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

---

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.
...
PMID:The (Ca2+ + Mg2+)-stimulated ATPase of the rat parotid endoplasmic reticulum. 294 71

Fodrin, a non-erythrocyte spectrin-like protein, has been purified from bovine brain and found to be phosphorylated by the cyclic AMP-dependent protein kinase with a maximal stoichiometry of 1.02 +/- 0.06 mol of phosphate/mol of fodrin dimer (n = 4). This phosphorylation was not affected by the presence of actin and calmodulin. The phosphorylation of fodrin was found to occur exclusively at serine residues on the beta subunit. Two-dimensional thin layer electrophoresis and chromatography of a tryptic digest of phosphorylated fodrin showed one major phosphopeptide and a few minor ones. We have previously reported that nonphosphorylated fodrin is capable of stimulating the smooth muscle actomyosin Mg2+-ATPase by 50-70% under a well-defined set of conditions such as a critical fodrin concentration and an optimal preincubation time (Wang, C., Ngai, P.K., Walsh, M.P., and Wang, J.H. (1987) Biochemistry 24, 1110-1117). We now report that phosphorylation of fodrin completely eliminates this stimulatory effect. However, phosphorylation of fodrin was able to compete with nonphosphorylated fodrin to result in the abolition of the stimulatory effect. Similarly, nonphosphorylated fodrin could overcome the inhibitory effect created by phosphorylated fodrin. The present results support the suggestion that the stimulation of the smooth muscle actomyosin Mg2+-ATPase by fodrin may be a physiological phenomenon and cyclic AMP may serve as a regulator for this effect.
...
PMID:Effect of phosphorylation by cyclic AMP-dependent protein kinase on the smooth muscle actomyosin Mg2+-ATPase stimulatory activity of fodrin. 295 61

Evidence is presented for the presence of both diethylstilbestrol (DES)-sensitive and DES-insensitive Mg2+-ATPase activities in plasma membrane enriched fractions of Dictyostelium discoideum. When removed from the membrane, the DES-sensitive activity is markedly less stable than the DES-insensitive activity, and the two activities display a number of quite distinct properties. The DES-sensitive enzyme has a decided preference for Mg2+ over Ca2+, displays saturation kinetics in response to ATP as substrate (Km = 0.2 mM) and has a narrow pH optimum range. In contrast, the DES-insensitive activity is stimulated equally by Mg2+ or Ca2+, is not saturable by ATP within the mM concentration range and has a much broader pH optimum. The DES-insensitive activity has been purified extensively. The purified enzyme is inhibited by vanadate and fluoride, but is insensitive to N,N'-dicyclohexylcarbodiimide (DCCD), N-ethylmaleimide and thimerosal. In the absence of divalent cations, the enzyme displays a sigmoidal activity curve in response to substrate concentration, which is abolished by addition of either Mg2+ or Ca2+, suggesting a binding site for a divalent cation and a positive cooperative interaction. The enzyme is capable of hydrolyzing other nucleotide triphosphates and ADP, but is without activity on AMP, p-nitrophenyl phosphate and pyrophosphate. The enzyme has an apparent molecular weight of approximately 64,000.
...
PMID:Purification and characterization of a Ca2+- or Mg2+-stimulated ATPase from plasma membrane enriched fractions of Dictyostelium discoideum. 297 51

The effects of dibutyryl cyclic AMP (db-cAMP) and dibutyryl cyclic GMP (db-cGMP) were tested on Ca2+-ATPase, Mg2+-ATPase, and (Ca2+ + Mg2+)-ATPase activities in lysed synaptosomes prepared from whole rat brains (minus cerebellum). At concentrations from 0.1 to 2.0 mM, db-cGMP produced a selective, concentration-dependent increase in Ca2+-ATPase activity. Both db-cGMP and db-cAMP slightly reduced Mg2+-ATPase activity, whereas neither compound had concentration-dependent effects on (Ca2+ + Mg2+)-ATPase activity. These findings suggest that the Mg2+-independent, Ca2+-ATPase activity in rat brain is regulated by a cyclic GMP-dependent process. Further, the data provide evidence that the Ca2+-ATPase activity in lysed synaptosomal membranes represents an enzyme that is distinguishable from both the Mg2+ -and (Ca2+ + Mg2+)-ATPase.
...
PMID:Dibutyryl-cyclic GMP stimulation of Ca2+ -ATPase activity in rat brain synaptic membranes. 299 19

