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:3.1.3.1 (alkaline phosphatase)
47,916 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oxygen uptake in human placental mitochondria was stimulated by ATP addition. ATP-induced respiration was supported by malate, alpha-keto glutarate, and succinate, and inhibited by oligomycin and carboxytractyloside. This phenomenon was not caused by contamination with unspecific phosphatases or alkaline phosphatase, since NaF, L-phenyl alanine, or P1, P5-di-(adenosine-5') pentaphosphate failed to inhibit oxygen uptake induced by ATP. The stimulation of respiration was caused by an ATPase activity tightly bound to mitochondria, which yields ADP that is responsible for the oxygen uptake. The stimulation was not an uncoupling effect because ATP addition produced a transition between state 3 and 4 of respiration, indicating that ATP was not released from mitochondria.
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PMID:Respiratory control induced by ATP in human term placental mitochondria. 836 13

Preincubation of rat hepatocytes with isoproterenol induces homologous beta-adrenergic desensitization evidenced both in whole cells (cyclic AMP accumulation) and membranes (adenylyl cyclase activity). This desensitization is associated with and quantitatively similar to a loss of beta 2-adrenoceptors from the plasma membrane. Desensitization did not alter the affinities of isoproterenol for the [125I]iodocyanopindolol binding sites nor reduce the ability of guanine nucleotides to modulate agonist affinity, i.e., the receptors that remain in the surface of plasma membrane after desensitization (approximately 50%) retain their functional integrity. When membranes from isoproterenol-desensitized hepatocytes were treated with alkaline phosphatase, no attenuation of the desensitization was observed. Cholera toxin-catalyzed ADP-ribosylation was not decreased but rather slightly increased in membranes from desensitized cells as compared to the controls. Our data indicate that in hepatocytes, a loss of beta 2-adrenoceptors from the plasma membrane is closely associated to the homologous desensitization induced by isoproterenol.
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PMID:Hepatocyte homologous beta 2-adrenergic desensitization is associated with a decrease in number of plasma membrane beta 2-adrenoceptors. 838 42

Using AMP deaminase (AMP aminohydrolase; EC 3.5.4.6) purified from rabbit left-ventricular heart tissue, we report direct investigation of the potential for cardiac AMP deaminase activity to be regulated by kinase-mediated phosphorylation. Rabbit heart AMP deaminase served as a substrate for Ca2+/phospholipid-dependent protein kinase (protein kinase C; PKC) exclusively; no other mammalian protein kinase phosphorylated the enzyme. PKC-dependent AMP deaminase phosphorylation was rapid, linear with respect to time and the concentrations of PKC and AMP deaminase in the reaction, and inhibitable by staurosporine. Upon phosphorylation, the apparent Km of cardiac AMP deaminase decreased from 5.6 mM to 1.2 mM, without effect on the Vmax. Whether phosphorylated or not, rabbit heart AMP deaminase was inhibited by 1.0 mM GTP, which decreased the Vmax. by approximately 50% in each case. PKC-dependent phosphorylation of cardiac AMP deaminase did not alter the enzyme's allosterism toward millimolar ATP or ADP: both nucleotides at 1.0 mM concentration decreased the apparent Km to approximately 0.5 mM. Treatment of cardiac phospho-AMP deaminase with either the protein phosphatase calcineurin or alkaline phosphatase generated a dephosphorylated form which displayed molecular and kinetic properties identical with those of the originally isolated enzyme. These data raise the possibility that a phosphorylation-dephosphorylation mechanism may regulate flux through AMP deaminase in the heart under pathological conditions, such as myocardial ischaemia, characterized by PKC activation and adenylate depletion.
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PMID:Modulation of mammalian cardiac AMP deaminase by protein kinase C-mediated phosphorylation. 838 71

Exogenous adenosine triphosphate (ATP) added to brush-border membrane vesicles was rapidly degraded mainly to inosine according to the high ecto-nucleotidase activities in these vesicles. In the absence of phosphate, inosine was slowly transformed into hypoxanthine, and xanthine oxidase and dehydrogenase activities were not detected. The presence of ecto-adenosine deaminase and ecto-adenosine monophosphate (AMP) nucleotidase was shown. The ecto-adenosine deaminase was inhibited by deoxycoformycin and was also detected in rat renal brush-border membrane vesicles. Using orthovanadate, levamisole, and alpha, beta-methylene adenosine diphosphate as possible inhibitors, alkaline phosphatase was shown to be the main agent responsible for ecto-AMP nucleotidase activity. In pig renal basolateral membrane vesicles and in whole cell extracts from pig renal cortex, ecto-AMP nucleotidase was the limiting factor in ATP degradation. Comparing the ATP catabolism in the whole cell cortical extract with the catabolism in the same sample precleared of membranes, it was shown that ectonucleotidase activity is mainly bound to the membranous components. It is also shown that the whole cell extract of pig renal cortex has hypoxanthine phosphoribosyl transferase activity, and it seems probable that the rapid and specific formation of luminal inosine and its transport into the cell in competition with adenosine may start the purine salvage pathway through the synthesis of IMP from hypoxanthine.
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PMID:Adenine nucleotides and adenosine metabolism in pig kidney proximal tubule membranes. 840 44

