The species difference in CTX action may reflect differences in the relative contribution of Ca2+ from the sarcolemma and sarcoplasmic reticulum to the contracture.
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PMID:Contracture induction by snake venom cardiotoxin in skeletal muscle from humans and rats. 343 97

The beta-bungarotoxin-induced depolarization of the synaptosomal plasma membrane monitored by the efflux of 86Rb+ is potentiated by raising the albumin in the incubation, is Ca2+-dependent and is due neither to inhibition of the (Na+ + K+)-dependent ATPase nor to activation of the voltage-dependent Na+ channel. Occupancy of the beta-bungarotoxin-binding site by dendrotoxin inhibits partially the action of beta-bungarotoxin. The efflux of 86Rb+ is parallelled by a release of lactate dehydrogenase from the synaptosome, and the two processes are maximal with 2 nM-toxin. Digitonin induces a release of 86Rb+ and lactate dehydrogenase closely similar to that seen with beta-bungarotoxin. It is concluded that the toxicity of beta-bungarotoxin for mammalian nerve terminals can be largely accounted for by specific site-directed phospholipase A2-induced permeabilization of the plasma membrane.
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PMID:The mechanism of action of beta-bungarotoxin at the presynaptic plasma membrane. 395 50

The role of lipids of the sarcotubular membranes in their Ca(++) uptake and Mg-ATPase activities was investigated. Treatment of the membranes with phospholipase C inhibits both processes. Treatment with phospholipase A and phospholipase D, which results in massive hydrolysis of the sarcotubular phospholipids, does not inhibit either the Ca(++) uptake or the Mg-ATPase activities, nor does treatment with the polyene antibiotics affect these processes. Essential fatty acid deficiency alters sarcotubular membrane lipids; they contain much less stearic, linoleic, and arachidonic acids and much more oleic and eicosatrienoic acids than normally, but do not lose the ability to actively sequester Ca(++). It is concluded that neither nonpolar lipids nor the nonpolar regions of polar lipids are involved in Ca(++) sequestering and Mg-ATPase activities of the sarcotubular membranes. Of the polar components, the phosphoryl moiety of the phospholipids is required for both activities. However, the phosphoryl group appears to be required for the maintenance of the membranous structure necessary for Ca(++) sequestration rather than serving specifically in the active transport process. That treatment with phospholipase D, which results in the conversion of much of the sarcotubular phospholipid from a dipolar to an anionic structure, does not affect Ca(++) uptake activity is a most remarkable finding.
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PMID:Relation of lipid structure of sarcotubular vesicles to Ca++ transport activity. 423 45

Membranes of Micrococcus lysodeikticus possess antigens which are distinct from other cellular components such as cytoplasm, ribosomes, and cell walls. Only a few (two to three) components are found when dissociated membranes are examined by immunodiffusion and immunoelectrophoresis techniques. Membranes treated with 0.3% sodium dodecyl sulfate, 0.3% Triton X-100, trypsin, phospholipase A or C, or by sonic oscillation at pH 9.0, all showed the same pattern (three major bands) when examined against membrane antisera by immunoelectrophoresis. Immunological analysis of fractions isolated by sucrose gradient centrifugation or by polyacrylamide gel electrophoresis suggests that individual components cross-react. Antibodies to adenosine triphosphatase (EC 3.6.1.3) and fast-moving component are not removed by absorption with protoplasts. Removal of antibody to one of the membrane antigens by protoplast absorption indicated a surface location. Glutaraldehyde fixation of protoplasts resulted in the loss of membrane antigens detectable by immunodiffusion.
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PMID:Immunological properties of Micrococcus lysodeikticus membranes. 425 Jun 11

The effect of phospholipids on Triton X-100 solubilized (Ca2+ + Mg2+)-ATPase from human erythrocyte membranes has been examined. The enzyme activity was increased by phosphatidylinositol, phosphatidylserine, and phosphatidic acid at both low (2 micrometer) and high (65 micrometer) free Ca2+ concentrations, while phosphatidylcholine had little effect and phosphatidylethanolamine and cardiolipin inhibited the (Ca2+ + Mg2+)-ATPase activity at all Ca2+ concentrations studied. The diacylglycerol, diolein, inhibited the enzyme at high, but not low, Ca2+ concentrations. Low concentrations of phospholipase A2 (1-2 international units) also activated the solubilized enzyme, at least in part by releasing free fatty acids, as the activation was mimicked by oleic acid (1-2 mumol/mg protein) and was abolished by fatty acid depleted bovine serum albumin. The combined activation by saturating levels of phosphatidylserine and calmodulin was additive at 6.5 mM MgCl2, and probably occurred at distinct sites on a regulatory component of the enzyme. The activation by both effectors was antagonized by MgCl2 at similar concentrations. Analysis of various models suggested that phosphatidylserine had two effects on (Ca2+ + Mg2+)-ATPase activity. First, a low Ca2+ affinity form of the enzyme was converted to a high Ca2+ affinity form, which was more sensitive to Ca2+ inhibition. Second, it increased the turnover of the enzyme, probably by enhancing its dephosphorylation, which was mimicked in this study by the Ca2+-dependent p-nitrophenylphosphatase partial reaction.
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PMID:Phospholipid and calmodulin activation of solubilized calcium-transport ATPase from human erythrocytes: regulation by magnesium. 612 Jul 52

