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Obfuscation of allosteric structure-function relationships by enthalpy-entropy compensation
V L Tlapak-Simmons1, G D Reinhart
1Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128 USA.
Biophysical Journal
|July 24, 1998
Summary
This study investigated phosphofructokinase (PFK) allosteric properties. pH changes affect ligand binding and inhibition/activation, but not catalytic rate, revealing complex thermodynamic compensation.
Area of Science:
- Biochemistry
- Enzyme kinetics
- Protein allostery
Background:
- Phosphofructokinase (PFK) is a key glycolytic enzyme.
- Allosteric regulation allows fine-tuning of enzyme activity.
- Understanding PFK regulation is crucial for metabolic control.
Purpose of the Study:
- To investigate the pH and temperature dependence of PFK allosteric properties.
- To elucidate the thermodynamic basis of allosteric ligand interactions.
- To correlate molecular perturbations with functional consequences.
Main Methods:
- Studied PFK from Bacillus stearothermophilus across a pH range (5-9) and temperature range (6-40°C).
- Analyzed the effects of allosteric ligands MgADP and phospho(enol)pyruvate (PEP) on enzyme kinetics.
- Determined dissociation constants and coupling free energies.
Main Results:
- Allosteric ligands MgADP and PEP did not affect the catalytic rate (kcat) within the studied ranges.
- Increased pH enhanced PEP inhibition and MgADP activation, despite slightly reduced ligand affinity.
- Enthalpy and entropy contributions to binding energy diminished with increasing pH.
Conclusions:
- The functional consequences of allosteric ligand binding do not directly correlate with the magnitude of molecular perturbations.
- Temperature and pH modulate allosteric behavior by altering the balance of enthalpy and entropy.
- Thermodynamic compensation plays a significant role in PFK allosteric regulation.