Non-Enzymatic RNA Hydrolysis Promoted by the Combined Catalytic Activity of Buffers and Magnesium Ions

1999 ◽  
Vol 54 (7-8) ◽  
pp. 542-548 ◽  
Author(s):  
Mounir G. AbouHaidar ◽  
Ivan G. Ivanov
Keyword(s):  
Catalytic Activity ◽  
Chelating Agents ◽  
Rna Degradation ◽  
Sodium Borate ◽  
Ph Values ◽  
Principal Factors ◽  
Chemical Nuclease ◽  
Rna Hydrolysis ◽  
Specific Degradation ◽  
Soluble Material

Abstract Although Mg2+ is an important cofactor for the specific degradation of RNA by ribozymes, it is not considered as a typical chemical nuclease. In this study we show that in combination with common buffers such as tris(hydroxymethyl)aminomethane and sodium borate. Mg2+ is a powerful catalyst for the degradation of RNA. pH and temperature are found to be the principal factors for the efficient degradation of RNA. Whereas in Tris-HCl/Mg2+ the effi­cient cleavage starts at pH values higher than 7.5 and temperatures higher than 37 °C, in sodium borate RNA degradation begins at pH 7.0 and at 37 °C. RNA hydrolysis promoted under the combined catalytic activity of buffer/Mg2+ results in partially degraded RNA and negligible amounts of acid-soluble material. Reaction is insensitive to the concentration of monovalent cations but is completely prevented by chelating agents (EDTA and citrate) at concentrations exceeding that of Mg2+. Borate-magnesium reaction is inhibited also by some polyvalent alcohols (glycerol) and sugars.

Study on desorption of Mn, Fe, and Mg from TMP and evaluation of the complexing strength of different chelating agents using side reaction coefficients 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Holzforschung ◽  
2009 ◽  
Vol 63 (6) ◽  
Author(s):  
Kim Granholm ◽  
Pingping Su ◽  
Leo Harju ◽  
Ari Ivaska
Keyword(s):  
Citric Acid ◽  
Metal Ions ◽  
Chelating Agents ◽  
Side Reaction ◽  
Sodium Dithionite ◽  
Thermomechanical Pulp ◽  
Peroxide Bleaching ◽  
Ph Values ◽  
Reducing Environment ◽  
Ph Range

Abstract Chelation of thermomechanical pulp (TMP) was studied in this work. The desorption of Mn, Fe, and Mg due to their impact on peroxide bleaching was investigated. The desorption experiments were performed with EDTA, citric acid, oxalic acid, and formic acid as chelating agents at different pH. Chelation experiments with EDTA were carried out at pH 3–11. Sodium dithionite was used as the reducing agent in studying chelation with EDTA in a reducing environment. Mn was very effectively desorbed with EDTA from TMP at pH <10 and the reducing environment further improved the removal of all the studied metal ions from TMP with EDTA. Citric acid also removed Mn effectively from TMP at pH 5. The thermodynamic stability constants of different metal chelates do not present the correct picture of how strongly the metal ions are bound by the chelating agents in different conditions. But by means of the side reaction coefficients (α M(L)-coefficients) it is also theoretically possible to evaluate and compare the real binding strengths between the metal ions and different chelating agents at varying pH values and other solution conditions. In this study, a theory is given for the calculation of side reaction coefficients. Values of the α M(L)-coefficients, for the pH range 0–14, are presented for EDTA, DTPA, and also for some other new potential environmentally friendly chelating agents.

scholarly journals Efficient independent activity of a monomeric, monofunctional dehydroquinate synthase derived from the N-terminus of the pentafunctional AROM protein of Aspergillus nidulans

