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PubMed2001

Stabilities and isomeric equilibria in solutions of monomeric metal-ion complexes of guanosine 5'-triphosphate (GTP4-) and inosine 5'-triphosphate (ITP4-) in comparison with those of adenosine 5'-triphosphate (ATP4-).

Under experimental conditions in which the self-association of the purine-nucleoside 5'-triphosphates (PuNTPs) GTP and ITP is negligible, potentiometric pH titrations were carried out to determine the stabilities of the M(H;PuNTP) and M(PuNTP)2-complexes where M2+ = Mg2+, Ca2+, Sr2+. Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+ (I = 0.1 M, 25 degrees C). The stabilities of all M(GTP)2- and M(ITP)2- complexes are significantly larger than those of the corresponding complexes formed with pyrimidine-nucleoside 5'-triphosphates (PyNTPs), which had been determined previously under the same conditions. This increased complex stability is attributed, in agreement with previous 1H MNR shift studies, to the formation of macrochelates of the phosphate-coordinated metal ions with N7 of the purine residues. A similar enhanced stability (despite relatively large error limits) was observed for the M(H;PuNTP) complexes, in which H+ is bound to the terminal y-phosphate group, relative to the stability of the M(H;PyNTP)- species. The percentage of the macrochelated isomers in the M(GTP)2- and M(ITP)2- systems was quantified by employing the difference log KMM(PuNTP)-log KMM(PyNTP); the lowest and highest formation degrees of the macrochelates were observed for Mg(ITP)2- and Cu(GTP)2- with 17 +/- 11% and 97 +/- 1%, respectively. From previous studies of M(ATP)2- complexes, it is known that innersphere and outersphere macrochelates may form; that is, in the latter case a water molecule is between N7 and the phosphate-coordinated M2+. Similar conclusions are reached now by comparisons with earlier 1H MNR shift measurements, that is, that Mg(GTP)2- (21 +/- 11%), for example, exists largely in the form of an outersphere macrochelate and Zn(GTP)2- (68 +/- 4%) as an innersphere one. Generally, the overall percentage of macrochelate falls off for a given metal ion in the order M(GTP)2- > M(ITP)2- > M(ATP)2-; this is in accord with the decreasing basicity of N7 and the steric inhibition of the (C6)NH2 group in the adenine residue. Furthermore, although the absolute stability constants of the previously studied M(GMP), M(IMP), and M(AMP) complexes differ by about two to three log units from the present M(PuNTP)2- results, the formation degrees of the macrochelates are astonishingly similar for the two series of nucleotides for a given metal ion and purine-nucleobase residue. The conclusion that N7 of the guanine residue is an especially favored binding site for metal ions is also in accord with observations made for nucleic acids.

Adenosine Triphosphate↗
PubMed1970

Localization of adenosine triphosphatase activity on the chloroplast envelope in tendrils of Pisum sativum.

When samples of pea tendril tissue were incubated in the Wachstein-Meisel medium for the demonstration of adenosine triphosphatases, deposits of lead reaction product were localized between the membranes of the chloroplast envelope. The presence of Mg(2+) was necessary for adenosine triphosphatase activity, and Ca(2+) could not substitute for this requirement. Varying the pH of incubation to 5.5 or 9.4 inhibited enzyme activity, as did the addition of p-chloromercuribenzoic acid or N-ethylmaleimide. The adenosine triphosphatase was apparently inactivated or degraded when the plants were grown in the dark for 24 hours prior to incubation. The enzyme was substrate-specific for adenosine triphosphate; no reaction was obtained with adenosine diphosphate, uridine triphosphate, inosine triphosphate, p-nitrophenyl phosphate, and sodium beta-glycerophosphate. Sites of nonspecific depositions of lead are described. The adenosine triphosphatase on the chloroplast envelope may be involved in the light-induced contraction of this organelle.

Adenosine Triphosphatases↗
PubMed1976

A comparison of ATP-degrading enzyme activities in rat incisor odontoblasts.

