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.

These mechanisms can operate individually or together, depending on the enzyme and the chemical transformation involved.