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)

Electron histochemical studies show that changes in the nucleoside triphosphatase activity in plasma membranes of cancer cells can proceed in different directions. Some cells show a high activity of magnesium-dependent NTPase over the whole membrane surface (perimeter), while others have a low enzymic activity which is present only in certain regions of the membranes, the remaining cells possessing no enzyme activity at all. These changes are not strictly characteristic of cancer cells alone.
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PMID:Hydrolysis of nucleoside triphosphate in plasma membranes of the hepatocytes of normal, regenerating and foetal livers and in cancer cells of hepatomas. 19 42

The interaction of the Rev protein from human immunodeficiency virus type 1 (HIV-1) with the nucleocytoplasmic mRNA-transport system was investigated. In gel-shift assay, the recombinant Rev protein used in this study selectively bound to the Rev-responsive element (RRE) region of HIV-1 env-specific RNA. Nitrocellulose-filter-binding studies and Northern/Western-blotting experiments revealed an association constant of approximately 1 x 10(10) M-1. The Rev protein also strongly bound to isolated nuclear envelopes from H9 cells, containing the poly(A)-binding site (= mRNA carrier) and the nucleoside triphosphatase (= NTPase), which are thought to be involved in nuclear export of poly(A)-rich mRNA. Binding of 125I-Rev to a 110-kDa nuclear-envelope protein, the putative mRNA carrier, could be demonstrated in in vitro experiments. Both efflux of cellular poly(A)-rich RNA, such as actin RNA [but not efflux of poly(A)-free RNA] from isolated nuclei and the nuclear-envelope NTPase activity were strongly inhibited by Rev protein. On the other hand, transport of viral env RNA, containing the Rev-responsive element, was increased in the presence of Rev. Studying the release of RNA from closed nuclear-envelope vesicles containing entrapped RNA, the action of Rev was found to occur at the level of translocation of RNA through the nuclear pore. Evidence is presented that Rev down-regulates the NTPase-driven transport of mRNA lacking the RRE, most likely via binding to the mRNA carrier within the envelope. In contrast to the efflux of RRE-free RNA, ATP-dependent efflux of RRE-containing RNA from resealed nuclear-envelope vesicles was found to be increased, if the RNA was entrapped in the vesicles together with Rev protein. In addition, it was found that phosphorylated Rev, which is transported together with RRE-containing RNA out of the vesicles, becomes dephosphorylated during transport. In the vesicle experiments it is demonstrated for the first time that a protein selectively channels a specific mRNA across the nuclear-envelope pore complex.
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PMID:Evidence for a direct interaction of Rev protein with nuclear envelop mRNA-translocation system. 164 87

Acid nucleoside triphosphatase (Acid NTPase), an enzyme which catalyzes the hydrolysis of all nucleoside triphosphates to the corresponding diphosphates was purified from human serum with a purification factor of 190 and a recovery of 31%. The molecular weight was 75,000 as estimated by gel filtration. Gel-electrophoresis revealed an Rf-value of 0.11, and the isoelectric point was determined at pH 4.4. It exhibited a temperature optimum of 44 degrees C and the activation energy was estimated to be 41.6 kJ/mol. The enzyme was active in the absence of divalent cations, since activity was not inhibited by EDTA. The presence of this chelator reduced the Km-value from 70 to 40 microM. Inhibitor experiments revealed that tartrate was a weak mixed-type noncompetitive inhibitor, Ki = 88 mM. The enzyme was specific for the hydrolysis of nucleoside triphosphates. P-nitrophenyl phosphate was not accepted as a substrate. The enzyme revealed optimum activity at the exceptionally acid pH of 3.0. These unique characteristics indicate the presence of a novel enzyme.
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PMID:Acid nucleoside triphosphatase: partial purification and characterization of a new enzyme from human serum. 215 8

A study was made of the activity of nucleoside diphosphatase (NDPase, EC 3.6.1.16) and nucleoside triphosphatase (NTPase, EC 3.6.1.15) that catalyze enzymatic dephosphorylation of UDP, CDP, UTP, and CTP in mitochondria and postmitochondrial supernatant fraction of rat liver 30 min, 1, 3, 6 and 24 h following 60Co-gamma-irradiation with a dose of 774 mC/kg. The observed phase changes in the enzyme activity depended on the times of exposure, a cell fraction, and nucleotides under study. Both uridylic and cytidylic nucleotides exhibited a significant increase in the their enzymatic disintegration being more pronounced at a comparatively later times, that is, 6 h, and particularly, 24 h after irradiation.
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PMID:[Catabolism of pyrimidine nucleotides in the liver of irradiated animals]. 283 67