Intact synaptosomes isolated from the electric organ of the electric ray Torpedo marmorata contain, at their surface, enzyme activities for the hydrolysis of externally applied nucleoside phosphates. The diazonium salt of sulfanilic acid, as a low-molecular-weight, slowly permeating, covalent inhibitory agent, selectively blocks these enzyme activities and leaves intracellular lactate dehydrogenase intact. The ectoenzymes comprise both a nucleoside triphosphate and diphosphate phosphohydrolase, as well as a 5'-nucleotidase. Activity of nonspecific ectophosphatases is absent. The nucleoside triphosphatase hydrolyzes almost equally well ATP, GTP, CTP, UTP, and ITP and is activated to a similar degree by Mg2+ or Ca2+. It has a high affinity for ATP (Km for ATP in the presence of Mg2+, 75 microM; in the presence of Ca2+, 66 microM). Maximal rates in the presence of Mg2+ and Ca2+ were very similar (34.8 and 32.5 nmol of Pi/min/mg of synaptosomal protein, respectively). Either Mg-ATP or Ca-ATP can act as a true substrate. ADP inhibits hydrolysis of ATP, but AMP is without effect. The nucleoside triphosphatase is not inhibited significantly by a number of inhibitors of mitochondrial Mg2+-ATPase or of Ca2+ + Mg2+-ATPases. It is, however, considerably inhibited by filipin and quercitin. The capacity of intact synaptosomes to hydrolyze also extracellular ADP, GDP, AMP, GMP, and IMP suggests that the nucleoside triphosphatase is part of an enzyme chain that causes complete hydrolysis of the respective nucleoside triphosphate to the nucleoside. We conclude that the cholinergic nerve terminals of the Torpedo electric organ can hydrolyze ATP released on coexocytosis with acetylcholine via an ectonucleoside triphosphatase activity that is different from known endogenous nerve terminal ATPases. The final product of the hydrolysis, adenosine, can then be salvaged by the nerve terminal for resynthesis of ATP. Other possible physiological functions of the ectonucleotidases are discussed.
...
PMID:Ectonucleotidase activities associated with cholinergic synaptosomes isolated from Torpedo electric organ. 301 88

Components of the calmodulin system (i.e., calmodulin levels and activities of the following calmodulin-dependent enzymes: Ca2+ + Mg2+-ATPase, adenylate and guanylate cyclases, cyclic AMP and cyclic GMP phosphodiesterases, and Ca2+-dependent protein kinase were studied in the following brain regions from immature (25-day-old), mature (3-month-old) and aged (22-month-old) mice: striatum, cortex, cerebellum, diencephalon and medulla + pons. Both maturation and advanced aging were associated with significant changes in calmodulin content and in enzyme activities. The study provides evidence for important changes in the activity of this fundamental cell regulatory system in the brain during the processes of maturation and aging.
...
PMID:Effects of maturation and aging on calmodulin and calmodulin-regulated enzymes in various regions of mouse brain. 378 30

Normal adult albino and Sprague-Dawley rats, under intraperitoneal Nembutal anesthesia, were used to demonstrate enzymatic activity in the choroid plexus and ventricular ependyma. The brain tissues were perfused or immersed with cold 2% glutaraldehyde and 8% sucrose in 0.1 M cacodylate buffer (pH 7.2-7.4) for 30 min and washed overnight in the same buffer solution., The choroid plexus (lateral and fourth ventricles) and ventricular ependyma (lateral ventricle) were trimmed from the fixed and washed brain tissues, which were frozen and sectioned. For histo- and cyto-chemical study, the sections were immersed in the following incubation media; for Na+, K+-ATPase (ouabain-sensitive, K+-dependent, p-nitrophenylphosphatase: p-NPPase) according to the one-step method of Mayahara et al. (1978): for Mg2+- ATPase, Wachstein-Meisel's incubation medium (1957); for adenylate cyclase (AC), following Araki and Saito's lead citrate method (1979). The cytochemical findings gave the following results. In the choroid plexus, the ouabain-sensitive electron-dense reaction products of NA+, K+-ATPase (p-NPPase) were strongly positive in the microvilli and along the inner surface of microvilli, without showing any Mg2+-ATPase and AC activities, and all three enzymatic activities were positive along the basal plasmalemmas and negative along the lateral and apical (not including microvilli) plasmalemmas. In the ventricular ependyma, Na+,K+-ATPase (P-NPPase) activity was not found, and the reaction product of AC was observed on the apical plasmalemmas and those of Mg2+-ATPase along the basal plasmalemmas. These cytochemical findings are helpful in understanding the regulation of cerebrospinal fluid production through Na+, K+-ATPase (p-NPPase) and cyclic AMP (AC).
...
PMID:Cytochemical study on enzyme activity associated with cerebrospinal fluid secretion in the choroid plexus and ventricular ependyma. 611 20

