- Dinuclear Zn2+ complexes in the hydrolysis of the phosphodiester linkage in a diribonucleoside monophosphate diester.
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Dizinc complexes that were formed from 2:1 mixtures of Zn(NO3)2 and dinucleating ligands TPHP (1), TPmX (2) or TPpX (3) in aqueous solutions efficiently hydrolyzed diribonucleoside monophosphate diesters (NpN) under mild conditions. The dinucleating ligand affected the structure of the aquo-hydroxo-dizinc core, resulting in different characteristics in the catalytic activities towards NpN cleavage. The pH-rate profile of ApA cleavage in the presence of (Zn2+)(2)-1 was sigmoidal, whereas those of (Zn2+)(2)-2 and (Zn2+)(2)-3 were bell-shaped. The pH titration study indicated that (Zn2+)(2)-1 dissociates only one aquo proton (up to pH 12), whereas (Zn2+)(2)-2 dissociates three aquo protons (up to pH 10.7). The observed differences in the pH-rate profile are attributable to the various distributions of the monohydroxo-dizinc species, which are responsible for NpN cleavage. As compared to that using (Zn2+)(2)-1, the NpN cleavage using (Zn2+)(2)-2 showed a greater rate constant, with a higher product ratio of 3'-NMP/2'-NMP. The saturation behaviors of the rate, with regard to the concentration of NpN, were analyzed by Michaelis-Menten type kinetics. Although the binding of (Zn2+)(2)-2 to ApA was weaker than that of (Zn2+)(2)-1, (Zn2+)(2)-2 showed a greater kcat value than (Zn2+)(2)-1, resulting in higher ApA cleavage activity of the former.
- Yashiro, Morio,Kaneiwa, Hideki,Onaka, Kenichi,Komiyama, Makoto
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p. 605 - 610
(2007/10/03)
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- The pKa of the internucleotidic 2′-hydroxyl group in diribonucleoside (3′→5′) monophosphates
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Ionization of the internucleotidic 2′-hydroxyl group in RNA facilitates transesterification reactions in Group I and II introns (splicing), hammerhead and hairpin ribozymes, self-cleavage in lariatRNA, and leadzymes and tRNA processing by RNase P RNA, as well as in some RNA cleavage reactions promoted by ribonucleases. Earlier, the pKa of 2′-OH in mono- and diribonucleoside (3′-5′) monophosphates had been measured under various nonuniform conditions, which make their comparison difficult. This work overcomes this limitation by measuring the pKa values for internucleotidic 2′-OH of eight different diribonucleoside (3′-5′) monophosphates under a set of uniform noninvasive conditions by 1H NMR. Thus the pKa is 12.31 (±0.02) for ApG and 12.41 (±0.04) for ApA, 12.73 (±0.04) for GpG and 12.71 (±0.08) for GpA, 12.77 (±0.03) for CpG and 12.88 (±0.02) for CpA, and 12.76 (±0.03) for UpG and 12.70 (±0.03) for UpA. By comparing the pKas of the respective 2′-OH of monomeric nucleoside 3′-ethyl phosphates with that of internucleotidic 2′-OH in corresponding diribonucleoside (3′→5′) monophosphates, it has been confirmed that the aglycons have no significant effect on the pKa values of their 2′-OH under our measurement condition, except for the internucleotidic 2′-OH of 9-adeninyl nucleotide at the 5′-end (ApA and ApG), which is more acidic by 0.3-0.4 pKα units.