The genome of flaviviruses consists of an infectious single-stranded RNA molecule which contains a type 1 cap structure at the 5'-terminus. The cap is synthesized by RNA triphosphatase, guanylyltransferase and methyltransferase. Since flaviviruses replicate in the cytoplasm, it can be assumed that these functions are performed by virus-coded proteins. We previously showed that subtilisin treatment of membranes isolated from cells infected with the West Nile flavivirus results in release of a 50 kDa molecular weight fragment of the viral nonstructural protein NS 3. This so-called p50-S protein contains the residue gly (168) of NS 3 at the amino-terminus and represents an RNA-stimulated NTPase. In the present report we present experimental evidence which indicates that the p50-S protein also contains the active site of an RNA triphosphatase. The activity specifically cleaves the beta,gamma-triphosphate bond at the 5'-terminus of RNA. The localization of NS 3 protein sequence elements with known functions indicates that this multifunctional protein contains a protease in the amino-terminal part, a helicase in the central region and the RNA triphosphatase in the carboxy-terminal domain. An amino acid sequence element which may be involved in recognition of the 5'-terminal RNA triphosphate is tentatively identified. A homologous element may be present in the vaccinia virus-coded RNA triphosphatase.
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PMID:The NS 3 nonstructural protein of flaviviruses contains an RNA triphosphatase activity. 821 62

We investigated in vitro motility of F-actin on heavy meromyosin (HMM) and nucleotide triphosphatase activity of acto-HMM by using ATP analogues of various nucleotide triphosphates (NTPs) and enzymatically cleaved actins. The sliding velocity did not correlate with the actin activated HMM-NTPase activity, but correlated strongly with the reciprocal of NTPase activity of HMM itself, i.e., the cycle time of HMM NTPase. This indicated that with ATP the complex of myosin with the product, M.ADP.Pi, at the long lived intermediate state of the rate limiting step would play a key role for efficient mechanochemical energy transduction during actin-myosin interaction.
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PMID:The mechanism for mechanochemical energy transduction in actin-myosin interaction revealed by in vitro motility assay with ATP analogues. 863 37

The NS3 protein of flaviviruses is a multifunctional polypeptide required for virus replication. Enzymic activities that have been demonstrated or predicted from the presence of sequence motifs include protease, NTPase, helicase and RNA triphosphatase. Both full-length and truncated forms of NS3 have been identified in infected cells. To examine internal cleavage of the NS3 protein of dengue virus 2 (DEN-2), infected cells or COS cells transfected with cDNA encoding NS2B/3 were radiolabelled and immunoprecipitated with antiserum against NS3 or hyperimmune mouse ascitic fluid. The polypeptides detected were NS2B/3 (Mr 83000), NS3 (Mr 69000), NS3' (Mr 50000) and NS3" (Mr 19000). The latter polypeptide has not been previously identified. For DEN-2, it has been proposed that NS3' results from cleavage at the site ...R457R / GR460... within an RNA helicase sequence motif of NS3. Our results demonstrated that cleavage occurred at this site, and that prior cleavage between NS2B/NS3 was not necessary.
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PMID:Internal proteolysis of the NS3 protein specified by dengue virus 2. 901 55

