Mechanisms of Enzyme Catalysis

Enzymes accelerate chemical reactions by lowering the activation energy required for the conversion of substrates into products. They do not change the overall free-energy difference between reactants and products or alter the equilibrium position of a reaction.

Several mechanisms contribute to enzyme catalysis:

• Acid-base catalysis: Specific amino acid residues donate or accept protons during a reaction.
• Covalent catalysis: The enzyme forms a temporary covalent intermediate with the substrate.
• Metal-ion catalysis: Metal ions help stabilize charged intermediates or facilitate electron transfer.
• Proximity and orientation effects: The enzyme positions substrates in favorable orientations, increasing the probability of productive interactions.
• Transition-state stabilization: The active site preferentially stabilizes the transition state, reducing the energy barrier for the reaction.