scholarly journals Properties of halophil nicotinamide–adenine dinucleotide phosphate-specific isocitrate dehydrogenase. True Michaelis constants, reaction mechanisms and molecular weights

1972 ◽  
Vol 130 (3) ◽  
pp. 645-662 ◽  
Author(s):  
D. M. Aitken ◽  
A. D. Brown
Keyword(s):  
Reaction Mechanism ◽  
Sodium Chloride ◽  
Potassium Chloride ◽  
Salt Concentration ◽  
Isocitrate Dehydrogenase ◽  
Reaction Mechanisms ◽  
Substrate Concentration ◽  
Gel Filtration ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Michaelis Constants

True values of Michaelis constants of the NADP+-specific isocitrate dehydrogenase from Halobacterium salinarium were not very different from those of the apparent constants reported by Aitken et al. (1970). The true constants were affected by salt in a similar manner to that of the apparent constants obtained with NADP+ at fixed concentrations of 1.0–0.2mm and threo-ds-(+)-isocitrate at fixed concentrations of 2.0–0.125mm. The response of apparent Vmax. to salt concentration was highly dependent on fixed substrate concentration in solutions of sodium chloride but much less so in solutions of potassium chloride. At several levels the results emphasize the difficulty of generalizing about the salt relations of a halophil enzyme without adequate attention to substrate concentration. The enzyme has at least two different reaction mechanisms depending on salt concentration. In its ‘physiological’ form (i.e. in 1.0m-potassium chloride), and also in 1.0m-sodium chloride, the reaction mechanism is ordered with NADP+ the first substrate added and NADPH the last product released. In 0.25m-sodium chloride, however, the mechanism is different and is probably non-sequential. In 4.0m-sodium chloride with low concentrations of either fixed substrate, there was evidence of a co-operative action of the variable substrate. The evidence suggests that salt participates in the reaction mechanism in two ways: one is the reversible addition to the enzyme in a manner analogous to that of a substrate; the other is dead-end complex-formation. The relative contributions of these two types of reaction determine whether salt activates or inhibits the enzyme. In addition, the inhibition caused by high concentrations of sodium chloride is more complex than the corresponding inhibition by potassium chloride. Gel-filtration experiments indicated that at very low salt concentrations the enzyme has an apparent molecular weight of about 70800. In ‘physiological’ concentrations of potassium chloride the enzyme appears to be a dimer (mol.wt. 122000–135000) and, in 1.0–4.0m-sodium chloride, it behaves as a trimer or tetramer (mol.wt. 224000–251000). A preliminary method of purifying the enzyme is described.

scholarly journals Properties of a halophil nicotinamide–adenine dinucleotide phosphate-specific isocitrate dehydrogenase. Preliminary studies of the salt relations and kinetics of the crude enzyme

1970 ◽  
Vol 116 (1) ◽  
pp. 125-134 ◽  
Author(s):  
D. M. Aitken ◽  
A. J. Wicken ◽  
A. D. Brown
Keyword(s):  
Sodium Chloride ◽  
Potassium Chloride ◽  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Competitive Inhibitor ◽  
Michaelis Constants ◽  
The Hill ◽  
Kinetics Of ◽  
Pronounced Inhibition

The effects of chlorides on NADP-specific isocitrate dehydrogenase from Halobacterium salinarium were investigated. The enzyme is stabilized by potassium chloride and sodium chloride and this effect is discussed in relation to the Hill (1913) equation. Kinetics of the enzyme were studied within a range of concentrations of potassium chloride and sodium chloride. Apparent Michaelis constants for both substrates were affected by salt concentration, the effect being greater in sodium chloride than in potassium chloride. Minimal apparent Michaelis constants for both substrates were similar to the corresponding constants reported for yeast isocitrate dehydrogenase. Vmax. was maximal in each salt at a concentration of about 1m. The maximum was higher in sodium chloride than in potassium chloride. At salt concentrations above about 2.3m, the apparent Vmax. was lower in sodium chloride than in potassium chloride, and at salt concentrations below 0.75–1.0m, each salt behaved as a linear activator of the enzyme. Within this concentration range salt and NADP+ acted competitively; the activation by salt was overcome at finite concentrations of NADP+. At concentrations above about 1m, potassium chloride was a linear non-competitive inhibitor of the enzyme. Within the range 1.0–2.5m, sodium chloride was also a linear non-competitive inhibitor, but above 2.5m it caused more pronounced inhibition.