In active odontoblasts from the rat incisor, used as a model system for biologic calcification, two distinguishable enzyme activities capable of degrading adenosine monophosphate (ATP) exist. Once can be inhibited ny 1-tetramisole, (+/-)-2,3,5,6,-tetrahydro-6-phenylimidazo (2.1B) THIAZOLE HYDROCHLORIDE (Levamisol) and (+/-)-6(m-bromophenyl)-5.6-dehydroimidazo (2.1-b) thiazole oxalate (R823) and is probably identical with nonspecific alkaline phosphatase (EC 3.1.3.1). The activity of the other enzyme, named Ca2+-ATPase, is dependent on the presence of Ca2+ or Mg2+ and is activated by these ions. The pH optimum of Ca2+-ATPase is 9.8. The Ca2+-ATPase is unaffected by Levamisole, R 8231, ouabain, ruthenium red, Na+ and K+ ions. Maximal activity was found against ATP, whereas adenosine diphosphate, guanosine triphosphate, inosine triphosphate and adensoine monophosphate were hydrolysed at lower rate. It may be speculated that the Ca2+-ATPase is concerned with the transmembranous transport of Ca2+ ions to the mineralization front.

Adenosine Triphosphatases↗
PubMed1992

Effect of nucleotide cofactor structure on recA protein-promoted DNA pairing. 2. DNA renaturation reaction.

We have examined the effects of the structurally related nucleoside triphosphates, adenosine triphosphate (ATP), purine riboside triphosphate (PTP), inosine triphosphate (ITP), and guanosine triphosphate (GTP), on the recA protein-promoted DNA renaturation reaction (phi X DNA). In the absence of nucleotide cofactor, the recA protein first converts the complementary single strands into unit-length duplex DNA and other relatively small paired DNA species; these initial products are then slowly converted into more complex multipaired network DNA products. ATP and PTP stimulate the conversion of initial product DNA into network DNA, whereas ITP and GTP completely suppress network DNA formation. The formation of network DNA is also inhibited by all four of the corresponding nucleoside diphosphates, ADP, PDP, IDP, and GDP. Those nucleotides which stimulate the formation of network DNA are found to enhance the formation of large recA-ssDNA aggregates, whereas those which inhibit network DNA formation cause the dissociation of these nucleoprotein aggregates. These results not only implicate the nucleoprotein aggregates as intermediates in the formation of network DNA, but also establish the functional equivalency of ITP and GTP with the nucleoside diphosphates. Additional experiments indicate that the net effect of ITP and GTP on the DNA renaturation reaction is dominated by the corresponding nucleoside diphosphates, IDP and GDP, that are generated by the NTP hydrolysis activity of the recA protein.

Adenosine Triphosphate↗
PubMed1979

Calcium regulation in chicken gizzard muscle and inosine triphosphate-induced superprecipitation of skeletal acto-gizzard myosin.

Inosine triphosphate (ITP) does not serve as a substrate for myosin light-chain kinase from gizzard muscle. That is to say, myosin light-chain is not phosphorylated in ITP media. Nevertheless, at pH 6.8, 1 mM or 5 mM ITP induces superprecipitation of skeletal acto-gizzard myosin. The ITP-induced superprecipitation occurs in the absence or presence of calcium ions, and regardless of whether gizzard myosin is phosphorylated or not. On the other hand, at pH 8, 5 MM ITP induces practically no superprecipitation of skeletal acto-gizzard unphosphorylated myosin, whereas it does induce a strong superprecipitation of skeletal acto-gizzard phosphorylated myosin. Superprecipitation is also independent of the presence or absence of calcium ions.

Actins↗
PubMed1980

Initiation of reovirus transcription by inosine 5'-triphosphate and properties of 7-methylinosine-capped, inosine-substituted messenger ribonucleic acids.

