scholarly journals Pyruvatephosphate dikinase from Bacteroides symbiosus

1971 ◽  
Vol 125 (2) ◽  
pp. 531-539 ◽  
Author(s):  
Richard E. Reeves
Keyword(s):  
Metal Ion ◽  
Adenine Nucleotides ◽  
Thiol Compounds ◽  
Pyruvate Phosphate Dikinase ◽  
Constant Ph ◽  
Bacterial Enzyme ◽  
Rate Of Reaction ◽  
Ph Stat ◽  
Magnesium Salts ◽  
Nucleotide Specificity

1. An improved method is given for preparation of pyruvate, phosphate dikinase from Bacteroides symbiosus. 2. The bacterial enzyme is stable, free from interfering enzyme activities, and does not require thiol compounds to maintain stability during storage or assay. 3. New direct assays of enzyme activity are based on acid evolution or consumption as measured at constant pH in a pH-stat. 4. The optimum rate of reaction in the direction of pyruvate formation occurs at about pH6.4; in the direction of phosphoenolpyruvate formation, it is at pH7.2–7.8. 5. Newly determined substrate Km values for the enzyme are: AMP, 3.5×10−6m; ATP, 1×10−4m; pyruvate, 8×10−5m; Pi, 6×10−4m. 6. K+ may substitute for NH4+ in activating the reaction catalysed by the B. symbiosus enzyme. 7. In the direction of pyruvate formation the bivalent metal ion requirement of the enzyme is fulfilled by salts of nickel, manganese, magnesium and cobalt. In the other direction only magnesium salts were effective. 8. The nucleotide specificity of the enzyme is strictly limited to the adenine nucleotides. CTP and ITP strongly inhibit the reaction in the direction of phosphoenolpyruvate formation.

scholarly journals Purification and properties of α-d-mannosidase from the limpet, Patella vulgata

1970 ◽  
Vol 117 (1) ◽  
pp. 129-137 ◽  
Author(s):  
Sybil M. Snaith ◽  
G. A. Levvy ◽  
A. J. Hay
Keyword(s):  
Metal Ion ◽  
Reversible Inactivation ◽  
Patella Vulgata ◽  
Full Activity ◽  
Acid Ph ◽  
Purification And Properties ◽  
Rate Of Reaction ◽  
Metal Ion Complex

1. α-Mannosidase from the limpet, Patella vulgata, was purified nearly 150-fold, with 40% recovery. β-N-Acetylglucosaminidase was removed from the preparation by treatment with ethanol. The final product was virtually free from β-galactosidase. 2. Limpet α-mannosidase was assayed at pH3.5 and at this pH it was necessary to add Zn2+ for full activity. At pH5, the enzyme had the same activity in the presence or absence of added Zn2+. 3. On incubation at acid pH, the enzyme underwent reversible inactivation, which was prevented by adding Zn2+. 4. EDTA accelerated inactivation and the addition of Zn2+ at once restored activity. No other cation was found to reactivate the enzyme. 5. Cl- had an unspecific effect on hydrolysis by limpet α-mannosidase. It increased the rate of reaction with substrate. The anion did not prevent or reverse inactivation by EDTA. 6. It is concluded that α-mannosidase is a metalloenzyme or enzyme–metal ion complex, dissociable at the pH of activity, and that it requires Zn2+ specifically.

Review article : Acid-base status, hypothermia and cardiac surgery

Perfusion ◽  
1986 ◽  
Vol 1 (4) ◽  
pp. 231-238 ◽  
Author(s):  
Julie A Swain
Keyword(s):  
Cardiac Surgery ◽  
Review Article ◽  
Acid Base ◽  
Optimal Method ◽  
Management Scheme ◽  
Constant Ph ◽  
Acid Base Status ◽  
Laboratory Investigations ◽  
Ph Stat ◽  
Ph Management

The optimal method of pH management during hypothermia is controversial. A review of current experimental and laboratory investigations comparing different pH schemes is presented. The biochemical and metabolic consequences of keeping pH constant (pH-stat) as compared to allowing the pH to increase with hypothermia (alpha-stat) are discussed. It is concluded that, on the basis of experimental and clinical studies, the alpha-stat pH management scheme may be preferable to that of keeping pH constant throughout a wide temperature range in humans.

