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:3.6.1.25 (triphosphatase)
1,529 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adenosine triphosphatase activity which is Mg2+-dependent and stimulated by submicromolar concentrations of Ca2+ (as Ca . ATP) was identified in the total particulate fraction of rat pancreatic acini. Half-maximal activity (V0.5) is obtained at 100.1 +/- 6 nM Ca . ATP with a Hill coefficient of 2.2 +/- 0.1 (mean +/- S.E.; n = 4). Maximal activity was 75 +/- 19 pmol of Pi released from ATP minute-1 microgram of membrane protein-1 (mean +/- S.E.; n = 7). High affinity Ca2+-ATPase activity was unaffected by ouabain, Na+, K+, La3+, and added calmodulin. Activity was slightly reduced by ruthenium red (0.1 mM) and by oligomycin (80 micrograms/ml) but was reduced almost 50% by the phenothiazine derivative fluphenazine in a dose-related and Ca2+-dependent manner. Hydrolysis of p-nitrophenyl phosphate was 9% of the rate of ATP hydrolysis and was independent of Ca2+ concentration. However, ADP, GTP, UTP, and ITP were hydrolyzed at 76-93% the rate that ATP was hydrolyzed with V0.5 values and Hill coefficients similar to those of Ca . ATP. We conclude that rat pancreatic acini contain an enzyme for active Ca2+ translocation: ATPase activity that is Mg2+-dependent and stimulated by submicromolar concentrations of Ca . ATP. Substrate hydrolysis appears to involve positive cooperative interactions of multiple ligand-binding sites and may be regulated in part by calmodulin.
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PMID:High affinity, calcium-stimulated adenosine triphosphatase activity in the particulate fraction of rat pancreatic acini. 623 78

The contractile system of smooth muscle exhibits distinctive responses to varying Mg2+ concentrations in that maximum adenosine-5'-triphosphatase (ATPase) activity of actomyosin requires relatively high concentrations of Mg2+ and also that tension in skinned smooth muscle fibers can be induced in the absence of Ca2+ by high Mg2+ concentrations. We have examined the effects of MgCl2 on actomyosin ATPase activity and on tension development in skinned gizzard fibers and suggest that the MgCl2-induced changes may be correlated to shifts in myosin conformation. At low concentrations of free Mg2+ (less than or equal to 1 mM) the actin-activated ATPase activity of phosphorylated turkey gizzard myosin is reduced and is increased as the Mg2+ concentration is raised. The increase in Mg2+ (over a range of 1-10 mM added MgCl2) induces the conversion of 10S phosphorylated myosin to the 6S form, and it was found that the proportion of myosin as 10S is inversely related to the level of actin-activated ATPase activity. Activation of the actin-activated ATPase activity also occurs with dephosphorylated myosin but at higher MgCl2 concentrations, between 10 and 40 mM added MgCl2. Viscosity and fluorescence measurements indicate that increasing Mg2+ levels over this concentration range favor the formation of the 6S conformation of dephosphorylated myosin, and it is proposed that the 10S to 6S transition is a prerequisite for the observed activation of ATPase activity. With glycerinated chicken gizzard fibers high MgCl2 concentrations (6-20 mM) promote tension in the absence of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of magnesium chloride on smooth muscle actomyosin adenosine-5'-triphosphatase activity, myosin conformation, and tension development in glycerinated smooth muscle fibers. 623 28

1. Pig aortic endothelial and smooth-muscle cells in culture rapidly catabolize exogenous ATP, ADP or AMP. 2. In both cell types catabolism is due to Mg2+-stimulated ectoenzymes. 3. Inhibition and substrate-specificity studies suggest that both cell types possess three distinct ectonucleotidases, namely nucleoside triphosphatase (EC 3.6.1.15), nucleoside diphosphatase (EC 3.6.1.6) and 5'-nucleotidase (EC 3.1.3.5), as well as nucleoside diphosphate kinase (EC 2.7.4.6). 4. These ectonucleotidase systems could be of importance in the regulation of neurotransmission, blood platelet function and vasodilation.
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PMID:Metabolism of adenine nucleotides by ectoenzymes of vascular endothelial and smooth-muscle cells in culture. 625 67

