scholarly journals pH-jump studies at subzero temperatures on an intermediate in the reaction of xanthine oxidase with xanthine

1978 ◽  
Vol 175 (3) ◽  
pp. 879-885 ◽  
Author(s):  
A D Tsopanakis ◽  
S J Tanner ◽  
R C Bray
Keyword(s):  
Nitrate Reductase ◽  
Xanthine Oxidase ◽  
Low Ph ◽  
High Ph ◽  
Ph Values ◽  
Exchangeable Proton ◽  
Subzero Temperatures ◽  
Ph Jump ◽  
Unique Nature ◽  
Prototropic Equilibrium

Xanthine oxidase is stable and active in aqueous dimethyl sulphoxide solutions of up to at least 57% (w/w). Simple techniques are described for mixing the enzyme in this solvent at–82 degrees C, with its substrate, xanthine. When working at high pH values under such conditions, no reaction occurred, as judged by the absence of e.p.r. signals. On warming to–60 degrees C, for 10 min, however, the Very Rapid molybdenum(V) e.p.r. signal was obtained. This signal did not change on decreasing the pH, while maintaining the sample in liquid nitrate reductase, caused its molybdenum(V) e.p.r. signal to change from the high-pH to the low-pH form. These findings are not compatible with the conclusions of Edmondson, Ballou, Van Heuvelen, Palmer & Massey [J. Biol. Chem. (1973) 248, 6135-6144], that the Very Rapid signal is in prototropic equilibrium with the Rapid signal, and should be important in understanding the mechanism of action of the enzyme. They emphasize the unique nature of the intermediate represented by the Very Rapid e.p.r. signal. The possible value of the pK for loss of an exchangeable proton from the Rapid signal is discussed.

scholarly journals Electron-paramagnetic-resonance studies on nitrate reductase from Escherichia coli K12

1978 ◽  
Vol 171 (3) ◽  
pp. 639-647 ◽  
Author(s):  
Stephen P. Vincent ◽  
Robert C. Bray
Keyword(s):  
Escherichia Coli ◽  
Nitrate Reductase ◽  
Extraction Procedure ◽  
Hydrophobic Interaction Chromatography ◽  
Low Ph ◽  
Paramagnetic Resonance ◽  
Escherichia Coli K12 ◽  
Exchangeable Proton ◽  
Ph Range ◽  
Nitrate And Nitrite

Nitrate reductase was purified from anaerobically grown Escherichia coli K12 by a method based on the Triton X-100 extraction procedure of Clegg[(1976) Biochem. J.153, 533–541], but hydrophobic interaction chromatography was used in the final stage. E.p.r. spectra obtained from the enzyme under a variety of conditions are well resolved and were interpreted with the help of the computer-simulation procedures of Lowe [(1978) Biochem. J.171, 649–651]. Parameters for five molybdenum(V) species from the enzyme are given. The low-pH species (gav. 1.9827) is in pH-dependent equilibrium with the high-pH species (gav. 1.9762), the pK for interconversion of the species being 8.26. Of a variety of anions tested, only nitrate and nitrite formed complexes with the enzyme (in the low-pH form), giving modified molybdenum(V) e.p.r. spectra. These complexes, as well as the low-pH form of the free enzyme, showed interaction of molybdenum with a single exchangeable proton. The fifth molybdenum(V) species, sometimes detected in small amounts, appears not to be due to functional nitrate reductase. After full reduction of the enzyme with dithionite, addition of nitrate caused reoxidation of molybdenum to the quinquivalent state, in a time less than the enzyme turnover. Activity of the enzyme in the pH range 6–10 is controlled by a pK of 8.2. It is suggested that the low-pH signal-giving species is the form of the enzyme involved in the catalytic cycle. Iron–sulphur and other e.p.r. signals from the enzyme are briefly described and the enzymic reaction mechanism is discussed.

