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How important are entropic contributions to enzyme catalysis?
J Villa1, M Strajbl, T M Glennon
1Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
Summary
Enzymes accelerate reactions less through entropy than previously thought. Computer simulations reveal that enzyme binding does not fully restrict motion, and binding entropy differs from solution reaction entropy.
Area of Science:
- Biochemistry
- Computational Chemistry
- Enzymology
Background:
- The prevailing theory suggests enzymes accelerate reactions by reducing entropy via binding.
- This implies enzyme active sites freeze reactant motion, lowering activation energy.
- Experimental validation of this entropic proposal is challenging.
Purpose of the Study:
- To rigorously define the entropic proposal in enzyme catalysis.
- To develop a computational method for quantifying entropic contributions to activation energy.
- To compare the entropic effects in enzymatic versus solution reactions.
Main Methods:
- Development of a novel computer simulation approach.
- Calculation of activation entropy (ΔS‡) for enzymatic and solution reactions.
- Application of the method to the subtilisin catalytic reaction.
Main Results:
- The entropic contribution to subtilisin catalysis is significantly smaller than hypothesized.
- Identified that many motions remain unfrozen in the enzyme's transition state.
- Demonstrated that enzyme binding does not completely eliminate motional freedom.
- Showed that binding entropy does not necessarily equal solution activation entropy.
Conclusions:
- Enzyme catalysis is less reliant on entropic reduction through binding than previously assumed.
- Computational simulations provide a robust method for dissecting entropic contributions.
- The study refines our understanding of the mechanisms underlying enzyme efficiency.