THE GLYCEROL DEHYDROGENASES OF PSEUDOMONAS SALINARIA, VIBRIO COSTICOLUS, AND ESCHERICHIA COLI IN RELATION TO BACTERIAL HALOPHILISM

1954 ◽  
Vol 32 (1) ◽  
pp. 206-217 ◽  
Author(s):  
R. M. Baxter ◽  
N. E. Gibbons
Keyword(s):  
Escherichia Coli ◽  
Sodium Chloride ◽  
Potassium Chloride ◽  
Salt Concentration ◽  
Halophilic Bacteria ◽  
Molar Concentration ◽  
Moderately Halophilic ◽  
E Coli ◽  
High Concentrations ◽  
Chloride Concentrations

Glycerol dehydrogenases from the extremely halophilic Pseudomonas salinaria and the moderately halophilic Vibrio costicolus are described and compared with the corresponding enzyme from the nonhalophilic Escherichia coli. The properties of all three enzymes are similar except their responses to salt concentration. The enzymes from E. coli and V. costicolus are most active at sodium chloride concentrations of about 0.25 M and 0.5 M respectively; that from P. salinaria is not only most active in the presence of 1.5 M NaCl but is irreversibly inactivated in the absence of salt. All three enzymes are more active in the presence of potassium chloride than of sodium chloride at any given molar concentration. These results suggest that the extremely halophilic bacteria contain high concentrations of salt and that their enzymes function maximally at these high concentrations. In contrast the moderately halophilic organisms contain relatively little salt and their enzymes are more comparable with those of nonhalophiles.

Effect of Sodium Chloride and Potassium Chloride on Growth Response of Yeasts Saccharomyces uvarum and Kloeckera brevis to Free Vitamin B6

1984 ◽  
Vol 67 (3) ◽  
pp. 617-620
Author(s):  
Tomas R Guilarte
Keyword(s):  
Sodium Chloride ◽  
Potassium Chloride ◽  
Acid Hydrolysis ◽  
Salt Concentration ◽  
Vitamin B6 ◽  
Growth Response ◽  
Extraction Procedure ◽  
Food Samples ◽  
Microbiological Assay ◽  
Saccharomyces Uvarum

Abstract Acid hydrolysis is the most commonly used extraction procedure for the microbiological assay of vitamin B6 in food samples. Because NaCl or KC1 is formed as a result of the extraction procedure, these 2 salts were tested as possible agents that may influence the growth response of the yeasts Saccharomyces uvarum and Kloeckera brevis. Results indicate that NaCl and KC1 do effect the growth response of these 2 yeasts, depending on the salt concentration and the B6 vitamer present.

THE GLYCEROL DEHYDROGENASES OF PSEUDOMONAS SALINARIA, VIBRIO COSTICOLUS, AND ESCHERICHIA COLI IN RELATION TO BACTERIAL HALOPHILISM

1954 ◽  
Vol 32 (3) ◽  
pp. 206-217 ◽  
Author(s):  
R. M. Baxter ◽  
N. E. Gibbons
Keyword(s):  
Escherichia Coli ◽  
Sodium Chloride ◽  
Potassium Chloride ◽  
Salt Concentration ◽  
Halophilic Bacteria ◽  
Molar Concentration ◽  
Moderately Halophilic ◽  
E Coli ◽  
High Concentrations ◽  
Chloride Concentrations