1994 ◽  
Vol 301 (1) ◽  
pp. 297-304 ◽  
Author(s):  
J D Moore ◽  
J R Coggins ◽  
R Virden ◽  
A R Hawkins
Keyword(s):  
Escherichia Coli ◽  
Catalytic Activity ◽  
Aspergillus Nidulans ◽  
Chelating Agents ◽  
Size Exclusion ◽  
Functional Domain ◽  
N Terminus ◽  
Exclusion Chromatography ◽  
Km Value ◽  
Dehydroquinate Synthase

The dehydroquinate synthase (DHQ synthase) functional domain from the pentafunctional AROM protein of Aspergillus nidulans has previously been overproduced in Escherichia coli [van den Hombergh, Moore, Charles and Hawkins (1992) Biochem J. 284, 861-867]. We now report the purification of this domain to homogeneity and subsequent characterization. The monofunctional DHQ synthase was found to retain efficient catalytic activity when compared with the intact pentafunctional AROM protein of Neurospora crassa [Lambert, Boocock and Coggins (1985) Biochem J. 226, 817-829]. The apparent kcat. was estimated to be 8 s-1, and the apparent Km values for NAD+ and 3-deoxy-D-arabino-heptulosonate phosphate (DAHP) were 3 microM and 2.2 microM respectively. These values are similar to those reported for the intact N. crassa enzyme, except that the apparent Km for NAD+ reported here is 15-fold higher. The monofunctional DHQ synthase domain is inactivated by treatment with chelating agents in the absence of substrates and is re-activated by the addition of metal ions; among those tested, Zn2+ gave the highest kcat./Km value. The enzyme is inactivated by diethyl pyrocarbonate; both the substrate, DAHP, and the product phosphate protected against inactivation. Size-exclusion chromatography suggested an M(r) of 43,000 for the monofunctional domain, indicating that it is monomeric and compactly folded. The c.d. spectrum confirmed that the domain has a compact globular conformation; the near-u.v. c.d. of zinc- and cobalt-reactivated domains were superimposable.

scholarly journals Activity and Surface Structure of Sulfided NiW/Al2O3 Catalyst: Effects of Chelating Agents on the Catalytic Activity for the Hydrogenation of Tetralin and o-Xylene

2004 ◽  
Vol 47 (4) ◽  
pp. 249-257 ◽  
Author(s):  
Hideyuki Itou ◽  
Naoto Koizumi ◽  
Naoko Sakamoto ◽  
Takehide Honma ◽  
Masahiro Shingu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Surface Structure ◽  
Chelating Agents

scholarly journals Sulphate-activated phosphorylase b: the pH-dependence of catalytic activity

1995 ◽  
Vol 310 (2) ◽  
pp. 565-570 ◽  
Author(s):  
S E Zographos ◽  
N G Oikonomakos ◽  
H B F Dixon ◽  
W G Griffin ◽  
L N Johnson ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Ammonium Sulphate ◽  
Ph Dependence ◽  
Glycogen Synthesis ◽  
Structural Data ◽  
Ph Optimum ◽  
Ph Values ◽  
Binary Complexes ◽  
Catalytic Constant ◽  
Bell Shaped Curve

The pH-dependence of sulphate-activated phosphorylase b has been studied in the direction of glycogen synthesis. The bell-shaped curve of the pH-dependence of the catalytic constant for the AMP-activated enzyme showed pK values of 6.1 and 7.3, but the curve for the enzyme activated by 0.9 M ammonium sulphate showed a drop of activity on the acid side at much higher pH values. Its bell was centred at pH 7.8 but it was too narrow to be characterized by only two pK values. The narrowness of the curve could be explained by positive co-operativity, but not its unusually steep acid side. We suggest that the fall on the acid side is due to more than one hydronation (addition of H+). The points can be fitted by a curve with two de-activating hydronations and a de-activating dehydronation having identical titration pK values of 7.5, and hence molecular values of 7.0, 7.5 and 8.0. If both 0.9 M ammonium sulphate and 5 mM AMP are added, the bell is as broad as with AMP alone, but is somewhat raised in pH optimum. The results are discussed in the light of new structural data from crystallographic studies on binary complexes of the enzyme.

scholarly journals Superoxide-dependent and ascorbate-dependent formation of hydroxyl radicals from hydrogen peroxide in the presence of iron. Are lactoferrin and transferrin promoters of hydroxyl-radical generation?

