scholarly journals The effects of magnesium ions on the interactions of ox brain and liver glutamate dehydrogenase with ATP and GTP

1984 ◽  
Vol 220 (3) ◽  
pp. 853-855 ◽  
Author(s):  
A D McCarthy ◽  
K F Tipton
Keyword(s):  
Complex Formation ◽  
Glutamate Dehydrogenase ◽  
Enzyme Reaction ◽  
Magnesium Ions ◽  
Free Nucleotide ◽  
Regulatory Actions

The effects of ATP and GTP on the activities of ox liver and brain glutamate dehydrogenase were determined in the absence and presence of added Mg2+ ions. Although GTP was an inhibitor of the enzyme reaction assayed in the direction of NAD+ reduction, the magnesium complex of this nucleotide had no effect on the activity. Similarly the magnesium complex of ATP was without effect on the activity of the enzyme although the free nucleotide was an activator. These results suggest that it is important to take account of magnesium complex formation when considering the regulatory actions of these nucleotides.

scholarly journals Activation of brain hexokinase by magnesium ions and by magnesium ion–adenosine triphosphate complex

1972 ◽  
Vol 130 (1) ◽  
pp. 63-69 ◽  
Author(s):  
Daniel L. Purich ◽  
Herbert J. Fromm
Keyword(s):  
Simple Model ◽  
Complex Formation ◽  
Kinetic Data ◽  
Alternative Explanation ◽  
Metal Substrate ◽  
Magnesium Ion ◽  
Magnesium Ions ◽  
Substrate Complex ◽  
The Brain ◽  
Hill Plots

1. An alternative explanation for the kinetic data obtained by Bachelard (1971) for the brain hexokinase reaction is presented. 2. Apparently sigmoidal saturation curves for MgATP2− based upon Bachelard's (1971) studies can be corrected to hyperbolic curves by use of a stability constant for MgATP2− complex formation. 3. A number of other effects related to the concentration-dependent stability of the MgATP2− complex and to the presence of the inhibitory free uncomplexed ATP4− concentration are also explained in terms of a non-allosteric role for either Mg2+ or MgATP2− fully consistent with a number of previous reports on this enzyme. 4. A brief discussion of the validity of Hill plots in studies of multisubstrate co-operative enzymes is presented. 5. A simple model is presented that demonstrates how enzymes obeying Michaelis–Menten kinetics can demonstrate sigmoidal velocity responses if the true substrate of the reaction is the metal–substrate complex.

Complex formation equilibria of phosphocreatine with sodium, potassium and magnesium ions

Polyhedron ◽  
2002 ◽  
Vol 21 (14-15) ◽  
pp. 1481-1484 ◽  
Author(s):  
Franco Cecconi ◽  
Chiara Frassineti ◽  
Peter Gans ◽  
Stefano Iotti ◽  
Stefano Midollini ◽  
...  
Keyword(s):  
Complex Formation ◽  
Magnesium Ions ◽  
Complex Formation Equilibria ◽  
Sodium Potassium ◽  
Formation Equilibria

Chemical inhibition used in a kinetic urease/glutamate dehydrogenase method for urea in serum.

1979 ◽  
Vol 25 (10) ◽  
pp. 1721-1729 ◽  
Author(s):  
E J Sampson ◽  
M A Baird
Keyword(s):  
Glutamate Dehydrogenase ◽  
Flow Analysis ◽  
Enzyme Reaction ◽  
Complete Recovery ◽  
Fixed Time ◽  
Time Interval ◽  
Michaelis Constant ◽  
Dehydrogenase Reaction ◽  
Diacetyl Monoxime ◽  
Sample Dilution

Abstract We describe a fixed-time-interval, kinetic inhibition method, with use of a competitive inhibitor (l) of the urease/glutamate dehydrogenase reaction to increase the "apparent" Michaelis constant by a factor of (1 + [l]lKl). This allows greater flexibility in selecting an appropriate sample dilution for kinetic determinations of urea in serum (i.e., [S]lKm ratio). Nine compounds were screened as potential inhibitors for this study. Adding 5 mmol of hydroxyurea per liter increases the "apparent" Michaelis constant for the coupled enzyme reaction by 10-fold. We used a sample dilution of 21-fold vs. dilutions of 141- to 350-fold for previously reported kinetic methods. Mean analytical recovery with this method was 100.2%. Reaction rate vs. urea concentration was linear, and complete recovery extended to 30 mmol of urea per liter. Of 22 potential interferents, only fluoride (250 mmol/L) and bilirubin (1 mmol/L, or 580 mg/L) caused greater than 5% interference. We discuss precision and effects of specimen dilution, and compare results for 100 specimens with those by a manual Berthelot-indophenol method, a manual diacetyl monoxime method, and a diacetyl monoxime method adapted to continuous-flow analysis.

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