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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phospholipid and fatty acid composition and role of phospholipids in enzyme and transport function of gastric (H+ + K+)-ATPase vesicles was studied using phospholipase A2 (bee venom). The composition (%) was phosphatidyl-choline (PC) 33%; sphingomyelin (sph) 25%; phosphatidylethanolamine (PE) 22%; phosphatidylserine (PS) 11%; and phosphatidylinositol (PI) 8%. The fatty acid composition showed a high degree of unsaturation. In both fresh and lyophilized preparations, even with prolonged incubation, only 50% of phospholipids were hydrolyzed, but the amount of PE and PS disappearing was increased following lyophilization. There was a marked decrease in K+-ATPase activity (75%) but essentially no loss of the associated K+ p-nitrophenyl phosphatase was found. ATPase activity could be largely restored by various phospholipids (PE greater than PC greater than PS). There was also an increase in Mg2+-ATPase activity, partially reversed in fresh preparations by the addition of phospholipids (PE greater than PS greater than PC). Proton transport activity of the preparation was rapidly inhibited, initially due to a large increase in the HCl permeability of the preparation. Associated with these enzymatic and functional changes, the ATP-induced conformational changes, as indicated by circular dichroism spectra were inhibited.
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PMID:Effect of phospholipase A2 on purified gastric vesicles. 4 34

The phospholipid requirement for Ca2+-stimulated, Mg2+-dependent ATP hydrolysis (Ca2+/Mg2+-ATPase) and Mg2+-stimulated ATP hydrolysis (Mg2+-ATPase) in rat brain synaptosomal membranes was studied employing partial delipidation of the membranes with phospholipase A2 (Hog pancreas), phospholipase C (Bacillus cereus) and phospholipase D (cabbage). Treatment with phospholipase A2 caused an increase in the activities of both Ca2+/Mg2+-ATPase and Mg2+-ATPase whereas with phospholipase C treatment both the enzyme activities were inhibited. Phospholipase D treatment had no effect on Ca2+/Mg2+-ATPase but Mg2+-ATPase activity was inhibited. Inhibition of Mg2+-ATPase activity after phospholipase C treatment was relieved with the addition of phosphatidylinositol-4,5-bisphosphate (PIP2) and to a lesser extent with phosphatidylinositol-4-phosphate (PIP) and phosphatidylcholine (PC). Phosphatidylserine (PS), phosphatidic acid (PA), PIP and PIP2 brought about the reactivation of Ca2+/Mg2+-ATPase. Phosphatidylinositol (PI) and PA inhibited Mg2+-ATPase activity. Kms for Ca2+ (0.47 microM) and Mg2+ (60 microM) of the enzyme were found to be unaffected after treatment with the phospholipases.
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PMID:Phospholipid requirement of Ca2+-stimulated, Mg2+-dependent ATP hydrolysis in rat brain synaptic membranes. 294 70

The bee and cobra venom phospholipases A2 as well as partially acetylated cobra venom phospholipase A2 are studied for their effect on phospholipid composition of synaptosomes and their Mg2+- and Na+,K+-ATPase activity. It is established that these phospholipases induce the splitting of phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine, inhibition of the Na+,K+-ATPase activity and activation of Mg2+-ATPase. Bee venom phospholipase A2 is more effective than cobra venom phospholipase A2, the both phospholipases splitting phosphatidylethanolamine most intensively. The ATPase activity may be partially or completely restored by exogenic phosphatidylcholine and phosphatidylserine; exogenic phosphatidylethanolamine is not efficient in this respect.
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PMID:[Effect of phospholipases A2 from bee and cobra venom on the phospholipid composition and Na+-,K+-ATPase activity of synaptosomes]. 300 36

Treatment of liver plasma membranes with phospholipase A2 or high doses of concanavalin A enhances the activity of Mg2+ATPase assayed at temperatures greater than 30 degrees C. The effects of the two treatments are not additive. Both the removal of phospholipids and binding of the lectin increase the degree of polarization of fluorescence of the lipid-soluble fluorophores, diphenylhexatriene and beta-parinaric acid, suggesting that decreased lipid fluidity may activate Mg2+-ATPase. In fact modification of lipid fluidity by reconstitution of phospholipase-treated membranes with phosphatidylcholines of defined fatty acid composition or by addition of cis-vaccenic acid showed a strong inverse correlation between Mg2+ATPase activity and lipid fluidity as monitored by fluorescence polarization. However, despite the ability of concanavalin A to nonspecifically order membrane lipid, its effect on Mg2+ATPase is apparently not mediated in this manner because other enzyme-activating lectins such as Ricinus communis agglutinin and wheat germ agglutinin are without effect on lipid fluidity. The facts that lectins of lower valency than tetravalent native concanavalin A such as divalent succinyl concanavalin A are far less effective in activating the enzyme and that paraformaldehyde treatment also activates suggests that cross-linking of membrane proteins is responsible. Hence, the diminution in activity of this membrane enzyme due to the disordering effect of heat in the physiological temperature range can be counteracted by isothermally increasing the order of either membrane lipid or protein.
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PMID:Ordering of bulk membrane lipid or protein promotes activity of plasma membrane Mg2+ATPase. 610 59

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