Properties of Enzyme Active Sites

Overview

• Active sites are crucial regions on enzymes where substrates bind.
• Enzymes have similar properties, and their active sites share important characteristics.

Six Major Properties of Active Sites

1. Binding and Catalysis

• Location: Active sites are 3D regions on enzymes for substrate binding.
• Components: Consist of residues (amino acids) that bind substrates and catalytic groups for reaction catalysis.

2. Stabilization of Transition States

• Active sites stabilize the transition state and facilitate bond formation/breaking.
• Catalytic groups speed up reactions by lowering the energy of the transition state.

3. Microenvironment Creation

• Active sites create nonpolar microenvironments by excluding water unless it is a reactant.
• These environments orient reactants favorably, reducing unwanted reactions and product formation.

4. Small Proportion of Enzyme

• Active sites are small relative to the whole enzyme.
• Residues are far apart on the polypeptide chain, requiring enzyme folding to bring them close together.
• The remaining enzyme structure supports and stabilizes the active site.
• Allosteric Sites: Other sites on enzymes that regulate function and interact with components like cell membranes.

5. Reversible Binding

• Substrates bind reversibly to active sites via non-covalent interactions (e.g., hydrogen bonds, hydrophobic interactions).
• Reversible binding allows for product release after substrate conversion.

6. Structural Complementarity

• The substrate's shape must be complementary to the active site to facilitate binding.
• Models of Binding:
  • Lock and Key Model: Substrate fits perfectly into an enzyme's active site due to complementary shapes pre-binding.
  • Induced Fit Model: Active site adapts to the substrate's shape upon binding, becoming complementary.

Conclusion

• Active sites are essential for enzyme function, involving precise interactions and complementarity.
• The induced fit model provides a more accurate depiction of substrate-enzyme interaction.