scholarly journals Precipitation of Inorganic Salts in Mitochondrial Matrix

Membranes ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 81
Author(s):  
Jerzy J. Jasielec ◽  
Robert Filipek ◽  
Krzysztof Dołowy ◽  
Andrzej Lewenstam
Keyword(s):  
Calcium Concentration ◽  
Mitochondrial Matrix ◽  
Irreversible Damage ◽  
Atp Production ◽  
Physiological Conditions ◽  
Carbonated Apatite ◽  
Constant Ph ◽  
The Matrix ◽  
Magnesium Salts ◽  
Ph Buffer

In the mitochondrial matrix, there are insoluble, osmotically inactive complexes that maintain a constant pH and calcium concentration. In the present paper, we examine the properties of insoluble calcium and magnesium salts, such as phosphates, carbonates and polyphosphates, which might play this role. We find that non-stoichiometric, magnesium-rich carbonated apatite, with very low crystallinity, precipitates in the matrix under physiological conditions. Precipitated salt acts as pH buffer, and, hence, can contribute in maintaining ATP production in ischemic conditions, which delays irreversible damage to heart and brain cells after stroke.

Sorption of Heavy Metal on Natural Clay

2018 ◽  
Vol 68 (12) ◽  
pp. 2804-2807
Author(s):  
Mircea Stefan ◽  
Adriana Bors ◽  
Daniela Simina Stefan ◽  
Ionut Alexandru Savu Radu ◽  
Cicerone Marinescu
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Metal Ion ◽  
Background Electrolyte ◽  
Hydroxyl Groups ◽  
Natural Clay ◽  
Equilibrium Isotherms ◽  
Solution Ph ◽  
Constant Ph ◽  
Langmuir Isotherm Model

Sorption of heavy metals on Na-montmorillonite was studied as a function of solution pH and different concentrations of background electrolyte and also a function of added metal ion at constant pH. Equilibrium isotherms have been measured and analyzed using a Langmuir isotherm model. The metal ions were predominantly adsorbed on the permanent charge sites in a easily replaceable state. There was also evident a substantial involvement of the hydroxyl groups on the edges of Na-montmorillonite in specific adsorption of the cations especially at higher pH.

Coupling pH-stat and DO-stat titration to monitor degradation of organic substrates

2004 ◽  
Vol 49 (1) ◽  
pp. 69-77 ◽  
Author(s):  
E. Ficara ◽  
A. Rozzi
Keyword(s):  
Oxygen Uptake Rate ◽  
Treatment Plant ◽  
Domestic Wastewater ◽  
Organic Substrates ◽  
Dissolved Oxygen Concentration ◽  
Carbon Dioxide Evolution ◽  
Constant Ph ◽  
Domestic Wastewater Treatment ◽  
Carbon Dioxide Evolution Rate ◽  
Ph Stat

A combined titration methodology at constant pH and dissolved oxygen concentration to monitor the degradation of organics as carbon dioxide evolution rate (CER) and oxygen uptake rate (OUR) is presented. Equations necessary to assess CER from alkali titration rates and the instrument used to test the technique are described. Experiments were performed on samples of activated sludge from a domestic wastewater treatment plant using glucose and ethanol as substrates. OUR and CER were calculated for both substrates, as well as the respiratory quotient RQ = CER/OUR and biomass to substrate yields coefficients. RQ data for ethanol compared better with corresponding stoichiometric values than those for glucose.

scholarly journals Kinetics and Mechanism of Catalyzed Oxidation of L-Cysteine by Salen Schiff Base Complexes of Co(III), Fe (III) and Cr(III)

2021 ◽  
Vol 13 (2) ◽  
pp. 25
Author(s):  
Hamzeh M. Abdel-Halim ◽  
Hutaf M. Baker ◽  
Akef I. Alhmaideen ◽  
Adnan S. Abu-Surrah
Keyword(s):  
Schiff Base ◽  
Metal Ion ◽  
Reduction Potential ◽  
Order Conditions ◽  
Schiff Base Complexes ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Constant Ph ◽  
Kinetics Of ◽  
Catalyzed Oxidation

