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The Importance of Correct Protein Concentration for Kinetics and Affinity Determination in Structure-function Analysis
Published on: March 17, 2010
How much do enzymes really gain by restraining their reacting fragments?
1Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062, USA.
Journal of the American Chemical Society
|April 11, 2002
Summary
Steric effects are not the primary driver of enzyme catalysis. Computer simulations reveal electrostatic interactions, not steric forces, are key to haloalkane dehalogenase
Area of Science:
- Biochemistry
- Computational Chemistry
- Enzyme Catalysis
Background:
- Enzyme catalysis is often attributed to steric effects, pushing substrates into a near-attack configuration (NAC).
- The role of steric contributions versus electrostatic forces in enzyme catalysis remains a subject of investigation.
- Haloalkane dehalogenase serves as a model enzyme for studying catalytic mechanisms.
Purpose of the Study:
- To quantitatively assess the relative importance of steric effects in enzyme catalysis using computer simulations.
- To differentiate between steric and electrostatic contributions to the catalytic power of haloalkane dehalogenase.
Main Methods:
- Utilized empirical valence bond (EVB) method to model reaction potential surfaces.
- Employed thermodynamic cycles to compare enzymatic reactions with reactions in water.
- Developed two computational strategies: substrate restraints in water and elimination of electrostatic interactions.
Main Results:
- The nonelectrostatic (steric) contribution to catalysis was found to be approximately -0.7 kcal/mol.
- The apparent steric effect, including electrostatic contributions, was -2.2 kcal/mol.
- Electrostatic interactions accounted for the majority of the catalytic effect, approximately -6.1 kcal/mol.
Conclusions:
- Steric effects are not the major source of catalytic power in haloalkane dehalogenase.
- Electrostatic interactions play a dominant role in the enzyme's catalytic efficiency.
- The apparent steric effect is significantly influenced by solvent reorganization energy, challenging traditional views.
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