- Acharya,Foeldesi,Chattopadhyaya
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p. 1906 - 1910
(2007/10/03)
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- Phosphodiester Cleavage of Ribonucleoside Monophosphates and Polyribonucleotides by Homo- and Heterodinuclear Metal Complexes of a Cyclohexane-Based Polyamino-Polyol Ligand
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The ability of the dinuclear complexes of tdci [1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol] to promote the cleavage of the phosphodiester bonds of nucleoside 2′,3′-cyclic monophosphates, dinucleoside monophosphates and polyribonucleotides has been studied. The homodinuclear copper(II) and zinc(II) complexes efficiently promote the hydrolysis of cyclic nucleotides. The second-order rate constant (k2≈0.44M-1S-1) estimated for the cleavage of 2′,3′-cAMP induced by dinuclear copper(II) complexes is about 107 times greater than that for the hydroxide-ion-catalysed reaction. The complex selectively cleaves the 2′O-P bond of 2′,3′-cUMP and forms the 3′-product in 91% yield. An equimolar mixture of copper(II), zinc(II) and tdci proved to be more efficient than either of the binary systems: a 7-20-fold rate enhancement was observed for the cleavage of 2′,3′-cNMP substrates. The half-life for the hydrolysis of 2′,3′-cAMP decreased from 300 days to five minutes at 25°C when the concentration of each of the three components was 2.5mM. In contrast to the copper(II) or zinc(II) complexes of tdci, the heterodinuclear species promoted the hydrolysis of several dinucleoside monophosphates. For two ApA isomers, cleavage of the 3′,5′-bond was about 6.5 times faster than cleavage of the 2′,5′-bond. On the basis of the kinetic data, a trifunctional mechanism is suggested for the heterodinuclear-complex-promoted cleavage of the phosphodiester bond. Double Lewis acid activation occurs when the metal ions bind to the phosphate oxygen atoms. In particular, a metal-bound hydroxide ion serves as a general base or a nucleophilic catalyst, and, presumably, a zinc(II)-bound aqua ligand behaves as a general acid and facilitates the departure of the leaving alkoxide group. The effect of the complexes on the hydrolysis of poly(U), poly(A) and type III native RNA was also investigated, and, for the first time, kinetic data on the cleavage of the phosphodiester bonds of polyribonucleotides by a dinuclear complex was obtained.
- Jancso, Attila,Mikkola, Satu,Loennberg, Harri,Hegetschweiler, Kaspar,Gajda, Tamas
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p. 5404 - 5415
(2007/10/03)
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- Rapid and highly base selective RNA cleavage by a dinuclear Cu(II) complex
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A bis-Cu(II) complex based on a covalently linked terpyridine and bipyridine ligand system is shown to rapidly cleave bis-ribonucleotides with remarkable selectivity for adenine bases.
- Liu, Shanghao,Hamilton, Andrew D.
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p. 587 - 588
(2007/10/03)
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- Efficient RNA hydrolysis by lanthanide(III)-hydrogen peroxide combinations. Novel aggregates as the catalytic species
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Combinations of lanthanum(III) ion and hydrogen peroxide efficiently hydrolyze RNA under physiological conditions, because of a synergetic cooperation. The rate constant for the hydrolysis of adenylyl(3′-5′)adenosine at pH 7.2 and 30°C is 7.7 x 10-2 min-1, when [LaIII]0 = 10 and [H2O2]0 = 100 mM. This value is 460 times as great as that for the ApA hydrolysis by La alone (1.7 x 10-4 min-1). Hydrogen peroxide is inactive when used separately. A similar synergism operates between NdIII and H2O2. According to the kinetic analysis and the potentiometric titration, a trimeric aggregate of [La(O-O)3La] complex is responsible for the RNA hydrolysis. This result is in contrast with the previous proposal on the hydrolysis of bis(4-nitrophenyl)phosphate that monomeric species of [La(O-O)2La]2+ is the active species (B. K. Takasaki and J. Chin, J. Am. Chem. Soc., 1995, 117, 8582). The discrepancy is ascribed to the difference in the basicities of the leaving groups in the substrates.
- Kamitani, Jun,Sumaoka, Jun,Asanuma, Hiroyuki,Komiyama, Makoto
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p. 523 - 527
(2007/10/03)
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- Rapid and highly selective cleavage of ribonucleoside 2',3'-cyclic monophosphates by dinuclear Cu(II) complexes
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Two characteristics that never before appeared together are combined in complexes 1 and 2, which show high activity and high selectivity in the hydrolysis of cyclic nucleoside 2',3'-monophosphates as model compounds for RNA. In the case of 1 the regioselectivity is exceptional, and, in the case of 2, the base selectivity.
- Liu,Luo,Hamilton
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p. 2678 - 2680
(2007/10/03)
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- Additional Evidence for the Exceptional Mechanism of the Acid-catalysed Hydrolysis of 4-Oxopyrimidine Nucleosides: Hydrolysis of 1-(1-Alkoxyalkyl)uracils, Seconucleosides, 3'-C-Alkyl Nucleosides and Nucleoside 3',5'-Cyclic Monophosphates
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The rate constants for the acid-catalysed hydrolysis of 1-(1-alkoxyethyl)uracils and 1-alkoxymethyluracils have been determined.With both series of compounds, the hydrolysis rate is rather insensitive to the polar nature of the alkoxy group, in striking contrast with the hydrolysis of the corresponding analogues of adenine and cytosine nucleosides, which react via rate-limiting formation of an oxocarbenium ion intermediate.Furthermore, it has been shown that 3',5'-cyclic monophosphates of thymidine and uridine undergo hydrolysis of the N-glycosidic bond 760 and 260 times as fast as their parent nucleosides, while the cyclic monophosphates of 2'-deoxyadenosine and adenosine are depurinated much more slowly than the corresponding nucleosides.On this basis it is suggested that 4-oxopyrimidine nucleosides are hydrolysed by opening of the sugar ring.To obtain further evidence for this exceptional mechanism, comparative kinetic measurements with some seco- and 3'-C-alkyl nucleosides of uracil and adenine have been carried out.