Three distinct enzymes hydrolyzing either ApppA or AppppA, or both, were separated and purified from yellow lupin seed extracts. Two of the enzymes were purified to homogeneity. These enzymes differ greatly in their catalytic and physical properties. One hydrolase, with a native molecular weight of 41,000, exhibits broad pH (from 5-8) optimum for activity, requires Mg2+ for activity, is inhibited by zinc ions (I0.5 = 25 microM) and hydrolyses ApppA (V = 1), ApppC (V = 0.38), ApppG (V = 0.2), and ribose(5')pppA (V = 0.2). The enzyme exhibits much lower activity with AppppA (V = 0.1), and ApppppA, AppppppA, ppppA, and ATP are hydrolyzed 25- to 100-fold slower then ApppA. ADP was always one of the products of the reactions catalyzed by the enzyme. AppA, NAD, NADP, FAD, cAMP, and p-nitrophenyl-thymidine 5'-phosphate were not hydrolyzed by the enzyme. The enzyme is diadenosine 5',5"'-P1, P3-triphosphatase. The second hydrolase, composed of one polypeptide chain of a molecular weight 18,000-18,500, exhibits optimal activity in the pH range from 7.5-9, requires Mg2+ for activity, is inhibited by calcium ions (I0.5 for calcium depends on the concentration of Mg2+ and is 35-180 microM in the presence of 0.5-10 mM Mg2+, respectively), and hydrolyzes AppppA (V = 1, Km = 1 microM), ApppppA (V = 0.42, Km = 1.8 microM), AppppppA (V = 0.34), AppppU (V = 0.73), AppppC (V = 0.67), AppppG (V = 0.27), and ppppA. ATP was always one of the products of the reactions catalyzed by the enzyme. Dinucleoside di- and triphosphates, ATP, cAMP, and p-nitrophenylthymidine 5'-phosphate were not hydrolyzed by the enzyme. This enzyme is diadenosine 5',5"'-P1,P4-tetraphosphatase (EC 3.6.1.17). The third hydrolase, composed of one polypeptide chain of a molecular weight of 56,000, exhibits maximal activity at pH 9-10.5, does not require Mg2+ ions for activity, is inhibited neither by divalent cations (Mg2+, Ca2+, Zn2+, Co2+, Mn2+, or Ni2+) nor by EDTA, and uses as substrates all compounds which are substrates for the diadenosine 5',5"'-P1,P3-triphosphatase and diadenosine 5',5"'-P1,P4-tetraphosphatase. In addition, the enzyme hydrolyzes p-nitrophenyl-thymidine 5'-phosphate, p-nitrophenylthymidine 3'-phosphate, bis-p-nitrophenylphosphate, ADP, AppA, NAD, NADP, and FAD, but not cAMP. With the exception of p-nitrophenylphosphate derivatives all other substrates of the enzyme yield AMP as one of the products of hydrolysis. This enzyme has a specificity similar to that of phosphodiesterases (EC 3.1.4.1) from other sources. With the lupin phosphodiesterase, ApppA (V = 1, Km = 2.2 microM) and AppppA (V = 1, Km = 2.0 microM) are better substrates than NAD (V = 0.8, Km = 9.6 microM), AppA (V = 0.4), ApppppA (V = 0.6), and AppppppA (V = 0.34).
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PMID:Enzymes hydrolyzing ApppA and/or AppppA in higher plants. Purification and some properties of diadenosine triphosphatase, diadenosine tetraphosphatase, and phosphodiesterase from yellow lupin (Lupinus luteus) seeds. 630 93

Magnesium ions are important for maintaining the functional and structural integrity of the myocardium. Epidemiologic studies suggest that myocardial hypomagnecytia can predispose to sudden cardiac death and that hard water protective factor preventing heart attack could be magnesium. Recent studies show that infarcted portion of the myocardium has lowered magnesium content as compared to noninfarcted segment. Magnesium deficiency sensitises the myocardium to the toxic effect of various drugs, hypoxia etc. and magnesium administration is protective. The metabolic, biochemical and electrophysiologic effects of magnesium appear to be significant in treatment of myocardial ischaemia. Magnesium is a metal-coenzyme and activates adenosine-triphosphatase which may be inhibited by nonglucose fuels like lactate and free fatty acids. Magnesium deficiency may be responsible for the chronic electrical instability of the myocardium predisposing to sudden cardiac death. The acute precipitating stress dependent trigger which lie in the brain may also be related to magnesium. In addition to fast Na and Ca channels there could be a Mg-carrying transport system maintaining the electrical activity of the myocardium. There is sufficient evidence to suggest the use of magnesium salts against ischaemic heart disease and sudden cardiac death. Magnesium is cardioprotective and influences action potential duration, membrane potential and perhaps maintains the fast response. The therapeutic and prophylactic value of magnesium needs further assessment.
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PMID:Magnesium in atherosclerotic cardiovascular disease and sudden death. 697 57