Hydrothermal crystallization kinetics of m-ZrO2 and t-ZrO2

1990 ◽  
Vol 5 (11) ◽  
pp. 2698-2705 ◽  
Author(s):  
Raymond P. Denkewicz ◽  
Kevor S. TenHuisen ◽  
James H. Adair
Keyword(s):  
Crystallization Kinetics ◽  
Low Ph ◽  
Formation Mechanisms ◽  
Gel Structure ◽  
Hydrothermal Conditions ◽  
High Ph ◽  
Ph Values ◽  
Ph Conditions ◽  
Apparent Activation Energies ◽  
Kinetics Of

The isothermal nucleation and crystallization kinetics of hydrothermally prepared monoclinic and tetragonal ZrO2 have been determined at various pH conditions. It is shown that monoclinic ZrO2 precipitates at low pH whereas at high pH tetragonal ZrO2 crystallizes from an amorphous zirconium (hydrous) oxide, Zr(OH)xOy, precursor. At intermediate pH conditions mixtures of the polymorphs are formed suggestive of kinetically competing particle formation mechanisms. The data are explained by the proposed existence of three controlling regimes for the formation of crystalline ZrO2: dissolution/precipitation at low pH, a solubility controlled regime at intermediate pH values, and a gel structure controlled regime at high pH. Apparent activation energies for the nucleation and crystallization of monoclinic and tetragonal ZrO2 formed under hydrothermal conditions are presented.

Electronic and Raman spectroscopic studies of copper adrenalin complexes and copper induced compounds

1976 ◽  
Vol 54 (24) ◽  
pp. 3815-3823 ◽  
Author(s):  
Mohammed S. Rahaman ◽  
Stephen M. Korenkiewicz
Keyword(s):  
Free Radical ◽  
Hydrochloric Acid ◽  
Raman Spectra ◽  
Spectroscopic Studies ◽  
Low Ph ◽  
Basic Solution ◽  
High Ph ◽  
Raman Spectroscopic ◽  
Ph Values

Electronic and Raman spectra of adrenalin–copper(II) complexes and copper catalyzed compounds have been studied. Adrenalin reacts with copper(II) ion at pH 9.2 and higher to produce a very short lived violet free radical, a brown adrenochrome, a yellow conjugated salt, indolyl-indoquinone, and melanin. Results indicate that copper does not form complexes with adrenalin in basic solution. Between pH 6.5 and 8.5 adrenalin transforms into adrenochrome in presence of copper. The adrenochrome in 1.5 N hydrochloric acid produces the conjugate salt that is produced in the solution of high pH. At low pH values, between pH 4.0 to 5.5, adrenalin forms a brown complex with copper(II). Copper is entirely chelated to the phenolic groups of the amines. The complex in 1.5 N hydrochloric acid produces a black polymeric pigment.

scholarly journals The mechanism of action of xanthine oxidase. The relationship between the rapid and very rapid molybdenum electron-paramagnetic-resonance signals

1979 ◽  
Vol 177 (1) ◽  
pp. 357-360 ◽  
Author(s):  
R C Bray ◽  
S Gutteridge ◽  
D A Stotter ◽  
S J Tanner
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Xanthine Oxidase ◽  
Low Ph ◽  
Active Centre ◽  
Paramagnetic Resonance ◽  
Alternative Pathways ◽  
Ph Values ◽  
Covalent Intermediate ◽  
The Relationship ◽  
Electron Paramagnetic

On the basis of the work of Gutteridge, Tanner & Bray [Biochem. J. (1978) 175, 887-897] and of other data in the literature, a mechanism for the reaction of xanthine oxidase with reducing substrates is proposed. In the Michaelis complex, xanthine is bound to molybdenum via the N-9 nitrogen atom. Coupled transfer of two electrons to molybdenum and the C-8 proton to the enzyme yields (Enzyme)-Mo-SH. Concerted with this process, reaction of the xanthine residue with a nucleophile in the active centre yields a covalent intermediate that breaks down to give the product by alternative pathways at high and at low pH values.

scholarly journals pH Tolerance in Freshwater Bacterioplankton: Trait Variation of the Community as Measured by Leucine Incorporation

2015 ◽  
Vol 81 (21) ◽  
pp. 7411-7419 ◽  
Author(s):  
Erland Bååth ◽  
Emma Kritzberg
Keyword(s):  
Bacterial Growth ◽  
Low Ph ◽  
Tolerance Index ◽  
Response Curves ◽  
Trait Variation ◽  
High Ph ◽  
Ph Values ◽  
Ph Tolerance ◽  
Community Tolerance