A novel type of ATP-diphosphohydrolase (ATPDase) is demonstrated in bovine lung. The enzyme has an optimum pH of 7.5 and catalyzes the hydrolysis of the beta- and gamma-phosphate residues from diphospho- and triphosphonucleosides. It requires Ca2+ or Mg2+ and is insensitive to ouabain, an inhibitor of Na+/K(+)-ATPase, P1,P5-di(adenosine 5')-pentaphosphate, an inhibitor of adenylate kinase, and tetramisole, an inhibitor of alkaline phosphatase. In contrast, sodium azide (10 mM), a known inhibitor of ATPDases and mitochondrial ATPases, as well as mercuric chloride (10 microM) and gossypol (2,2'-bis[8-formyl-1,6,7-trihydroxy-5-isopropyl-3-methylnaphthalene]) (35 microM) are powerful inhibitors of this enzyme. The same inhibition profile is obtained with ATP or ADP as substrate, thereby supporting the concept of a common catalytic site for these substrates. This is further confirmed by enzyme localization after polyacrylamide gel electrophoresis under nondenaturing conditions and by kinetic properties, namely pH dependence profiles, heat inactivation, and 60Co irradiation-inactivation curves. The native molecular mass of the enzyme calculated from 60Co gamma-irradiation-inactivation curves is estimated at 70 +/- 3 kDa, whereas Km,app and Vmax,app of the ATPDase are evaluated at 7 +/- 2 microM and 1.1 +/- 0.3 mumol of Pi/min/mg protein, respectively. A comparison of the kinetic properties of this ATPDase with those of pig pancreas (Type I) and bovine aorta (Type II) lead us to believe that this enzyme is an hitherto undescribed type of ATPDase. By reference to the previously described ATPDase, we propose to identify this enzyme as ATPDase Type III (EC 3.6.1.5).
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PMID:Demonstration of a novel type of ATP-diphosphohydrolase (EC 3.6.1.5) in the bovine lung. 844 44

ATP diphosphohydrolase activity (ATP-DPH) has been previously identified in the particulate fraction of human term placenta [Papamarcaki, T. & Tsolas, O. (1990) Mol. Cell. Biochem. 97, 1-8]. In the present study we have purified to homogeneity and characterized this activity. A 260-fold purification has been obtained by solubilization of the particulate fraction and subsequent chromatography on DEAE Sepharose CL-6B and 5'-AMP Sepharose 4B. The preparation has been shown to be free of alkaline phosphatase even though the placental extract is rich in this activity. The purified enzyme is a glycoprotein and migrates as a single broad band of 82 kDa on SDS/PAGE. The same band is obtained after photoaffinity labeling of the enzyme with 8-azido-[alpha-32P]ATP. The enzyme has a broad substrate specificity, hydrolyzing triphosphonucleosides and diphosphonucleosides but not monophosphonucleosides or other phosphate esters. The activity is dependent on the addition of divalent cations Ca2+ or Mg2+. The Km values for ATP and ADP were determined to be 10 microM and 20 microM, respectively. Maximum activity was found at pH 7.0-7.5 with ATP as substrate, and pH 7.5-8.0 with ADP. The enzymic activity is inhibited by NaN3, NaF, adenosine 5'-[beta,gamma-imido]triphosphate and adenosine 5'-[alpha,beta-methylene]triphosphate. Protein sequence analysis showed ATP-DPH to be N-terminally blocked. Partial internal amino acid sequence information was obtained after chymotryptic cleavage and identified a unique sequence with no significant similarity to known proteins. ATP-DPH activity has been reported to be implicated in the prevention of platelet aggregation, hydrolysing ADP to AMP and thus preventing blood clotting.
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PMID:Purification and properties of human placental ATP diphosphohydrolase. 852 70

1. Single channel current recordings were used to study the characteristics of a large conductance Ca(2+)-activated K+ (BKCa) channel present in neurones acutely dissociated from the rat motor cortex. Application of ATP to the intracellular surface of excised inside-out patches produced a large, concentration-dependent increase in BKCa channel activity. 2. This ATP-mediated activation was dependent upon the presence of Mg2+ in the intracellular bathing solution and was diminished by the phosphatases 2,3-butanedione monoxime (BDM) or alkaline phosphatase and by the protein kinase inhibitors staurosporine, H-7 and PKI. 3. ADP stimulated BKCa channel activity in a Mg(2+)-dependent manner, an action also inhibited by the concomitant application of PKI or BDM. The effect of ADP was reduced by application of hexokinase and glucose or by application of the adenylate kinase inhibitor Ap5A. 4. Of other nucleotides tested, only CTP consistently activated BKCa channel activity. 5. Using the cell-attached configuration, bath application of forskolin or dibutyryl cAMP stimulated BKCa channel activity. 6. It is concluded that BKCa channel activity in the rat motor cortex is subject to modulation by the activity of a closely associated kinase. The ability of cAMP activators to stimulate BKCa channel activity in the intact cell suggests that this system may be of physiological importance.
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PMID:Characterization of an ATP-modulated large conductance Ca(2+)-activated K+ channel present in rat cortical neurones. 856 73