GTP:mRNA guanylyltransferase, an enzyme that catalyzes the transfer of a GMP residue from GTP to the 5' end of RNA to form a cap structure identified as G(5')pppN-, has been isolated from HeLa cell nuclei. The enzyme has been purified approximately 1000-fold and separated by column chromatography (using DEAE-cellulose, phosphocellulose, Cibacron blue-agarose, and GTP-agarose) from a variety of other activities, including RNA triphosphatase and mRNA (guanine-7)methyltransferase. The reaction product was identified by its resistance to Penicillium nuclease and alkaline phosphatase, sensitivity to venom phosphodiesterase, and electrophoretic and chromatographic mobilities relative to authentic standards. Optimal enzyme activity was obtained at pH 7.5 in the presence of Mn2+ or Mg2+, GTP, and an appropriate acceptor polyribonucleotide. The enzyme was inhibited by elevated concentrations of salt and by sulfhydryl-binding reagents but was unaffected by S-adenosylmethionine or S-adenosylhomocysteine. A molecular weight of 48,500 was estimated by sucrose gradient centrifugation of purified enzyme.
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PMID:Purification and characterization of mRNA guanylyltransferase from HeLa cell nuclei. 735 12

This article presents a fluorimetric study of the main properties of the enzymes dinucleoside tetraphosphate (asymmetrical) hydrolase or dinucleoside tetraphosphatase (Ap4Aase, EC 3.6.1.17) and dinucleoside triphosphate hydrolase or dinucleoside triphosphatase (Ap3Aase, EC 3.6.1.29), both present in adrenal medulla cytosolic extracts. Diethenoadenosine polyphosphates, epsilon-(ApnA), are used as artificial fluorogenic substrates. Ap4Aase exhibits a molecular mass around 20 kDa and neutral optimum pH (7.0-7.5). It requires Mg2+ and preferentially hydrolyzes substrates with four phosphate groups. Km for epsilon-(Ap4A) is 1.3 microM and Ki for Ap4A and Gp4G are 1 and 0.2 microM respectively. Km for Ap4A determined by HPLC is 1.6 microM. epsilon-(Ap5A) and epsilon-(Ap6A) are hydrolyzed at reduced rates. This enzyme is inhibited by Zn2+, F- and very strongly by Ap4 and epsilon-Ap4. Ca2+ cannot replace Mg2+, but behaves as inhibitor in its presence. The substrate analogs dinucleoside triphosphates Ap3A, G;3G, m7Gp3G and m7Gp3A and the periodate-oxidized nucleotides o-(Ap4A), o epsilon-(Ap4A), o-Ap4 and o epsilon-Ap4 behave as inhibitors. Ap3Aase exhibits a molecular mass around 30 kDa and neutral optimum pH (7.0-7.5). It requires Mg2+ or Ca2+, but retains a low measurable activity around 10% in the absence of these divalent cations. It only hydrolyzes substrates with three phosphate groups. Km for epsilon-(Ap3A) is 11 microM and Ki for Ap3A and Gp3G are 20 and 22 microM, respectively. Km for Ap3A determined by HPLC is 16 microM. m7Gp3G and m7Gp3A are also good substrates for triphosphatase.
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PMID:Specific dinucleoside polyphosphate cleaving enzymes from chromaffin cells: a fluorimetric study. 749 90

