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)

Determination of the adenine and guanine nucleotides in Triton X-100-extracted cytoskeletal fractions was utilized to estimate the actin and tubulin content of the assembled cytoskeletons in nonmuscle cells. Results with stable cell lines (i.e., rat pheochromocytoma PC12 and neuroblastoma NB41A3) and with primary cultures (i.e., human foreskin fibroblasts and chick embryonic dorsal root ganglion neurons) exhibited levels of cytoskeletal fraction ADP and GDP consistent with their assembly-induced nucleoside-5'-triphosphatase activities only previously analyzed in vitro. Likewise, estimates of actin and tubulin content fall in the range of values obtained by other experimental approaches. In contrast, analysis of whole cell nucleotides showed high [ATP]/[ADP] and [GTP]/[GDP] ratios, suggesting there is little, if any, contamination of the cytoskeletal nucleotide pool by other cellular nucleotides.
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PMID:Adenine and guanine nucleotide content of Triton-extracted cytoskeletal fractions of nonmuscle cells. 151 95

Recent studies have reported abnormal platelet morphology and function in patients with adolescent idiopathic scoliosis. These abnormalities include increased platelet size and dense body numbers, abnormal aggregation, thromboxane A2 synthesis, serotonin release to adenosine diphosphate and epinephrine stimulus, and decreased myosin-adenosine-triphosphatase-specific activity. It was postulated that a membrane-specific defect in calcium transport may be partially responsible for the abnormalities found. In response to a suggestion in the literature that platelet screening could be clinically useful in scoliosis evaluation as well as in basic research of its pathophysiology, a study was performed to evaluate platelet morphology, biochemistry, and function in patients with adolescent idiopathic scoliosis. Platelets from nine volunteers with adolescent idiopathic scoliosis were compared with cells from a control group of nine patients. No significant differences in measured platelet parameters were noted between adolescent idiopathic scoliosis patients and control groups. Platelets from both groups demonstrated normal aggregation and release patterns with all agents except for a mild decreased aggregation and secretion response to epinephrine. No significant differences were noted in serotonin or adenine nucleotide levels. No significant ultrastructural differences were noted. Earlier findings of an abnormal aggregation and secretion response to adenosine diphosphate, increased numbers of dense bodies, or increased intracellular calcium could not be confirmed. On the contrary, we found normal, if not slightly decreased, numbers of dense bodies per platelet and calcium levels that were not different from controls.
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PMID:Platelet function in adolescent idiopathic scoliosis. 155 84

An enzyme able to cleave dinucleoside triphosphates has been purified 3,750-fold from Saccharomyces cerevisiae. Contrary to the enzymes previously shown to catabolize Ap4A in yeast, this enzyme is a hydrolase rather than a phosphorylase. The dinucleoside triphosphatase molecular ratio estimated by gel filtration is 55,000. Dinucleoside triphosphatase activity is strongly stimulated by the presence of divalent cations. Mn2+ displays the strongest stimulating effect, followed by Mg2+, Co2+, Cd2+, and Ca2+. The Km value for Ap3A is 5.4 microM (50 mM Tris-HCl [pH 7.8], 5 mM MgCl2, and 0.1 mM EDTA; 37 degrees C). Dinucleoside polyphosphates are substrates of this enzyme, provided that they contain more than two phosphates and that at least one of the two bases is a purine (Ap3A, Ap3G, Ap3C, Gp3G, Gp3C, m7Gp3A, m7Gp3G, Ap4A, Ap4G, Ap4C, Ap4U, Gp4G, and Ap5A are substrates; AMP, ADP, ATP, Ap2A, and Cp4U are not). Among the products, a nucleoside monophosphate is always formed. The specificity of cleavage of methylated dinucleoside triphosphates and the molecular weight of dinucleoside triphosphatase indicate that this enzyme is different from the mRNA decapping enzyme previously characterized (A. Stevens, Mol. Cell. Biol. 8:2005-2010, 1988).
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PMID:Isolation and characterization of a dinucleoside triphosphatase from Saccharomyces cerevisiae. 165 9