Glycerol dehydrogenases from the extremely halophilic Pseudomonas salinaria and the moderately halophilic Vibrio costicolus are described and compared with the corresponding enzyme from the nonhalophilic Escherichia coli. The properties of all three enzymes are similar except their responses to salt concentration. The enzymes from E. coli and V. costicolus are most active at sodium chloride concentrations of about 0.25 M and 0.5 M respectively; that from P. salinaria is not only most active in the presence of 1.5 M NaCl but is irreversibly inactivated in the absence of salt. All three enzymes are more active in the presence of potassium chloride than of sodium chloride at any given molar concentration. These results suggest that the extremely halophilic bacteria contain high concentrations of salt and that their enzymes function maximally at these high concentrations. In contrast the moderately halophilic organisms contain relatively little salt and their enzymes are more comparable with those of nonhalophiles.

scholarly journals A study of calf thymus histone fraction F2(b) by gel filtration

1970 ◽  
Vol 120 (1) ◽  
pp. 61-66 ◽  
Author(s):  
P. A. Edwards ◽  
K. V. Shooter
Keyword(s):  
Sodium Chloride ◽  
Salt Concentration ◽  
Spherical Symmetry ◽  
Gel Filtration ◽  
Histone Fraction ◽  
Salting Out ◽  
Hydrodynamic Volume ◽  
Calf Thymus ◽  
Stokes Radius ◽  
The Individual

The gel-filtration behaviour of calf thymus histone fraction F2(b) was studied at three different salt concentrations (0.01m-, 0.10m- and 1.00m-sodium chloride) and two different pH ranges (pH3–4 and pH6.7–7.1). Other histone fractions [F1, F2(a) and F3] were also utilized to assist interpretation of the data. It was found that the Stokes radius of histone fraction F2(b) was not significantly changed when the salt concentration was increased, implying that the aggregation of the individual histone molecules (Edwards & Shooter, 1969) resulted in only relatively minor changes in the hydrodynamic volume. Aggregation would appear to be due to the salting out of hydrophobic regions giving rise, in the aggregate, to a compact core of hydrophobic groups from which protrude the remaining basic parts of the molecule. Repulsion between charged groups on the basic regions of individual histone molecules would give the aggregate approximately spherical symmetry, the diameter of the aggregate approximating to the length of a single histone molecule.

scholarly journals Purification and comparative properties of isoenzymes of nicotinamide–adenine dinucleotide phosphate–isocitrate dehydrogenase from rat heart and liver

1972 ◽  
Vol 129 (5) ◽  
pp. 1003-1011 ◽  
Author(s):  
M. Islam ◽  
Joyce L. Bell ◽  
D. N. Baron
Keyword(s):  
Myocardial Infarction ◽  
Ion Exchange ◽  
Ammonium Sulphate ◽  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Differential Sensitivity ◽  
Michaelis Constants ◽  
Ammonium Sulphate Fractionation ◽  
Cytoplasmic Location

1. Rat liver and heart major isoenzymes of NADP–isocitrate dehydrogenase have each been purified about 100-fold by a combination of ammonium sulphate fractionation and chromatography on ion-exchange cellulose and their properties compared. 2. The properties were similar in respect of pH, inhibition by Hg2+and Michaelis constants for isocitrate and NADP. 3. Some of the properties of the isoenzymes were different. 4. The heart isoenzyme was activated about 210% by 0.8m-ammonium sulphate whereas the liver isoenzyme was unaffected. The heart isoenzyme showed greater sensitivity to inactivation by heat (30°C for 30min), whereas the liver isoenzyme was more sensitive to inactivation by p-chloromercuribenzoate and by Cu2+. 5. The Michaelis constants with 3-acetylpyridine–adenine dinucleotide phosphate showed a twofold difference between liver and heart isoenzyme. 6. The differential sensitivity to heat and its mainly non-cytoplasmic location may be an explanation of the failure of plasma isocitrate dehydrogenase activity to increase after a myocardial infarction.