The Hepatitis C Virus (HCV) NS3 protein contains amino acid motifs of a serine proteinase, a nucleotide triphosphatase (NTPase), and an RNA helicase based on amino acid sequence analysis. Proteinase and NTPase activities of the HCV NS3 protein were reported by several investigators. Here, we show that the recombinant HCV NS3 protein purified from a T7 promoter and His-tag expression system possesses an RNA helicase activity. The recombinant HCV NS3 protein consists of 466 amino acids from the carboxy terminal of a HCV NS3 open reading frame and 25 additional residues from the vector. The recombinant HCV NS3 protein was purified by metal-binding chromatography. The helicase activity requires ATP and divalent cations such as Mg2+ and Mn2+. The helicase activity was abolished by monoclonal antibody specific to the HCV NS3 protein.
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PMID:C-terminal domain of the hepatitis C virus NS3 protein contains an RNA helicase activity. 757 85

To directly assess the possible role of ADP in muscle fatigue, we have studied the effect of physiological MgADP levels on maximum Ca(2+)-activated isometric force and unloaded shortening velocity (Vus) of single skinned fiber segments from rabbit fast-twitch (psoas) and slow-twitch (soleus) muscles. MgADP concentration was changed in a controlled and well-buffered manner by varying creatine (Cr) in solutions, which also contained MgATP, phosphocreatine (PCr), and creatine kinase (CK). To quantify ADP as a function of Cr added, we determined the apparent equilibrium constant (K') of CK for the conditions of our experiments (pH 7.1, 3 mM Mg2+, 12 degrees C): K' = (sigma [Cr]. sigma [ATP])/(sigma [PCr]. sigma [ADP]) = 260 +/- 3 (SE). In this manner, ADP was altered essentially as occurs during stimulation in vivo but without the concomitant changes in pH and P(i), which affect force and Vus. As ADP (and Cr) was increased, force and Vus decreased in both fiber types; at the highest ADP level used, 200 microM, normalized force was 96.6 +/- 1.7% for psoas (n = 6) and 93.7 +/- 2.8% for soleus (n = 6), and Vus was 80.4 +/- 2.4% for psoas and 91.3 +/- 7.7% for soleus. Diffusion-reaction calculations indicated that radial gradients of metabolite concentrations within fibers could not explain the small effects of ADP on fiber mechanics, and experiments verified that metabolite levels were well buffered within fibers by the CK reaction. Exogenous CK was added to bathing solutions at 290 U/ml, threefold above that necessary to maintain Vus independent of CK concentration; in the absence of PCr and exogenous CK, at least a fourfold increased MgATP was necessary to maintain Vus at the control level. Adenylate kinase activity was not detectable; thus myofibrillar adenosine-triphosphatase and exogenous CK activities were the major determinants of nucleotide levels within activated cells. Cr alone (in absence of PCr and exogenous CK) also decreased force and Vus, presumably by a nonspecific mechanism. Over the physiological range, altered ADP had little or no effect on force or Vus in well-buffered conditions. It is therefore likely that other factors decrease force and Vus during muscular fatigue.
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PMID:Effect of physiological ADP concentrations on contraction of single skinned fibers from rabbit fast and slow muscles. 786 87

TrwC is an essential protein in conjugative DNA transfer of the broad-host-range plasmid R388. TrwC was purified in two chromatographic steps from TrwC-overproducing bacteria. The purification procedure resulted in > 90% pure TrwC protein, which was free of contaminating nuclease activities. TrwC behaved as a dimer in gel-filtration chromatography in the presence of 550 mM NaCl, and had a pI of 10.1. The purified protein showed in-vitro ssDNA-dependent nucleoside-5'-triphosphatase and DNA helicase activities. ATP was the preferred substrate for the NTP hydrolysis reaction, which required Mg2+. The helicase activity was dependent on ATP and Mg2+. The efficiency of the unwinding reaction catalyzed by TrwC ranged from > 90% of fragment displaced for a 93-nucleotide sequence to < 5% for a 365-nucleotide sequence. Unwinding was unidirectional in the 5' to 3' direction. The enzyme turned over very slowly from one DNA substrate molecule to another. TrwC is only the second DNA helicase to be described which is involved in conjugative DNA transfer. The biochemical properties of TrwC described here confirm its functional relatedness to helicase I (TraI) encoded by plasmid F of E. coli.
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PMID:Purification and biochemical characterization of TrwC, the helicase involved in plasmid R388 conjugal DNA transfer. 800 58


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