Saccharomyces cerevisiae Cet1p is the prototype of a family of metal-dependent RNA 5'-triphosphatases/NTPases encoded by fungi and DNA viruses; the family is defined by conserved sequence motifs A, B, and C. We tested the effects of 12 alanine substitutions and 16 conservative modifications at 18 positions of the motifs. Eight residues were identified as important for triphosphatase activity. These were Glu-305, Glu-307, and Phe-310 in motif A (IELEMKF); Arg-454 and Lys-456 in motif B (RTK); Glu-492, Glu-494, and Glu-496 in motif C (EVELE). Four acidic residues, Glu-305, Glu-307, Glu-494, and Glu-496, may comprise the metal-binding site(s), insofar as their replacement by glutamine inactivated Cet1p. E492Q retained triphosphatase activity. Basic residues Arg-454 and Lys-456 in motif B are implicated in binding to the 5'-triphosphate. Changing Arg-454 to alanine or glutamine resulted in a 30-fold increase in the K(m) for ATP, whereas substitution with lysine increased K(m) 6-fold. Changing Lys-456 to alanine or glutamine increased K(m) an order of magnitude; ATP binding was restored when arginine was introduced. Alanine in lieu of Phe-310 inactivated Cet1p, whereas Tyr or Leu restored function. Alanine mutations at aliphatic residues Leu-306, Val-493, and Leu-495 resulted in thermal instability in vivo and in vitro. A second S. cerevisiae RNA triphosphatase/NTPase (named Cth1p) containing motifs A, B, and C was identified and characterized. Cth1p activity was abolished by E87A and E89A mutations in motif A. Cth1p is nonessential for yeast growth and, by itself, cannot fulfill the essential role played by Cet1p in vivo. Yet, fusion of Cth1p in cis to the guanylyltransferase domain of mammalian capping enzyme allowed Cth1p to complement growth of cet1Delta yeast cells. This finding illustrates that mammalian guanylyltransferase can be used as a vehicle to deliver enzymes to nascent pre-mRNAs in vivo, most likely through its binding to the phosphorylated CTD of RNA polymerase II.
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PMID:Mutational analyses of yeast RNA triphosphatases highlight a common mechanism of metal-dependent NTP hydrolysis and a means of targeting enzymes to pre-mRNAs in vivo by fusion to the guanylyltransferase component of the capping apparatus. 1050 29

The RNA triphosphatase component (CaCet1p) of the mRNA capping apparatus of the pathogenic fungus Candida albicans differs mechanistically and structurally from the RNA triphosphatase of mammals. Hence, CaCet1p is an attractive antifungal target. Here we identify a C-terminal catalytic domain of CaCet1p from residue 257 to 520 and characterize a manganese-dependent and cobalt-dependent NTPase activity intrinsic to CaCet1p. The NTPase can be exploited to screen in vitro for inhibitors. The amino acids that comprise the active site of CaCet1p were identified by alanine-scanning mutagenesis, which was guided by the crystal structure of the homologous RNA triphosphatase from Saccharomyces cerevisiae (Cet1p). Thirteen residues required for the phosphohydrolase activity of CaCet1p (Glu287, Glu289, Asp363, Arg379, Lys396, Glu420, Arg441, Lys443, Arg445, Asp458, Glu472, Glu474 and Glu476) are located within the hydrophilic interior of an eight-strand beta barrel of Cet1p. Each of the eight strands contributes at least one essential amino acid. The essential CaCet1p residues include all of the side chains that coordinate manganese and sulfate (i.e., gamma phosphate) in the Cet1p product complex. These results suggest that the active site structure and catalytic mechanism are conserved among fungal RNA triphosphatases.
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PMID:Characterization of Candida albicans RNA triphosphatase and mutational analysis of its active site. 1075 87

Severe acute respiratory syndrome coronavirus (SARS-CoV), a newly identified group 2 coronavirus, is the causative agent of severe acute respiratory syndrome, a life-threatening form of pneumonia in humans. Coronavirus replication and transcription are highly specialized processes of cytoplasmic RNA synthesis that localize to virus-induced membrane structures and were recently proposed to involve a complex enzymatic machinery that, besides RNA-dependent RNA polymerase, helicase, and protease activities, also involves a series of RNA-processing enzymes that are not found in most other RNA virus families. Here, we characterized the enzymatic activities of a recombinant form of the SARS-CoV helicase (nonstructural protein [nsp] 13), a superfamily 1 helicase with an N-terminal zinc-binding domain. We report that nsp13 has both RNA and DNA duplex-unwinding activities. SARS-CoV nsp13 unwinds its substrates in a 5'-to-3' direction and features a remarkable processivity, allowing efficient strand separation of extended regions of double-stranded RNA and DNA. Characterization of the nsp13-associated (deoxy)nucleoside triphosphatase ([dNTPase) activities revealed that all natural nucleotides and deoxynucleotides are substrates of nsp13, with ATP, dATP, and GTP being hydrolyzed slightly more efficiently than other nucleotides. Furthermore, we established an RNA 5'-triphosphatase activity for the SARS-CoV nsp13 helicase which may be involved in the formation of the 5' cap structure of viral RNAs. The data suggest that the (d)NTPase and RNA 5'-triphosphatase activities of nsp13 have a common active site. Finally, we established that, in SARS-CoV-infected Vero E6 cells, nsp13 localizes to membranes that appear to be derived from the endoplasmic reticulum and are the likely site of SARS-CoV RNA synthesis.
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PMID:Multiple enzymatic activities associated with severe acute respiratory syndrome coronavirus helicase. 1514 Sep 59


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