Kinetics of oxidation of L-cysteine by new series of substituted ONNO-donor salen-type Schiff base complexes of general formula [MIII(L)Cl] (M = Co, Fe, Cr; L = Schiff base ligand) have been studied in aqueous solutions. Measurements were run at constant temperature (25º C), constant ionic strength (0.20 M), and constant pH (7.0) under pseudo-first order conditions, in which the concentration of cysteine is around two orders of magnitude greater than that of metal complex. The observed rate constant was determined by following the change in absorbance of reaction mixture at a predetermined wavelength with time. Results show that the rate of oxidation depends on the type of metal center, with Co(III) complexes were found to have the highest rates due to higher reduction potential of Co(III). The oxidation rate was also found to depend on steric factor and the electron withdrawing / releasing ability of the ligand bound to the metal ion.

scholarly journals Kinetic and thermodynamic analysis defines roles for two metal ions in DNA polymerase specificity and catalysis

2020 ◽  
pp. jbc.RA120.016489
Author(s):  
Shanzhong Gong ◽  
Serdal Kirmizialtin ◽  
Adrienne Chang ◽  
Joshua E. Mayfield ◽  
Yan Jessie Zhang ◽  
...  
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Dna Polymerases ◽  
Critical Role ◽  
Md Simulations ◽  
Enzyme Analysis ◽  
Hiv Reverse Transcriptase ◽  
Nucleotide Incorporation ◽  
Weak Binding ◽  
Nucleotide Specificity

Magnesium ions play a critical role in catalysis by many enzymes and they contribute to the fidelity of DNA polymerases through a two-metal ion mechanism. However, specificity is a kinetic phenomenon and the roles of Mg2+ions in each step in catalysis have not been resolved. We first examined the roles of Mg2+ by kinetic analysis of single nucleotide incorporation catalyzed by HIV reverse transcriptase We show that Mg.dNTP binding induces an enzyme conformational change at a rate that is independent of free Mg2+ concentration. Subsequently, the second Mg2+ binds to the closed state of the enzyme-DNA-Mg.dNTP complex (Kd = 3.7 mM) to facilitate catalysis. Weak binding of the catalytic Mg2+ contributes to fidelity by sampling the correctly aligned substrate without perturbing the equilibrium for nucleotide binding at physiological Mg2+ concentrations. Increasing Mg2+ concentration from 0.25 to 10 mM increases nucleotide specificity (kcat/Km) 12-fold by largely increasing the rate of the chemistry relative to the rate of nucleotide release. Mg2+ binds very weakly (Kd ≤ 37 mM) to the open state of the enzyme. Analysis of published crystal structures showed that HIV RT binds only two metal ions prior to incorporation of a correct base-pair. MD simulations support the two-metal ion mechanism and the kinetic data indicating weak binding of the catalytic Mg2+. MD simulations also revealed the importance of the divalent cation cloud surrounding exposed phosphates on the DNA. These results enlighten the roles of the two metal ions the specificity of DNA polymerases.

scholarly journals Lipid peroxide formation in microsomes. The role of non-haem iron

1969 ◽  
Vol 113 (2) ◽  
pp. 325-332 ◽  
Author(s):  
E. D. Wills
Keyword(s):  
Metal Ion ◽  
Chelating Agents ◽  
Adenine Nucleotides ◽  
Liver Microsomes ◽  
Lipid Peroxide ◽  
Rat Liver Microsomes ◽  
Peroxide Formation ◽  
Haem Iron ◽  
Lipid Peroxide Formation

1. Metal ion-chelating agents such as EDTA, o-phenanthroline or desferrioxamine inhibit lipid peroxide formation when rat liver microsomes prepared from homogenates made in pure sucrose are incubated with ascorbate or NADPH. 2. Microsomes treated with metal ion-chelating agents do not form peroxide on incubation unless inorganic iron (Fe2+ or Fe3+) in a low concentration is added subsequently. No other metal ion can replace inorganic iron adequately. 3. Microsomes prepared from sucrose homogenates containing EDTA (1mm) do not form lipid peroxide on incubation with ascorbate or NADPH unless Fe2+ is added. Washing the microsomes with sucrose after preparation restores most of the capacity to form lipid peroxide. 4. Lipid peroxide formation in microsomes prepared from sucrose is stimulated to a small extent by inorganic iron but to a greater extent if adenine nucleotides, containing iron compounds as a contaminant, are added. 5. The iron contained in normal microsome preparations exists in haem and in non-haem forms. One non-haem component in which the iron may be linked to phosphate is considered to be essential for both the ascorbate system and NADPH system that catalyse lipid peroxidation in microsomes.

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