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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)

A membrane fraction enriched in endoplasmic reticulum was prepared from rat parotid glands by using sucrose-gradient centrifugation. The fraction showed a 10-fold increase in specific activity of NADPH: cytochrome c reductase activity over that of tissue homogenates and minimal contamination with plasma membranes or mitochondria. The endoplasmic reticulum fraction possessed both Mg2+ -stimulated ATPase as well as Ca2+, Mg2+-ATPase [( Ca2+ + Mg2+)-stimulated ATPase]activity. The Ca2+, Mg2+-ATPase required 2-5 mM-Mg2+ for optimal activity and was stimulated by submicromolar concentrations of free Ca2+. The Km for free Ca2+ was 0.55 microM and the average Vmax. was 60 nmol/min per mg of protein. The Km for ATP was 0.11 mM. Other nucleotides, such as GTP, CTP or ADP, could not substitute for ATP in supporting the Ca2+-activated nucleotidase activity. Increasing the K+ concentration from 0 to 100 mM caused a 2-fold activation of the Ca2+, Mg2+-ATPase. Trifluoperazine, W7 [N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide] and vanadate inhibited the enzyme. The concentration of trifluoperazine and vanadate required for 50% inhibition of the ATPase were 52 microM and 28 microM respectively. Calmodulin, cyclic AMP, cyclic AMP-dependent protein kinase and inositol 1,4,5-trisphosphate had no effect on the ATPase. The properties of the Ca2+, Mg2+ -ATPase were distinct from those of the Mg2+-ATPase, but comparable with those reported for the parotid endoplasmic-reticulum Ca2+-transport system [Kanagasuntheram & Teo (1982) Biochem. J. 208, 789-794]. The results suggest that the Ca2+, Mg2+-ATPase is responsible for driving the ATP-dependent Ca2+ accumulation by this membrane.
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PMID:The (Ca2+ + Mg2+)-stimulated ATPase of the rat parotid endoplasmic reticulum. 294 71

The lipid composition and fluidity of plasma membranes have been studied at different stages of liver regeneration (4, 15 and 24 h after surgery). The phospholipid and fatty acid composition is not modified, whereas the cholesterol/phospholipid ratio is lower with respect to control membranes. The modification of the physical properties of the membranes has been studied directly by EPR analysis and indirectly by temperature dependence and cooperativity of some membrane-bound enzymes (Mg2+-ATPase, (Na+ + K+)-ATPase and 5'nucleotidase). Surgical operation or anaesthesia alone causes an early increase in fluidity; such an effect appears to be markedly reduced at a later stage. There seems to be a marked effect of regeneration on plasma membrane fluidity 15 h after partial hepatectomy when several parameters--surface fluidity, cholesterol/phospholipid ratio, and 5'-nucleotidase activity in the presence of concanavalin A -- are modified and indicate an increase in membrane fluidity. It is suggested that this modification of membrane properties could be related to the proliferative process.
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PMID:Plasma membrane changes associated with rat liver regeneration. 624 90

Synaptic plasma membrane (SPM)-bound, extracellular-facing (ecto) ATPases are Mg2+- or Ca2+-activated enzymes that regulate the synaptic levels of the excitatory neurotransmitter ATP and provide ADP for the further ecto-nucleotidase-mediated production of the inhibitory neuromodulator adenosine. The present results show that low concentrations (IC50 = 4 microM) of the lipid peroxidation product 4-hydroxynonenal (HNE) inhibited up to about 80% of the ecto-ATPase activity of SPM purified from rat brain cerebral cortex. In contrast, low concentrations of HNE did not inhibit the activity of the "intracellular"-facing Na+, K+, Mg2+-ATPase. In addition, the inhibition of SPM ecto-ATPase activity by HNE was largely irreversible and pH-dependent. Furthermore, structure-activity studies demonstrate that inhibition was dependent on the presence of the reactive functional groups of HNE. These findings suggest that HNE selectively inhibits SPM ecto-ATPase activity by a mechanism that may involve the covalent modification of functionally-critical nucleophilic amino acids. It is proposed that inhibition of SPM ecto-ATPase activity could contribute to the mechanisms by which lipid peroxidation and HNE formation promote excitotoxicity.
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PMID:The lipid peroxidation product 4-hydroxynonenal potently and selectively inhibits synaptic plasma membrane ecto-ATPase activity, a putative regulator of synaptic ATP and adenosine. 1049 19