1987 ◽  
Vol 241 (1) ◽  
pp. 273-278 ◽  
Author(s):  
O I Aruoma ◽  
B Halliwell
Keyword(s):  
Hydroxyl Radical ◽  
Hydroxyl Radicals ◽  
Chelating Agents ◽  
Acidic Ph ◽  
Iron Ion ◽  
Ph Values ◽  
Protective Ability ◽  
Ferritin Iron ◽  
Radical Generation ◽  
Ionic Iron

Apo-lactoferrin and apo-transferrin protect against iron-ion-dependent hydroxyl-radical (.OH) generation from H2O2 in the presence of superoxide radicals or ascorbic acid at pH 7.4, whether the necessary iron is added as ionic iron or as ferritin. Iron-loaded transferrin and lactoferrin [2 mol of Fe(III)/mol] show no protective ability, but do not themselves accelerate .OH production unless chelating agents are present in the reaction mixture, especially if the proteins are incorrectly loaded with iron. At acidic pH values, the protective ability of the apoproteins is diminished, and the fully iron-loaded proteins can release some iron in a form able to accelerate .OH generation. The physiological significance of these observations is discussed.

Role of Molecular Structure of Complexing/Chelating Agents in Copper CMP Slurries

2005 ◽  
Vol 867 ◽  
Author(s):  
Udaya B. Patri ◽  
S. Pandija ◽  
S.V. Babu
Keyword(s):  
Molecular Structure ◽  
Functional Groups ◽  
Chelating Agents ◽  
Carbon Chain ◽  
Carbon Chain Length ◽  
Removal Rates ◽  
Ph Values ◽  
Amino Butyric Acid ◽  
Acidic Conditions

AbstractThe role of the molecular structure - different functional groups, the length of the carbon chain and the relative positions of different functional groups – of several complexing/chelating agents (acetic acid, glycine, ethylene diamine, succinic acid, alanine and amino butyric acid (ABA)) in controlling copper (Cu) removal rates was investigated. The results are consistent with the known activity of –COOH groups at acidic conditions and that of –NH2 groups in an alkaline environment. In comparison with glycine, it was also observed that an increase in the carbon chain length increased the removal rates at acidic pH values and decreased the removal rates at alkaline pH values. Also, Cu removal rates decreased with an increase in the distance between the –NH2 and –COOH groups in an amino acid at all pH values except at 4.

Rational design of porous binary Pt-based nanodendrites as efficient catalysts for direct glucose fuel cells over a wide pH range

2017 ◽  
Vol 7 (13) ◽  
pp. 2819-2827 ◽  
Author(s):  
Kamel Eid ◽  
Yahia H. Ahmad ◽  
Siham Y. AlQaradawi ◽  
Nageh K. Allam
Keyword(s):  
Catalytic Activity ◽  
Oxidation Reaction ◽  
Rational Design ◽  
Glucose Oxidation ◽  
Room Temperature ◽  
Ph Values ◽  
Wide Ph Range ◽  
One Step ◽  
Ph Range ◽  
Glucose Oxidation Reaction

Porous binary PtPd, AuPt, PtCu, and PtNi nanodendrites prepared by a facile one-step reduction under ultrasonic irradiation at room temperature, exhibited a substantial catalytic activity towards glucose oxidation reaction at different pH values relative to a commercial Pt/C catalyst.

