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Temperature-induced inversion of allosteric phenomena
B L Braxton1, V L Tlapak-Simmons, G D Reinhart
1Department of Chemistry and Biochemistry, University of Oklahoma, Norman 73019.
The Journal of Biological Chemistry
|January 7, 1994
Summary
Temperature changes can reverse how allosteric ligands affect enzyme activity, shifting from inhibition to activation. This occurs due to altered enzyme-substrate affinity, not activation energy changes, highlighting thermodynamic influences.
Area of Science:
- Biochemistry
- Enzymology
- Biophysics
Background:
- Allosteric ligands modulate enzyme activity by binding to sites distinct from the active site.
- Understanding the mechanisms of allosteric regulation is crucial for enzyme function and drug development.
Purpose of the Study:
- To investigate how temperature influences the allosteric effects of ligands on enzyme activity.
- To elucidate the thermodynamic basis of temperature-dependent allosteric modulation.
Main Methods:
- Studied carbamoyl-phosphate synthetase from Escherichia coli and phosphofructokinase from Bacillus stearothermophilus.
- Analyzed the temperature-dependent changes in enzyme-ligand interactions and enzyme-substrate affinity.
- Utilized thermodynamic analysis of coupling free energy (ΔH and ΔS components).
Main Results:
- Increasing temperature reversed allosteric ligand effects from inhibition to activation for both enzymes.
- Observed effects were attributed to temperature-dependent changes in enzyme-substrate affinity, not altered activation energy.
- Thermodynamic parameters (ΔH and ΔS) quantitatively explained the observed allosteric ligand behavior.
Conclusions:
- Temperature significantly impacts allosteric ligand efficacy by altering enzyme-substrate binding affinity.
- Thermodynamic factors (enthalpy and entropy) are key to understanding these temperature-dependent allosteric effects.
- Structural changes alone, as seen in crystallography, may not fully explain allosteric ligand mechanisms.