Non-neurotoxic phospholipase A2 of Formosan cobra venom possessed higher hydrolytic activity on phosphatidylcholine vesicles and also had higher inhibitory action on Na+-K+-ATpase and Mg2+-ATPase of the rat synaptic membrane than neurotoxic beta-bungarotoxin of Formosan Krait Venom. Na+-K+-ATPase was more susceptible than Mg2+-ATPase to the inhibitory action of toxins, especially in the presence of Triton X-100. The inhibition of ATPases by toxins followed the Michaelis-Menton equation. It is interesting that various phospholipids and ions influenced phospholipase A2 and beta-bungarotoxin inhibition of ATPases. Sphingomyelin antagonized phospholipase A4 more profoundly than beta-bungarotoxin, while egg lecithin had the reverse effect. Both phosphatidylethanolamine and phosphatidylserine protected Na+-K+-ATPase from the inhibitory action of phospholipase A2 but not that of beta-bungarotoxin. High K+ (30 mM) did not affect, while Ca2+ (0.2 mM) decreased, the inhibitory action of phospholipase A2 on Na+-K+-ATPase; in contrast, high K+ reversed, and Ca2+ increased, that of beta-bungarotoxin. These findings imply that phospholipase A2 and beta-bungarotoxin may have different substrate specificities and prefer different conformational states of the membrane for binding. This may explain, at least in part, why beta-bungarotoxin is neurotoxic, while phospholipase A2 is not.
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PMID:Effects of beta-bungarotoxin and phospholipase A2 from Naja naja atra snake venom on ATPase activities of synaptic membranes from rat cerebral cortex. 612 64

The artificial insertion of increasing amounts of unsaturated fatty acids into human erythrocyte membranes modulated ATPase activities in a biphasic manner, depending on the number and position of double bonds, their configuration, and the chain length. Uncharged long-chain fatty acid derivatives with double bonds and short-chain fatty acids were ineffective. Stearic acid stimulated Na+ K+-ATPase only. Anionic and non-ionic detergents and alpha-lysophosphatidylcholine failed to stimulate ATPase activities at low, and inhibited them at high concentrations. Mg2+-AtPase activity was maximally enhanced by a factor of 2 in the presence of monoenoic fatty acids; half-maximal stimulation was achieved at a molar ratio of cis(trans)-configurated C18 acids/membrane phospholipid of 0.16 (0.26). Na+K+-ATPase activity was maximally augmented by 20% in the presence of monoenoic C18 fatty acids at 37 degrees C. Half-maximal effects were attained at a molar ratio oleic (elaidic) acid/phospholipid of 0.032 (0.075). Concentrations of free fatty acids which inhibited ATPases activities at 37 degrees C were most stimulatory at reduced temperatures. At 10 degrees C, oleic acid increased Na+K+-ATPase activity fivefold (molar ratio 0.22). Unsaturated fatty acids simulated the effects of calmodulin on Ca2+-ATPase of native erythrocyte membranes (i.e., increase of Vmax from 1.6 to 5 mumol PO43- . phospholipid-1 . hr-1, decrease of K'Ca from 6 microM to 1.4-1.8 microM). Stearic acid decreased K'Ca (2 microM) only, probably due to an increase of negative surface charges. A stimulation of Mg2+-ATPase, Na+K+-ATPase, and Ca2+-ATPase could be achieved by incubation of the membranes with phospholipase A2. An electrostatic segregation of free fatty acids by ATPases with ensuing alterations of surface charge densities and disordering of the hydrophobic environment of the enzymes provides an explanation of the results.
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PMID:Modulation of ATPase activities of human erythrocyte membranes by free fatty acids or phospholipase A2. 612 96

The cytotoxic action of the S component of leukocidin from Staphylococcus aureus on rabbit polymorphonuclear leukocytes was supported by the following observations, (i) Leukocytes displayed a large chemotactic response to the S component (10(-10) M) as well as to the chemotactic factor N-formylmethionylleucylphenylalanine (10(-11) M). (ii) The S component stimulated high levels of phospholipase A2 activity in the cell membranes, with concomitant synthesis and release of prostaglandins. (iii) Uptake of 45Ca into leukocytes exposed to the S component was about double the rate of uptake into untreated cells. The increased 45Ca uptake into the cells was not inhibited by trifluoperazine and ruthenium red. (iv) Indomethacin and alloxazine, which had no effects on the binding of the S component to the cells, attenuated markedly the stimulation of phospholipase A2 activity, the syntheses of prostaglandins, and the increased uptake of 45Ca caused by the S component. The F component of leukocidin, bound to rabbit leukocytes with the aid of the S component, rapidly induced complete release of 86Rb from preloaded leukocytes. This release resulted from stimulation of ouabain-insensitive (Na+ + K+)-adenosine triphosphatase activity and inhibition of cyclic AMP-dependent protein kinase.
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PMID:Mode of action of staphylococcal leukocidin: effects of the S and F components on the activities of membrane-associated enzymes of rabbit polymorphonuclear leukocytes. 627 2


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