Evidence is presented for the existence of ectoenzymes in rat renal cortical brush-border membrane vesicles that produce adenosine as a final product using either ATP, ADP or AMP as substrate. The enzymes are insensitive to levamisole, ouabain, oligomycin and N-ethylmaleimide, and have absolute requirement for divalent cations with following order of activation Mg2+ greater than Ca2+ greater than Mn2+ greater than Ba2+ greater than Zn2+. At least two separate enzymes can be distinguished. One is capable of hydrolyzing ATP, other nucleoside triphosphates and ADP, but not AMP. The enzyme is insensitive to concanavalin A. The other enzyme hydrolyzes AMP and is strongly inhibited by this lectin. Mg2(+)-stimulated ATP hydrolysis displays saturation kinetics which is not of the simple Michaelis-Menten type, but is biphasic with a high-affinity (K'm = 0.16 mM) and low-affinity site (K'm = 9.0 mM), respectively. The low-affinity site hydrolyzes ATP, ITP and GTP to a similar extent, whereas CTP and UTP with about 40% lower rate. The high-affinity site splits ATP much better than other nucleoside triphosphates. Hydrolysis of ADP follows simple Michaelis-Menten saturation kinetic with apparent Km = 0.38 +/- 0.06 mM. Inhibition, activation and substrate specificity studies indicate that nucleoside triphosphatase and nucleoside diphosphatase may reside on the same protein. Kinetics of the AMP hydrolysis is hyperbolic with apparent Km = 76 +/- 9 microM. The cascade of ectonucleotidases in the brush-border membrane of the proximal tubule may catalyze the degradation of filtered nucleotides into adenosine and phosphate, the compounds which are thereafter probably reabsorbed by separate transport systems.
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PMID:The stepwise hydrolysis of adenine nucleotides by ectoenzymes of rat renal brush-border membranes. 217

Limited tryptic digestion of Escherichia coli transcription termination factor rho [an RNA-dependent nucleoside triphosphatase (NTPase)] yields predominantly two fragments (f1 and f2) when the protein is bound to both poly(C) and ATP. The apparent molecular masses of the two fragments are 31 kDa for f1 and 15 kDa for f2, adding up to the molecular mass of the intact rho polypeptide chain (46 kDa). Sequence analysis of the amino termini demonstrates that f1 is derived from the amino-terminal portion of rho and that the trypsin cleavage that defines f2 occurs at lysine-283. These results suggest that, in the liganded (activated) form, the native rho protein monomer is organized into two distinct structural domains that are separable by a single proteolytic cleavage. The f1 fragment, purified from NaDodSO4/polyacrylamide gels and renatured, binds poly(C) but the f2 fragment does not; neither regains any ATPase activity. ATP- and polynucleotide-dependent changes in the rate of proteolysis and in the character of the fragments produced suggest that rho undergoes a series of conformational transitions as a consequence of RNA binding, NTP binding and NTP hydrolysis. The rate of loss of rho ATPase activity and of intact rho monomers is slower in the presence of adenosine 5'-[gamma-thio]triphosphate than in the presence of either ATP or ADP, indicating that the hydrolysis of ATP may result in different conformational effects than does the binding of this ligand. These findings are discussed within the context of recent models of rho-dependent transcription termination.
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PMID:Escherichia coli transcription termination factor rho has a two-domain structure in its activated form. 258 Mar 3

The role of the endothelium in response to aggregating platelets was examined in porcine coronary and peripheral (carotid, femoral and renal) arteries from normal and hypercholesterolemic pigs. Male Yorkshire pigs were fed either a normal diet or a 2% high cholesterol diet for 10 weeks. Endothelium-dependent responses were examined in vitro. In all arteries from control animals, aggregating platelets caused endothelium-dependent relaxations, which were augmented by ketanserin (a 5-HT2-serotonergic blocker), attenuated by apyrase (an adenosine diphosphatase and triphosphatase) or methiothepin (a combined 5-HT1 and 5-HT2-serotonergic blocker) and were almost abolished by a combination of apyrase and methiothepin. The platelet-induced relaxations were most pronounced in the coronary arteries. Adenosine diphosphate caused endothelium-dependent relaxations, which were significantly attenuated by apyrase. Serotonin also caused endothelium-dependent relaxations, which were significantly attenuated by methiothepin but augmented by ketanserin. The endothelium-dependent relaxations to adenosine diphosphate were most pronounced in coronary arteries and those to serotonin in coronary and renal arteries. In cholesterol-fed animals, the endothelium-dependent relaxations to aggregating platelets, adenosine diphosphate and serotonin were impaired in all four arteries. These experiments indicate that 1) the endothelium exerts inhibitory effects against aggregating platelets in porcine coronary and peripheral arteries; 2) platelet-induced endothelium-dependent relaxations are achieved by purinergic and 5-HT1-serotonergic receptors on the endothelium; and 3) hypercholesterolemia reduces the endothelium-dependent relaxations to aggregating platelets in a generalized manner because it impairs the relaxations to adenosine diphosphate and serotonin released from the platelets.
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PMID:Hypercholesterolemia causes generalized impairment of endothelium-dependent relaxation to aggregating platelets in porcine arteries. 278 7