scholarly journals Posttranscriptional gene silencing in nuclei

2010 ◽  
Vol 108 (1) ◽  
pp. 409-414 ◽  
Author(s):  
Paul Hoffer ◽  
Sergey Ivashuta ◽  
Olga Pontes ◽  
Alexa Vitins ◽  
Craig Pikaard ◽  
...  
Keyword(s):  
Gene Silencing ◽  
Target Genes ◽  
Rna Degradation ◽  
Small Interfering Rnas ◽  
Double Stranded Rna ◽  
Posttranscriptional Gene Silencing ◽  
Subcellular Compartmentation ◽  
Specific Degradation ◽  
Precursor Mrna ◽  
Specific Sequences

In plants, small interfering RNAs (siRNAs) with sequence homology to transcribed regions of genes can guide the sequence-specific degradation of corresponding mRNAs, leading to posttranscriptional gene silencing (PTGS). The current consensus is that siRNA-mediated PTGS occurs primarily in the cytoplasm where target mRNAs are localized and translated into proteins. However, expression of an inverted-repeat double-stranded RNA corresponding to the soybeanFAD2-1Adesaturase intron is sufficient to silenceFAD2-1, implicating nuclear precursor mRNA (pre-mRNA) rather than cytosolic mRNA as the target of PTGS. SilencingFAD2-1using intronic or 3′-UTR sequences does not affect transcription rates of the target genes but results in the strong reduction of target transcript levels in the nucleus. Moreover, siRNAs corresponding to pre-mRNA–specific sequences accumulate in the nucleus. In Arabidopsis, we find that two enzymes involved in PTGS, Dicer-like 4 and RNA-dependent RNA polymerase 6, are localized in the nucleus. Collectively, these results demonstrate that siRNA-directed RNA degradation can take place in the nucleus, suggesting the need for a more complex view of the subcellular compartmentation of PTGS in plants.

Structural and Adsorption Effects of Some Thiopurine and Thiopyrimidine Derivatives on their Catalytic Activity at the Mercury Electrode

1994 ◽  
Vol 59 (7) ◽  
pp. 1472-1482 ◽  
Author(s):  
Mohamed Sayed Ibrahim
Keyword(s):  
Catalytic Activity ◽  
Catalytic Effect ◽  
Mercury Electrode ◽  
Surface Characteristics ◽  
Reduction Wave ◽  
Ph Values ◽  
Catalytic Wave ◽  
Dc Polarography ◽  
Catalytic Hydrogen ◽  
Catalytic Hydrogen Evolution

6-Thiopurine, 6-thiopurine riboside, 6-thioguanine, 6-thioguanosine, 8-thioguanosine, 2-thiouracil, 4-thiouridine, 2-thiocytosine and 2-thiocytidine are investigated by means of DC polarography and coulometry. In acid medium they give a typical catalytic hydrogen discharge wave, as shown by its parameters and the regeneration of the depolarizer during the electrode process. At pH values above 4.2 a second catalytic wave appears. Both catalytic waves possess pronounced surface characteristics, most likely due to adsorption of the molecules with differing orientations on the electrode surface. The catalytic wave overlaps the reduction wave, which is placed in evidence under conditions where the catalytic effect is absent. Under the same conditions, 2-thiouracil was found to be catalytically inactive, but it induces catalytic hydrogen evolution in Co(II)-containing ammonia buffer. The present results indicate that the position of thio group yields also such distinct change in the catalytic activity of the investigated compounds.

Modulating the surface segregation of PdCuRu nanocrystals for enhanced all-pH hydrogen evolution electrocatalysis

2019 ◽  
Vol 7 (35) ◽  
pp. 20151-20157 ◽  
Author(s):  
Menggang Li ◽  
Mingchuan Luo ◽  
Zhonghong Xia ◽  
Yong Yang ◽  
Yarong Huang ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Hydrogen Evolution ◽  
High Performance ◽  
Surface Segregation ◽  
Core Shell ◽  
Ph Values

Core–shell PdCuRu trimetallic nanocrystals with a Pd-rich shell can be obtained by leveraging controlled surface segregation, and high-performance HER catalytic activity finally was achieved at all pH values.

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