Temperature-Dependent Transition in L-Histidine Ammonia-Lyase

1973 ◽  
Vol 51 (5) ◽  
pp. 556-559 ◽  
Author(s):  
Ronald W. McClard ◽  
Harold M. Kolenbrander
Keyword(s):  
Transition Temperature ◽  
Equilibrium Constant ◽  
Energy Of Activation ◽  
Multiple Forms ◽  
Temperature Dependent ◽  
Arrhenius Plots ◽  
Apparent Equilibrium Constant ◽  
Effects Of Temperature ◽  
Apparent Equilibrium

The effects of temperature on the energy of activation, the enthalpy of binding, and the apparent equilibrium constant for the overall reaction catalyzed by L-histidine ammonia-lyase (EC 4.3.1.3) have been determined. A temperature-dependent transition (at approximately 30°) involving multiple forms of the enzyme is also discussed.The enthalpy of binding is exothermic above 30° and endothermic below this transition temperature. In addition, a bend is observed in the Arrhenius plots at approximately 34°. The combination of these effects suggests the existence of at least two forms of the enzyme.

Immunochemical approach to the question of inactive subunits in cases of lactate dehydrogenase B subunit deficiency.

1986 ◽  
Vol 32 (1) ◽  
pp. 116-119 ◽  
Author(s):  
M Maekawa ◽  
K Sudo ◽  
T Kanno
Keyword(s):  
Lactate Dehydrogenase ◽  
Equilibrium Constant ◽  
Competitive Reaction ◽  
Apparent Equilibrium Constant ◽  
B Subunit ◽  
B Subunits ◽  
Free Antigen ◽  
Apparent Equilibrium ◽  
Normal Controls

Abstract If there were enzymatically inactive B subunits in a solution containing lactate dehydrogenase (LD) B4 prepared from the hemolysates of heterozygous individuals with LD-B subunit deficiency, the inactive subunits would compete with normal subunits for antibodies to the B4 subunit. Using the activity of normal LD-B4 as an index, we could ascertain the proportion of free antigen (LD-B4) and antibody-antigen complexes (LD-B4-anti-LD-B4) and calculate the apparent equilibrium constant, Keq. Doing so, we found the value for Keq in LD-B subunit deficiency to be smaller than that for normal controls. Evidently the expected competitive reaction takes place. We conclude that heterozygous individuals with LD-B subunit deficiency do indeed produce variant (enzymatically inactive) B subunits of LD.

The oxidation of ferrocytochrome c in nonbinding buffer

1977 ◽  
Vol 55 (8) ◽  
pp. 796-803 ◽  
Author(s):  
B. F. Peterman ◽  
R. A. Morton
Keyword(s):  
Ionic Strength ◽  
Cytochrome C ◽  
Equilibrium Constant ◽  
Oxidation Reaction ◽  
Potassium Phosphate ◽  
Ionic Strength Dependence ◽  
Horse Heart Cytochrome ◽  
Apparent Equilibrium Constant ◽  
Diffusion Limited ◽  
Apparent Equilibrium

The apparent equilibrium constant and rate of oxidation was investigated for the reaction of cytochrome c with iron hexacyanide. It was found that if horse heart ferricytochrome c was exposed to ferricyanide (to oxidize traces of reduced protein) the cytochrome subsequently, even after extensive dialysis, had an apparent equilibrium constant different from that of electrodialyzed protein. The effect of ferricyanide ion apparently cannot be removed by ordinary dialysis. The ionic strength dependence of the apparent equilibrium constant and bimolecular oxidation rate constant was measured in the range 1–200 mM using Tris–cacodylate or potassium phosphate buffers at pH 7.0, and electrodialyzed horse heart cytochrome c. The oxidation reaction proceeded very rapidly. Extrapolated to zero ionic strength, kox(~ 9 × 109 M−1 s−1) was about 7% of that calculated for a diffusion-limited reaction. Since the exposed heme edge occupies only the order of 3% of the surface area, electron transfer apparently results at nearly every collision with the active-site region. An effective charge of + 7.8 units was estimated for the oxidation reaction. The rate of oxidation of Pseudomonas aeruginosa c551 was much slower (kox at μ = 0 was the order of 6 × 103), and was not consistent with diffusion-limited kinetics.

Solubility of Na2O2.8 H2O in the system H2O2-NaOH-KOH-H2O

1982 ◽  
Vol 47 (3) ◽  
pp. 736-743 ◽  
Author(s):  
Jan Balej ◽  
Otomar Špalek
Keyword(s):  
Equilibrium Constant ◽  
Potassium Hydroxide ◽  
Empirical Equation ◽  
Multicomponent System ◽  
Total Content ◽  
Potassium Ions ◽  
Apparent Equilibrium Constant ◽  
Dissolution Reaction ◽  
Apparent Equilibrium