- Oivanen, Mikko,Rajamaeki, Markku,Varila, Jaana,Hovinen, Jari,Mikhailov, Sergey,Loennberg, Harri
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p. 309 - 314
(2007/10/02)
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- Water-Soluble Calixarene as the First Man-Made Catalyst for Regioselective Cleavage of Ribonucleoside 2',3'-Cyclic Phosphate
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The P-O(2') bond of cytidine 2',3'-cyclic phosphate, an intermediate in RNA hydrolysis, is regioselectively cleaved at pH 2 by use of water-soluble calixarene-5,11,17,23-tetrasulfonate.This is the first totally man-made mimic for the regioselective catalysis of ribonuclease.
- Komiyama, Makoto,Isaka, Kazuhiro,Shinkai, Seiji
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p. 937 - 940
(2007/10/02)
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- Kinetics of Reactions of Pyrimidine Nucleoside 2'- and 3'-Monophosphates under Acidic and Neutral Conditions: Concurrent Phosphate Migration, Dephosphorylation and Deamination
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First-order rate constants for the following reactions of cytidine and uridine monophosphates have been determined over the activity range from pH 7 to H0 -0.7: (i) interconversion of the 2'- and 3'-monophosphates of cytidine and uridine, (ii) dephosphorylation of the 2'-, and 3'- and 5'-monophosphates, and (iii) deamination of cytosine nucleotides to uracil nucleotides.Competition between these reactions under various conditions is discussed, and the data on phosphate migration and phosphoester hydrolysis are compared with those reported earlier for adenosine monophosphates.
- Oivanen, Mikko,Loennberg, Harri
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p. 239 - 242
(2007/10/02)
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- Regioselective P-O(2') Cleaveage of Cytidine 2',3'-Cyclic Monophosphate Catalyzed by α-Cyclodextrin
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Regioselective cleavage (selectivity 98percent) of the P-O(2') bond of cytidine 2',3'-cyclic monophosphate is carried out at pH 11.08, 20 deg C by use of α-cylodextrin as catalyst.Without α-cyclodextrin, the selectivity is only 47percent due to concurrent cleavage of the P-O(3') bond.The regioselective catalysis is ascribed to the formation of a complex between α-cyclodextrin and the monophosphate.
- Komiyama, Makoto
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p. 1121 - 1124
(2007/10/02)
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- IMMUNOAFFINITY PURIFICATION OF CYCLIC NUCLEOTIDE PHOSPHODIESTERASE FROM LACTUCA COTYLEDONS
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To facilitate further study of a multifunctional phosphodiesterase, previously partially purified from Lactuca cotyledons, a new purification step has been devised.This uses an immunoaffinity column based upon polyclonal antibodies raised against the partially purified enzyme.Preparation of the immunoaffinity column, purufication of the enzyme using the new protocol, and analysis of the activity of the purified enzyme are described.The additional step produced an enzyme preparation with a significantly higher specific activity and free of nucleotidase and non-specific phosphatase activity.The observed properties of the enzyme confirm similarities with mammalian multifunctional phosphodiesterase but reaffirm the existence of two types of substrate binding site on the Lactuca phosphodiesterase.Key Word Index - Lactuca sativa; Compositae; lettuce; cotyledons; cyclic nucleotides; phosphodiesterase; immunoaffinity purification; 3',5'-cyclic AMP; 3',5'-cyclic GMP; 3',5'-cyclic CMP; 3',5'-cyclic UMP.
- Chiatante, Donato,Balconi, Carlotta,Newton, Russell P.,Brown, Eric G.
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p. 2477 - 2484
(2007/10/02)
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- DECYCLIZING PHOSPHODIESTERASES ASSOCIATED WITH PLASMA MEMBRANES OF THE CHICK CHORIOALANTOIS
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Two different enzymatic activities hydrolyzing 2',3'-cyclic phosphates of purine and pyrimidine ribonucleosides to give 2'- or 3'-ribonucleotides have been detected in plasma membranes of the chick chorioalantois.The enzymes differ in their temperature optima: At lower temperatures, cleavage to the 2'-isomers predominates.
- Pristasova, Svetlana,Rosenbergova, Marta,Holy, Antonin
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p. 520 - 524
(2007/10/02)
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