ABSTRACTpH is an important factor determining bacterial community composition in soil and water. We have directly determined the community tolerance (trait variation) to pH in communities from 22 lakes and streams ranging in pH from 4 to 9 using a growth-based method not relying on distinguishing between individual populations. The pH in the water samples was altered to up to 16 pH values, coveringin situpH ± 2.5 U, and the tolerance was assessed by measuring bacterial growth (Leu incorporation) instantaneously after pH adjustment. The resulting unimodal response curves, reflecting community tolerance to pH, were well modeled with a double logistic equation (meanR2= 0.97). The optimal pH for growth (pHopt) among the bacterial communities was closely correlated within situpH, with a slope (0.89 ± 0.099) close to unity. The pH interval, in which growth was ≥90% of that at pHopt, was 1.1 to 3 pH units wide (mean 2.0 pH units). Tolerance response curves of communities originating from circum-neutral pH were symmetrical, whereas in high-pH (8.9) and especially in low-pH (<5.5) waters, asymmetric tolerance curves were found. In low-pH waters, decreasing pH was more detrimental for bacterial growth than increasing pH, with a tendency for the opposite for high-pH waters. A pH tolerance index, using the ratio of growth at only two pH values (pH 4 and 8), was closely related to pHopt(R2= 0.83), allowing for easy determination of pH tolerance during rapid changes in pH.

Effects of pH on Hg0 Re-Emission in WFGD

2014 ◽  
Vol 960-961 ◽  
pp. 462-468 ◽  
Author(s):  
Yong Qiu ◽  
Hui Wu ◽  
Guang Qian Luo ◽  
Hong Yao
Keyword(s):  
Flue Gas ◽  
Laboratory Experiments ◽  
Low Ph ◽  
Time Span ◽  
Flue Gas Desulfurization ◽  
Solution Theory ◽  
High Ph ◽  
Ph Values ◽  
Effects Of Ph ◽  
Conventional Solution

Gaseous oxidized mercury (Hg2+) in the flue gas is soluble in water and can be captured effectively by Wet flue gas desulfurization (WFGD) system. But in some extent Hg0re-emission happens due to the reduction of absorbed Hg2+, and the pH of slurry is an important factor affecting Hg0re-emission. In this study, the theoretical formulas of slurry pH were derived through the conventional solution theory and then were used to evaluate the factors determining the pH of slurry. A series of laboratory experiments were carried out under N2,CO2and O2/N2atmosphere to measure the Hg0re-emission tendency at different pH values. The results show that the higher the pH, the less Hg2+reduced by S(IV), resulting in the decrease of Hg0re-emission. Under N2atmosphere, the Hg0re-emission was mild at pH>4 while it was dramatic at pH<4. Under O2/N2atmosphere, the addition of O2extended the time span of Hg0re-emission at low pH and increased Hg0re-emission unexpectedly in the latter part of the experiments at high pH. CO2atmosphere almost did not affect Hg0re-emission because of its little effect on the slurry pH.

scholarly journals Structural Changes of Co Caused a Change of the Solution pH During Chemical Deposition

2020 ◽  
pp. 451-458
Author(s):  
Sergey A. Podorozhnyak ◽  
Anatoly V. Chzhan ◽  
Vadim K. Maltsev ◽  
Ivan N. Krayuhin ◽  
Gennady S. Patrin ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Crystal Lattice ◽  
Phase Transformations ◽  
Structural Changes ◽  
Chemical Deposition ◽  
Low Ph ◽  
Nanocrystalline State ◽  
Solution Ph ◽  
High Ph ◽  
Ph Values

The phase transformations of the Co lattice are discussed, which determine the anomalous changes in the magnetic properties of chemically deposited Co-P films obtained at various pH values. The coercivity of the Hc films obtained at low pH values exceeds 1 kOe and decreases to several units Oe in the films obtained at high pH values. It is shown that the observed changes in the magnetic properties of Co-P films are caused by the transition of the cobalt crystal lattice to the nanocrystalline state