The cyclic AMP-phosphodiesterase assay was used to quantitate the amount of calmodulin activity in various brain areas of male rats treated acutely or chronically for 5 days with morphine. The acute treatment with morphine decreased calmodulin activity in the mitochondrial-synaptosomal P2 fraction of the striatum, midbrain, and thalamus but had no effect on the cerebellum, which contains a low density of opiate receptors. The decrease in calmodulin activity by morphine was dose-dependent and was blocked by the opiate antagonist naloxone. In contrast, chronic treatment of rats with morphine increased calmodulin activity in the mitochondrial-synaptosomal P2 of the striatum, midbrain, cerebral cortex, and thalamus. A highly sensitive Ca2+/Mg2+-ATPase assay was also used to quantitate the amount of calmodulin activity in subcellular fractions obtained from the striatum. Chronic morphine treatment caused a significant increase in calmodulin activity in the membrane containing microsomal, synaptosomal, and mitochondrial layers but only a small change in the layer that contained the soluble proteins and the synaptic vesicles. It is suggested that alteration of the content of calmodulin in specific subcellular sites may have a central role in opiate action and addiction via regulation of multiple calmodulin-sensitive biochemical pathways.
...
PMID:Effects of acute and chronic morphine treatment of calmodulin activity of rat brain. 612 69

Various reaction intermediates of sarcoplasmic reticulum Ca2+,Mg2+-ATPase were stabilized and accumulated by modifying a specific SH group or by using nucleotide analogs. Conformational changes of the Ca2+,Mg2+-ATPase during the catalytic cycle were studied in the stabilized intermediates by the use of fluorescent and spin probes, which were introduced at specific SH groups of ATPase, namely one highly reactive but functionally nonessential (SHN) and one essential for the decomposition of the E-P intermediate (SHD) [Kawakita, M., et al. (1980) J. Biochem. 87, 609-617]. The fluorescence intensity of N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide attached to SHD decreased by 2.5% upon addition of 10 microM AMP-P(NH)P provided that Ca2+ was also present. The AMP-P(NH)P-induced fluorescence change could also be detected by using other fluorescent probes such as N-[p-(2-benzimidazolyl)phenyl]maleimide and N-(1-anilinonaphthyl-4)maleimide. Moreover, labeling at SHN gave similar results. When SHN was labeled with N-[p-(2-benzimidazolyl)phenyl]maleimide, the fluorescence intensity also decreased by 2.5% upon addition of ATP only in the presence of Ca2+, where E-P formation took place. A conformational difference between ECa1-P X ADP and ECa1-P was suggested from saturation transfer ESR measurement of spin-labeled ATPase by using ADP beta S as an ADP analog to cause accumulation of ECa1-P X ADP beta S complex. Possible structural similarities among some of the intermediates are discussed based on these findings.
...
PMID:Studies on conformational transitions of Ca2+,Mg2+-adenosine triphosphatase of sarcoplasmic reticulum. II. Conformational characteristics of stabilized reaction intermediates as revealed by fluorescent and paramagnetic probes. 613 71

Ca2+-Mg2+-ATPase of sarcoplasmic reticulum was subjected to trypic digestion under various conditions and the cleavage patterns were compared. The first tryptic cleavage to yield the NH2-terminal A-fragment (Mr approximately equal to 55,000) and COOH-terminal B-fragment (Mr approximately equal to 45,000) [Thorley-Lawson, D.A. & Green, N.M. (1977) Biochem. J. 167, 739-748] was little affected by adding ligands such as Ca2+ and AMP-P(NH)P. On the other hand, subsequent splitting of A-fragment into A1 (Mr approximately equal to 30,000) and A2 (Mr approximately equal to 20,000), and further cleavages giving rise to three smaller fragments of Mr approximately equal to 27,000-28,000 (A1a, A1b, and C) [Saito, K., et al. (1984) J. Biochem. 95, 1297] were profoundly affected by these ligands. A difference in cleavage sites was noted depending on Ca2+ ion concentration; thus, A1b and C were the major components remaining after digestion in the presence and absence of Ca2+, respectively. AMP-P(NH)P markedly stabilized both A1 and A2 fragments, but the effect was much more prominent when Ca2+ was simultaneously present on the transport site. These findings suggest that conformational changes of the ATPase molecule upon binding of Ca2+, AMP-P(NH)P, or both are accompanied by corresponding changes in the susceptibility to tryptic digestion. Fragments A1 and A2 were both quite stable and fragmentation did not proceed beyond A1, when sarcoplasmic reticulum membranes were treated with trypsin at 0 degrees C. Significant further fragmentation of A1 was observed only above 20 degrees C, suggesting a conformational transition of the ATPase protein around that temperature.
...
PMID:Conformational change of Ca2+,Mg2+-adenosine triphosphatase of sarcoplasmic reticulum upon binding of Ca2+ and adenyl-5'-yl-imidodiphosphate as detected by trypsin sensitivity analysis. 614 6


<< Previous 1 2 3 Next >>

---