Inosine 5'-triphosphate (ITP) can be utilized in place of guanosine 5'-triphosphate (GTP) for both the initiation and the elongation steps of reovirus transcription, resulting in the synthesis of mRNAs containing 5'-terminal m7IpppIm and internal pI. The apparent molecular weights of the I-substituted products were altered as a consequence of the absence of G-C base pairs and accompanying loss of ordered structure. The migration of I-substituted RNAs in agarose gels and glycerol gradients was similar to glyoxal-treated transcripts; i.e., it decreased 2-fold as compared to the corresponding untreated G-containing mRNAs. 7-Methylinosine-capped (m7I-capped), I-substituted transcripts readily attached to wheat germ 80S ribosomes. Unlike native G-containing mRNAs, they also formed heavier complexes that sedimented faster than 80S complexes even in the presence of the nonhydrolyzable ATP analogue AMPP(NH)P and elongation inhibitor sparsomycin. I-substituted molecules that were capped posttranscriptionally to form m7G-capped 5' ends yielded mostly 80S monosomes, consistent with a strong influence of 5'-terminal structure on initiation of translation. Under limited conditions of initiation, I-substituted RNAs outcompeted G-containing transcripts for ribosome attachment. Although the results are consistent with enhanced binding and freer movement of ribosomes on unstructured templates, synthesis of acid-precipitable polypeptides in wheat germ extract directed by I-substituted RNAs was 15-fold less than with G-containing mRNAs.

Binding Sites↗
PubMed1992

Effect of nucleotide cofactor structure on recA protein-promoted DNA pairing. 1. Three-strand exchange reaction.

The structurally related nucleoside triphosphates, adenosine triphosphate (ATP), purine riboside triphosphate (PTP), inosine triphosphate (ITP), and guanosine triphosphate (GTP), are all hydrolyzed by the recA protein with the same turnover number (17.5 min-1). The S0.5 values for these nucleotides increase progressively in the order ATP (45 microM), PTP (100 microM), ITP (300 microM), and GTP (750 microM). PTP, ITP, and GTP are each competitive inhibitors of recA protein-catalyzed ssDNA-dependent ATP hydrolysis, indicating that these nucleotides all compete for the same catalytic site on the recA protein. Despite these similarities, ATP and PTP function as cofactors for the recA protein-promoted three-strand exchange reaction, whereas ITP and GTP are inactive as cofactors. The strand exchange activity of the various nucleotides correlates directly with their ability to support the isomerization of the recA protein to a strand exchange-active conformational state. The mechanistic deficiency of ITP and GTP appears to arise as a consequence of the hydrolysis of these nucleotides to the corresponding nucleoside diphosphates, IDP and GDP. We speculate the nucleoside triphosphates with S0.5 values greater than 100 microM will be intrinsically unable to sustain the strand exchange-active conformational state of the recA protein during ongoing NTP hydrolysis and will therefore be inactive as cofactors for the strand exchange reaction.

Adenosine Triphosphate↗
PubMed1990

Clastogenic inosine nucleotide as components of the chromosome breakage factor in scleroderma patients.

In the present study, we attempted to identify the chemical nature of the clastogenic factor (CF) from patients with progressive systemic sclerosis (scleroderma). Computerized mass spectrometry of clastogenic fractions obtained by HPLC of plasma ultrafiltrates detected molecular peaks compatible with inosine triphosphate and inosine diphosphate (ITP and IDP). The concomitant detection of IDP, together with ITP, and the absence of these peaks in nonclastogenic fractions and corresponding control fractions are arguments in favor of a biological relevance of these observations. The most important confirmation came from the clastogenic effect of commercial ITP and IDP added to the culture medium of the test cultures. The induction of chromatid type damage by these substances in lymphocytes exposed in the G0 phase of their cell cycle and the prevention of this damage by superoxide dismutase are analogous to the observations with CF.

Cells, Cultured↗
PubMed1991

Regulation of permeabilized endothelial cell retraction by myosin phosphorylation.