THE EFFECT OF NITROGEN AND PHOSPHORUS NUTRITION ON pH OF TOMATO

1966 ◽  
Vol 46 (6) ◽  
pp. 681-684 ◽  
Author(s):  
J. S. Matthews ◽  
L. G. Denby
Keyword(s):  
Low Ph ◽  
The Other ◽  
Phosphorus Nutrition ◽  
Nitrogen And Phosphorus ◽  
Tomato Fruits ◽  
High Ph ◽  
Ph Values ◽  
Low Levels ◽  
Nutrient Solutions

Tomato fruits, grown under glass in inert media, and supplied with nutrient solutions containing high and low levels of N and P, varied in pH from 4.21 to 4.61. Fruits from plants receiving low levels of both nutrients consistently had low pH values. Those from plants fed high levels of P or N had high pH whenever the level of the other element was not limiting.

scholarly journals Complexes with halide and other anions of the molybdenum centre of nitrate reductase from Escherichia coli

1985 ◽  
Vol 227 (3) ◽  
pp. 925-931 ◽  
Author(s):  
G N George ◽  
R C Bray ◽  
F F Morpeth ◽  
D H Boxer
Keyword(s):  
Escherichia Coli ◽  
Nitrate Reductase ◽  
Strong Coupling ◽  
Low Ph ◽  
High Ph ◽  
Single Proton

The interconversion of nitrate reductase from Escherichia coli between low-pH and high-pH Mo(V) e.p.r. signal-giving species was re-investigated [cf. Vincent & Bray (1978) Biochem. J. 171, 639-647]. The process cannot be described by a single pK value, since the apparent pK for interconversion is raised by the presence of various anions. The low-pH form of the enzyme exists as a series of complexes with different anion ligands of molybdenum. Each complex has specific and slightly different e.p.r. parameters, but all show strong coupling of Mo(V) to a single proton, exchangeable with the solvent, having A(1H)av. 1.0 to 1.3 mT. Complexes with Cl-, F- [A(19F)av. 0.7 mT], NO3- and NO2- give particularly well-defined spectra. The high-pH form of the enzyme is now shown to bear a coupled proton. Like that in the low-pH species, this proton is exchangeable with the solvent, but the coupling is much weaker, with A(1H)av. 0.3 mT. Thus, contrary to earlier assumptions, the proton detectable by e.p.r. is probably not identical with the proton whose dissociation controls interconversion between the two species; the latter proton could be located in the protein rather than on a ligand of molybdenum. Treatment of the enzyme with trypsin [Morpeth & Boxer (1985) Biochemistry 24, 40-46] did not affect its Mo(V) e.p.r. signals.

Comparative Study of p-nitrophenyl picolinate Hydrolysis Catalyzed by Bis(O,O’-di(2-phenylalkyl)dithiophosphate) nickel(II)

2012 ◽  
Vol 560-561 ◽  
pp. 305-308 ◽  
Author(s):  
Bing Ying Jiang ◽  
Fa Mei Feng ◽  
Min Wang ◽  
Ci Li ◽  
Jia Qing Xie
Keyword(s):  
Comparative Study ◽  
Metal Complexes ◽  
Low Ph ◽  
Nucleophilic Attack ◽  
High Ph ◽  
Ph Values ◽  
Catalytic Function ◽  
Hydrolysis Of ◽  
Pnpp Hydrolysis ◽  
Synergism Effect

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by two nickel (II) complexes (bis(O,O’-di(2-phenylmethyl) dithiophosphate) nickel(II) (NiR1) and bis(O,O’-di(2-phenylethyl) dithiophosphate) nickel(II) (NiR2)) was investigated kinetically in this work. The results indicate that both metal complexes accelerate the hydrolysis of PNPP dramatically and the NiR1 exhibits higher catalytic function on PNPP hydrolysis in the buffered solution with relatively low pH values, while NiR2 shows slightly more efficacy on hydrolysis of PNPP in relatively high pH buffered solutions. This variance is ascribed to the synergism effect of space hindrance of the complexes and the nucleophilic attack of metal-hydroxy species generated by the complexes.

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