The solubility of Na2O2.8 H2O in the multicomponent system H2O2-NaOH-KOH-H2O has been investigated at temperatures of 12, 20, and 30°C. Comparison of the data with solubilities of the same compound in the simler system H2O2-NaOH-H2) shows that the presence of potassium hydroxide increases the solubility at the same temperature and total content of hydroxide ions. The effect of potassium ions on the solubility of Na2O2.8 H2O is expressed by an empirical equation relating the apparent equilibrium constant of the dissolution reaction and the molalities of the perhydroxyl and potassium ions at a given temperature.

scholarly journals Apparent equilibrium constant and mass-action ratio for sucrose-phosphate synthase in seeds of Pisum sativum

1990 ◽  
Vol 267 (3) ◽  
pp. 739-743 ◽  
Author(s):  
J E Lunn ◽  
T ap Rees
Keyword(s):  
Pisum Sativum ◽  
Equilibrium Constant ◽  
Equilibrium Constants ◽  
Sucrose Phosphate Synthase ◽  
Mass Action ◽  
Apparent Equilibrium Constant ◽  
Apparent Equilibrium ◽  
Sucrose Phosphate ◽  
Phosphate Synthase

The aim of this work was to use preparations from germinating seeds of Pisum sativum to determine the apparent equilibrium constant of the reaction catalysed by sucrose-phosphate synthase (EC 2.4.1.14) and to compare this with the mass-action ratio of the reaction in the seeds. The apparent equilibrium constant ranged from 5.3 at 0.25 mM-MgCl2, pH 7.0, to 62 at 10 mM-MgCl2, pH 7.5. The sucrose phosphate content of the seeds, 23 nmol/g fresh wt., was determined by separating sucrose phosphate from sucrose by ion-exchange chromatography and then measuring the sucrose released by alkaline phosphatase. Comparison of equilibrium constants and mass-action ratios in the cotyledons of 38 h-germinated seeds showed that the reactions catalysed by glucose-6-phosphate isomerase, phosphoglucomutase and UDP-glucose pyrophosphorylase are close to equilibrium, and those catalysed by sucrose-phosphate synthase and sucrose phosphatase are considerably displaced from equilibrium in vivo.

scholarly journals THE pH AND pD DEPENDENCE OF THE SPONTANEOUS AND MAGNESIUM-ION-CATALYZED DECARBOXYLATION OF OXALACETIC ACID

1964 ◽  
Vol 42 (2) ◽  
pp. 403-415 ◽  
Author(s):  
George W. Kosicki ◽  
Stanislava N. Lipovac
Keyword(s):  
Equilibrium Constant ◽  
Spectral Data ◽  
Magnesium Ion ◽  
Equilibrium System ◽  
Acid Anion ◽  
Oxalacetic Acid ◽  
Apparent Equilibrium Constant ◽  
Apparent Equilibrium

Spectrophotometric studies of the spontaneous and magnesium-ion-catalyzed decarboxylation of oxalacetic acid in H2O and D2O have been carried out over a range of pH, pD, and magnesium ion concentrations.The rate of decarboxylation of oxalacetic acid depends on the proposed equilibrium system between the acid anion and magnesium chelate under a variety of conditions.The absorbancy indexes and the apparent equilibrium constant of the keto and enol forms of the magnesium chelate were estimated from a combination of the kinetic and spectral data.

scholarly journals Magnesium Signaling in Plants

2021 ◽  
Vol 22 (3) ◽  
pp. 1159
Author(s):  
Leszek A. Kleczkowski ◽  
Abir U. Igamberdiev
Keyword(s):  
Equilibrium Constant ◽  
Adenylate Kinase ◽  
Nucleoside Diphosphate Kinase ◽  
Phloem Loading ◽  
Photosynthetic Performance ◽  
Fine Tuning ◽  
Primary Control ◽  
Membrane Bound ◽  
Free Magnesium ◽  
Apparent Equilibrium

Free magnesium (Mg2+) is a signal of the adenylate (ATP+ADP+AMP) status in the cells. It results from the equilibrium of adenylate kinase (AK), which uses Mg-chelated and Mg-free adenylates as substrates in both directions of its reaction. The AK-mediated primary control of intracellular [Mg2+] is finely interwoven with the operation of membrane-bound adenylate- and Mg2+-translocators, which in a given compartment control the supply of free adenylates and Mg2+ for the AK-mediated equilibration. As a result, [Mg2+] itself varies both between and within the compartments, depending on their energetic status and environmental clues. Other key nucleotide-utilizing/producing enzymes (e.g., nucleoside diphosphate kinase) may also be involved in fine-tuning of the intracellular [Mg2+]. Changes in [Mg2+] regulate activities of myriads of Mg-utilizing/requiring enzymes, affecting metabolism under both normal and stress conditions, and impacting photosynthetic performance, respiration, phloem loading and other processes. In compartments controlled by AK equilibrium (cytosol, chloroplasts, mitochondria, nucleus), the intracellular [Mg2+] can be calculated from total adenylate contents, based on the dependence of the apparent equilibrium constant of AK on [Mg2+]. Magnesium signaling, reflecting cellular adenylate status, is likely widespread in all eukaryotic and prokaryotic organisms, due simply to the omnipresent nature of AK and to its involvement in adenylate equilibration.

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