scholarly journals The nature of carbon dioxide substrate and equilibrium constant of the 6-phosphogluconate dehydrogenase reaction

1969 ◽  
Vol 115 (4) ◽  
pp. 633-638 ◽  
Author(s):  
R. H. Villet ◽  
K. Dalziel
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Equilibrium Constant ◽  
Heat Of Reaction ◽  
Phosphogluconate Dehydrogenase ◽  
Sheep Liver ◽  
Dehydrogenase Reaction ◽  
Reductive Carboxylation ◽  
Primary Substrate

1. It was shown that dissolved CO2 and not HCO3− or H2CO3 is the primary substrate for reductive carboxylation with 6-phosphogluconate dehydrogenase from sheep liver. 2. The equilibrium constant of the reaction was measured in solutions of various ionic strengths and at several temperatures, and the free energy and heat of reaction were determined.

scholarly journals The mechanisms of reductive carboxylation reactions. Carbon dioxide or bicarbonate as substrate of nicotinamide-adenine dinucleotide phosphate-linked isocitrate dehydrogenase and ‘malic’ enzyme

1968 ◽  
Vol 110 (2) ◽  
pp. 223-230 ◽  
Author(s):  
K. Dalziel ◽  
J. C. Londesborough
Keyword(s):  
Carbon Dioxide ◽  
Isocitrate Dehydrogenase ◽  
Malic Enzyme ◽  
Time Course ◽  
Kinetic Method ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Quantitative Agreement ◽  
Effects Of Ph ◽  
Reductive Carboxylation ◽  
Primary Substrate

1. A simple kinetic method was devised to show whether dissolved CO2 or HCO3– ion is the substrate in enzyme-catalysed carboxylation reactions. 2. The time-course of the reductive carboxylation of 2-oxoglutarate by NADPH, catalysed by isocitrate dehydrogenase, was studied by a sensitive fluorimetric method at pH7·3 and pH6·4, with large concentrations of substrate and coenzyme and small carbon dioxide concentrations. 3. Reaction was initiated by the addition of carbon dioxide in one of three forms: (i) as the dissolved gas in equilibrium with bicarbonate; (ii) as unbuffered bicarbonate solution; (iii) as the gas or as an unbuffered solution of the gas in water. Different progress curves were obtained in the three cases. 4. The results show that dissolved CO2 is the primary substrate of the enzyme, and that HCO3– ion is at best a very poor substrate. The progress curves are in quantitative agreement with this conclusion and with the known rates of the reversible hydration of CO2 under the conditions of the experiments. The effects of carbonic anhydrase confirm the conclusions. 5. Similar experiments on the reductive carboxylation of pyruvate catalysed by the ‘malic’ enzyme show that dissolved CO2 is the primary substrate of this enzyme also. 6. The results are discussed in relation to the mechanisms of these enzymes, and the effects of pH on the reactions. 7. The advantages of the method and its possible applications to other enzymes involved in carbon dioxide metabolism are discussed.

scholarly journals The equilibrium constant of the isocitrate dehydrogenase reaction

1968 ◽  
Vol 110 (2) ◽  
pp. 217-222 ◽  
Author(s):  
J. C. Londesborough ◽  
K. Dalziel
Keyword(s):  
Ionic Strength ◽  
Equilibrium Constant ◽  
Isocitrate Dehydrogenase ◽  
Ion Concentration ◽  
Oxidative Decarboxylation ◽  
Heat Of Reaction ◽  
Dehydrogenase Reaction

1. The equilibrium constant for oxidative decarboxylation of isocitrate by NADP+, catalysed by isocitrate dehydrogenase, was measured in solutions of various ionic strengths and at several temperatures. 2. Thermodynamic values for the reaction were obtained by extrapolation to zero ionic strength, and the heat of reaction was estimated. 3. The effect of Mg2+ ion concentration on the equilibrium was studied.

Chemical equilibrium and chemical kinetics

2018 ◽  
Author(s):  
Dennis Sherwood ◽  
Paul Dalby
Keyword(s):  
Free Energy ◽  
Equilibrium Constant ◽  
Gibbs Free Energy ◽  
Chemical Kinetics ◽  
Chemical Equilibrium ◽  
First Principles ◽  
Effect Of Temperature ◽  
Total System ◽  
Free Energies

Building on the previous chapter, this chapter examines gas phase chemical equilibrium, and the equilibrium constant. This chapter takes a rigorous, yet very clear, ‘first principles’ approach, expressing the total Gibbs free energy of a reaction mixture at any time as the sum of the instantaneous Gibbs free energies of each component, as expressed in terms of the extent-of-reaction. The equilibrium reaction mixture is then defined as the point at which the total system Gibbs free energy is a minimum, from which concepts such as the equilibrium constant emerge. The chapter also explores the temperature dependence of equilibrium, this being one example of Le Chatelier’s principle. Finally, the chapter links thermodynamics to chemical kinetics by showing how the equilibrium constant is the ratio of the forward and backward rate constants. We also introduce the Arrhenius equation, closing with a discussion of the overall effect of temperature on chemical equilibrium.

Studies in the Vulcanization of Rubber. I—Thermochemistry of Vulcanization of Rubber

1930 ◽  
Vol 3 (4) ◽  
pp. 631-639
Author(s):  
John T. Blake
Keyword(s):  
Free Energy ◽  
Internal Energy ◽  
Chemical Reaction ◽  
Effect Of Temperature ◽  
Heat Of Reaction ◽  
Chemical Affinity ◽  
Direct Measure ◽  
Total Change

Abstract WHEN a chemical reaction takes place, it is usually accompanied by an absorption or evolution of heat. The amount of the heat interchange is not a direct measure of the chemical affinity involved in the reaction, nor is it a measure of the free energy of the reaction. The heat of reaction, however, is a measure of the total change in internal energy and is of importance, therefore, in calculating the effect of temperature on a reaction and in elucidating the mechanism of it.

Cloning, Expression, Purification, and Characterization of the 6-Phosphogluconate Dehydrogenase from Sheep Liver

1998 ◽  
Vol 13 (2) ◽  
pp. 251-258 ◽  
Author(s):  
Lilian Chooback ◽  
Nancy E. Price ◽  
William E. Karsten ◽  
John Nelson ◽  
Paula Sundstrom ◽  
...  
Keyword(s):  
Purification And Characterization ◽  
Phosphogluconate Dehydrogenase ◽  
Sheep Liver

scholarly journals Purification and properties of 6-phosphogluconate dehydrogenase from sheep liver

1969 ◽  
Vol 115 (4) ◽  
pp. 639-643 ◽  
Author(s):  
R. H. Villet ◽  
K. Dalziel
Keyword(s):  
Molecular Weight ◽  
Gel Electrophoresis ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sedimentation Velocity ◽  
Sedimentation Equilibrium ◽  
Equilibrium Studies ◽  
Phosphogluconate Dehydrogenase ◽  
Sheep Liver ◽  
Equilibrium Sedimentation ◽  
Purification And Properties

A method is described for the isolation of 6-phosphogluconate dehydrogenase from sheep liver. The product appears to be homogeneous in polyacrylamide-gel electrophoresis and in sedimentation-velocity and sedimentation-equilibrium studies in the ultracentrifuge. The molecular weight is estimated as 129000 from equilibrium sedimentation.

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