Permeabilized endothelial cell monolayers retracted on exposure to ATP and Ca2+. ADP, inosine triphosphate (ITP), GTP, adenosine 5'-(gamma-thio)triphosphate (ATP-gamma S), and 5'-adenylylimidodiphosphate failed to support retraction. However, ATP gamma S, a substrate for myosin light-chain kinase (MLCK) but not myosin adenosinetriphosphatase (ATPase), combined with ITP, a substrate for myosin ATPase but not MLCK, supported retraction. Two MLCK pseudosubstrate peptides, M5 and SM-1, inhibited endothelial cell retraction equally and more effectively than myosin kinase-inhibitory peptide with a sequence based on the phosphorylated site of myosin light chain. M5 was shown to inhibit thiophosphorylation of endothelial cell myosin light chains. Endothelial cells incubated with exogenous unregulated kinase in the presence of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid retracted on addition of ATP. This retraction was accompanied by thiophosphorylation of the 19 kDa myosin light chains in the presence of ATP gamma 35S. The N-ethylmaleimide-modified subfragment 1 of myosin heads, a specific inhibitor of actin-myosin interaction, prevented retraction. These data add support to the proposal of a central role for MLCK activation of myosin in endothelial retraction.

Adenosine Triphosphate↗
PubMed2006

Pancytopenia due to high 6-methylmercaptopurine levels in a 6-mercaptopurine treated patient with Crohn's disease.

In a 23-year-old female with colonic Crohn's disease 6-mercaptopurine 100 mg daily (1.7 mg/kg) was added to mesalamine and prednisolone therapy because of ongoing disease activity. One month later she had fever and a pancytopenia. 6-methylmercaptopurine ribonucleotides levels were extremely elevated (57,000 pmol/8x10(8) red blood cells) and 6-thioguanine nucleotides levels were subtherapeutically (126 pmol/8x10(8) red blood cells). Genotyping showed a wildtype thiopurine S-methyltransferase TPMT(H/H) (*1/*1) genotype and a wildtype inosine triphosphate pyrophosphatase gene. TPMT and inosine triphosphate pyrophosphatase activity were normal. The pancytopenia recovered spontaneously within a few weeks, parallel with decreasing 6-methylmercaptopurine ribonucleotides levels after interrupting 6-mercaptopurine treatment. Epstein-Barrvirus, Cytomegalovirus and Herpesvirus infections were excluded by serology. This is the first report of pancytopenia due to extremely high 6-methylmercaptopurine ribonucleotides levels. No relation was found with the genotype of TPMT and inosine triphosphate pyrophosphatase enzymes, which play key roles in the thiopurine metabolic pathway. Apparently, 6-methylmercaptopurine ribonucleotides metabolites can cause pancytopenia, as was already known for 6-thioguanine nucleotides.

Adult↗
PubMed1985

Characterization of the kinetic and regulatory properties of high-affinity Ca2+-ATPase activity in acinar preparations of rat submandibular salivary glands.

High-affinity Ca2+-ATPase activity was characterized in the total particulate fraction of acinar preparations from rat submandibular glands. The Ca2+ concentration (as Ca2+-ATP) at half of maximal activity was 82 +/- 17 nM, the Hill coefficient was 2.36 +/- 0.6 and activity reached a steady level at approximately 200 pmol Pi min-1 microgram of membrane protein-1 from 1 to 20 microM Ca2+-ATP. High-affinity Ca2+-ATPase required micromolar concentrations of Mg2+ and was inhibited approximately 60 per cent by the phenothiazine derivative, fluphenazine, but was unaffected by ouabain, Na+, K+, La3+, ruthenium red, oligomycin and added calmodulin. Kinetics of adenosine diphosphate, guanosine triphosphate, uridine triphosphate and inosine triphosphate hydrolysis were similar to those of Ca2+-ATP but p-nitrophenylphosphate was a poor substrate. In the heavy microsomal fraction of whole glands, active Ca2+ uptake (ATP-dependent, oxalate-enhanced and abolished by A23187) was measurable in the absence of added Mg2+, was inhibited by fluphenazine and was stimulated by submicromolar concentrations of Ca2+-ATP. Thus rat submandibular glands contain the enzymic basis of active Ca2+ transport and can actively transport Ca2+. Both activities are stimulated at Ca2+ concentrations typical of the cytosol, appear to be positively cooperative and may be regulated, in part, by calmodulin.

Adenosine Triphosphate↗