The substrate specificity of the cyanobacterial dual-specificity protein phosphatase, IphP, was explored using a variety of potential substrates. The enzyme displayed phosphomonoesterase activity toward a broad range of peptide, protein, and low molecular weight organophosphate compounds. It displayed little or no hydrolase activity toward phosphodiesters, phosphoramides, carboxyl esters, or sulfoesters. However, it did display measurable pyrophosphatase activity, especially toward ADP and ATP. Among the low molecular weight phosphomonoesters, the presence of an aromatic ring either as part of the leaving group alcohol or immediately adjacent thereto, as in 5'-AMP, was a strong positive determinant for hydrolysis. Among peptide and protein substrates, a rough, but imperfect, correlation between charge character and hydrolysis was noted in which proteins and phosphorylation sites of an acidic nature seemed favored. Heparin affected IphP activity in a substrate-dependent manner. Toward small organophosphates, heparin had no significant effect, but it was inhibitory toward most protein and peptide substrates. However, toward phosphoseryl casein and MAP kinase, it enhanced activity as much as 10-fold. This enhancement was attributed to the ability of heparin to bind to these substrate proteins, as well as IphP, and recruit them to the same microenvironment.
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PMID:Substrate specificity of IphP, a cyanobacterial dual-specificity protein phosphatase with MAP kinase phosphatase activity. 865 37

1. Using the incorporation of [methyl-3H]thymidine as a proliferation marker, the effects of various nucleosides and nucleotides on endothelial LLC-MK2 cells were studied. We found that ATP, ADP, AMP and adenosine in concentrations of 10 microM or higher stimulate the proliferation of these cells. 2. Inhibition of ecto-ATPase (EC 3.6.1.15), 5'-nucleotidase (EC 3.1.3.5) or alkaline phosphatase (EC 3.1.3.1) significantly diminished the stimulatory effect of ATP, indicating that the effect is primarily caused by adenosine and not by adenine nucleotides. Also, the effect depends only on extracellular nucleosides, since inhibition of nucleoside uptake by dipyridamole has no influence on proliferation. 3. Other purine nucleotides and nucleosides (ITP, GTP, inosine and guanosine) also stimulate cell proliferation, while pyrimidine nucleotides and nucleosides (CTP, UTP, cytidine and uridine) inhibit proliferation. Furthermore, the simultaneous presence of adenosine and any of the other purine nucleosides is not entirely additive in its effect on cell proliferation. At the same time any pyrimidine nucleoside, when added together with adenosine, has the same inhibitory effect as the pyrimidine nucleoside alone. 4. Apparently these proliferative effects are neither caused by any pharmacologically known P1-purinoceptor, nor are they mediated by cyclic AMP, cyclic GMP, or D-myo-inositol 1,4,5-trisphosphate as second messenger, nor by extracellular Ca2+. 5. Therefore, we conclude that various purine and pyrimidine nucleosides can influence the proliferation of LLC-MK2 cells by acting on putative purinergic and pyrimidinergic receptors not previously described.
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PMID:Regulation of proliferation of LLC-MK2 cells by nucleosides and nucleotides: the role of ecto-enzymes. 868

Purified chloroplast ATP synthase (CF1) contains 1.2-2 mol of tightly bound ADP/mol of enzyme that resists removal by gel filtration or dialysis. CF1 was depleted of its endogenous nucleotide by treatment with alkaline phosphatase. Tightly bound nucleotide was demonstrated not to have an essential structural role. CF1 depleted of endogenous nucleotide retains its ability to catalyze Ca2+- and Mg2+-dependent ATPase activity and is not more sensitive to cold inactivation than untreated CF1. 2'(3')-O-Trinitrophenyladenosine 5'-diphosphate (TNP-ADP) binds tightly to two sites on nucleotide-depleted CF1, binding to either site at a faster rate than that of exchange of bound nucleotide for medium nucleotide. The nucleotide-depleted enzyme binds about one additional mol of TNP-ADP/mol of CF1, indicating that there is a tight TNP-ADP binding site that does not exchange readily with medium nucleotide. It is MgADP in this nonexchanging site, not the easily exchanging ADP binding site, that is responsible for the MgADP-induced inhibition of the ATPase activity. The rate of exchange of tightly bound ADP from CF1 matches the rate at which the Mg2+ATPase activity of CF1 is activated but is not itself responsible for the activation.
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PMID:Differences between two tight ADP binding sites of the chloroplast coupling factor 1 and their effects on ATPase activity. 870 14


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