A Paramedic Treatment for Modeling Explicitly Solvated Chemical Reaction Mechanisms

2018 ◽  
Author(s):  
Yasemin Basdogan ◽  
John Keith
Keyword(s):  
Reaction Mechanism ◽  
Chemical Reaction ◽  
Reaction Mechanisms ◽  
Reaction Pathway ◽  
Optimization Procedure ◽  
Cost Effective ◽  
Chemical Reaction Mechanisms ◽  
Solvent Molecules ◽  
Dynamics Simulations ◽  
Mbh Reaction

<div> <div> <div> <p>We report a static quantum chemistry modeling treatment to study how solvent molecules affect chemical reaction mechanisms without dynamics simulations. This modeling scheme uses a global optimization procedure to identify low energy intermediate states with different numbers of explicit solvent molecules and then the growing string method to locate sequential transition states along a reaction pathway. Testing this approach on the acid-catalyzed Morita-Baylis-Hillman (MBH) reaction in methanol, we found a reaction mechanism that is consistent with both recent experiments and computationally intensive dynamics simulations with explicit solvation. In doing so, we explain unphysical pitfalls that obfuscate computational modeling that uses microsolvated reaction intermediates. This new paramedic approach can promisingly capture essential physical chemistry of the complicated and multistep MBH reaction mechanism, and the energy profiles found with this model appear reasonably insensitive to the level of theory used for energy calculations. Thus, it should be a useful and computationally cost-effective approach for modeling solvent mediated reaction mechanisms when dynamics simulations are not possible. </p> </div> </div> </div>

Salt effect in hydrolysis of 3-acyl-1,3-diphenyltriazenes

1981 ◽  
Vol 46 (12) ◽  
pp. 3104-3109 ◽  
Author(s):  
Miroslav Ludwig ◽  
Oldřich Pytela ◽  
Miroslav Večeřa
Keyword(s):  
Sodium Chloride ◽  
Temperature Dependence ◽  
Potassium Chloride ◽  
Rate Constants ◽  
Zinc Sulphate ◽  
Salt Effect ◽  
Sodium Sulphate ◽  
Potassium Sulphate ◽  
Lithium Sulphate ◽  
Hydrolysis Of

Rate constants of non-catalyzed hydrolysis of 3-acetyl-1,3-diphenyltriazene (I) and 3-(N-methylcarbamoyl)-1,3-diphenyltriazene (II) have been measured in the presence of salts (ammonium chloride, potassium chloride, lithium chloride, sodium chloride and bromide, ammonium sulphate, potassium sulphate, lithium sulphate, sodium sulphate and zinc sulphate) within broad concentration ranges. Temperature dependence of the hydrolysis of the substrates studied has been measured in the presence of lithium sulphate within temperature range 20° to 55 °C. The results obtained have been interpreted by mechanisms of hydrolysis of the studied substances.

Determination of Complex Reaction Mechanisms

2006 ◽  
Author(s):  
John Ross ◽  
Igor Schreiber ◽  
Marcel O. Vlad
Keyword(s):  
Reaction Mechanism ◽  
Reaction Mechanisms ◽  
Reaction Pathway ◽  
Chemical Species ◽  
Rate Coefficients ◽  
Chemical System ◽  
Evolutionary Development ◽  
Complex Reaction ◽  
Oscillatory Reactions

In a chemical system with many chemical species several questions can be asked: what species react with other species: in what temporal order: and with what results? These questions have been asked for over one hundred years about simple and complex chemical systems, and the answers constitute the macroscopic reaction mechanism. In Determination of Complex Reaction Mechanisms authors John Ross, Igor Schreiber, and Marcel Vlad present several systematic approaches for obtaining information on the causal connectivity of chemical species, on correlations of chemical species, on the reaction pathway, and on the reaction mechanism. Basic pulse theory is demonstrated and tested in an experiment on glycolysis. In a second approach, measurements on time series of concentrations are used to construct correlation functions and a theory is developed which shows that from these functions information may be inferred on the reaction pathway, the reaction mechanism, and the centers of control in that mechanism. A third approach is based on application of genetic algorithm methods to the study of the evolutionary development of a reaction mechanism, to the attainment given goals in a mechanism, and to the determination of a reaction mechanism and rate coefficients by comparison with experiment. Responses of non-linear systems to pulses or other perturbations are analyzed, and mechanisms of oscillatory reactions are presented in detail. The concluding chapters give an introduction to bioinformatics and statistical methods for determining reaction mechanisms.

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