The visual excitation system of the retinal rod outer segments and the hormone-sensitive adenylate cyclase complex are regulated through guanine nucleotide-binding proteins, transducin in the former and inhibitory and stimulatory regulatory components, Gi and Gs, in the latter. These proteins are functionally and structurally similar; all are heterotrimers composed of alpha, beta, and gamma subunits and exhibit guanosine triphosphatase activity stimulated by light-activated rhodopsin or the agonist-receptor complex. Adenylate cyclase can be stimulated by vanadate, which, like NaF, probably acts through Gs. Effects of vanadate on the function of a guanine nucleotide-binding protein were investigated in a reconstituted model system consisting of purified transducin subunits (T alpha, T beta gamma) and rhodopsin in phosphatidylcholine vesicles. Vanadate (decameric) inhibited [3H]GTP binding to T alpha and noncompetitively inhibited GTP hydrolysis in a concentration-dependent manner with maximal inhibition of approximately 90% at 3-5 mM. Vanadate also inhibited release of bound GDP but did not affect the rate of hydrolysis of bound GTP (single turnover rate), indicating that vanadate did not interfere with the intrinsic GTPase activity of T alpha. Binding of T alpha to rhodopsin and the ADP-ribosylation of T alpha by pertussis toxin, both of which are enhanced in the presence of T beta gamma, were inhibited by vanadate. These findings are consistent with the conclusion that vanadate can cause the dissociation of T alpha from T beta gamma, resulting in the inhibition of GDP-GTP exchange and thereby GTP hydrolysis. Adenylate cyclase activation could result from a similar effect of vanadate on Gs.
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PMID:Mechanism of inhibition of transducin guanosine triphosphatase activity by vanadate. 284 71

In the presence of Mg2+ the ecto-(nucleoside diphosphatase) on intact vascular endothelial or smooth muscle cells in culture selectively catabolizes the PS diastereoisomer of adenosine 5'-[alpha-thio]diphosphate, (PS)-ADP [alpha S], and the ecto-(nucleoside triphosphatase) selectively catabolizes the PS isomer of adenosine 5'-[beta-thio]triphosphate, (PR)-ATP[beta S], but exhibits no selectivity towards ATP[alpha S] isomers. In the presence of Cd2+ selectivity to ADP[alpha S] and to ATP[beta S] isomers is reversed; in the presence of Co2+, selectivity is lost. We conclude that each enzyme preferentially recognises the lambda (screw-sense) bidentate Mg(II)-nucleotide complex at its active site.
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PMID:Investigation of the preferred Mg(II)-adenine-nucleotide complex at the active site of ectonucleotidases in intact vascular cells using phosphorothioate analogues of ADP and ATP. 299 64

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.
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PMID:Ectonucleotidase activities associated with cholinergic synaptosomes isolated from Torpedo electric organ. 301 88

The role of the endothelium was examined in the response to aggregating platelets in cerebral arteries from normal and hypercholesterolemic animals. Male Yorkshire pigs were fed either a normal diet or a 2% high-cholesterol diet for 10 weeks. Endothelium-dependent responses were examined in vitro. In rings of basilar arteries from control animals aggregating platelets caused endothelium-dependent relaxations, which were significantly inhibited by apyrase, an adenosine diphosphatase and triphosphatase, but were augmented by methiothepin, a combined S1- and S2-serotonergic blocker. In quiescent rings platelets induced contractions that were inhibited by the presence of the endothelium; these contractions were significantly inhibited by methiothepin, but not by ketanserin (an S2-serotonergic blocker) or dazoxiben (a thromboxane-synthetase blocker) in the presence or absence of SQ29548 (a thromboxane-receptor blocker). Adenosine diphosphate but not serotonin caused endothelium-dependent relaxations. In cholesterol-fed animals the endothelium-dependent relaxations in response to aggregating platelets and adenosine diphosphate were impaired. These experiments indicate that 1) the endothelium inhibits the vasoconstrictor effect of aggregating platelets in porcine cerebral arteries; 2) platelet-induced relaxations are achieved mainly by a purinergic mechanism, while platelet-induced contractions are mediated by activation of S1-serotonergic receptors with little contribution of thromboxanes; and 3) hypercholesterolemia impairs the endothelium-dependent relaxations in response to aggregating platelets due to the impaired responses to adenosine diphosphate.
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PMID:Endothelium-dependent relaxation to aggregating platelets in isolated basilar arteries of control and hypercholesterolemic pigs. 340 91


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