Enzyme Catalysis


Learning Objective

  • List the five typical mechanisms used by enzymes to catalyze biological reactions

Key Points

    • Enzymes are a special class of catalyst that can accelerate biochemical reactions.
    • Enzymes are proteins that bind reactants, or substrates, in regions called active sites.
    • Upon binding, conformational changes in enzymes result in stabilization of the transition state complex, lowering the activation energy of a reaction.


  • active siteThe area within an enzyme where the substrate binds.
  • substrateThe reactant(s) involved in a biochemical reaction catalyzed by an enzyme.
  • enzymeA globular protein that catalyzes a biological chemical reaction.

Synthetic catalysts are used to accelerate a variety of industrial processes and are crucial to the chemical manufacturing industry. However, catalysts are also found in nature in the form of enzymes. Enzymes are proteins that are able to lower the activation energy for various biochemical reactions. They do this by binding the reactant(s), known as the substrate(s), to an active site within the enzyme. At the active site, the substrate(s) can form an activated complex at lower energy. Once the reaction completes, the product(s) leaves the active site, so the enzyme is free to catalyze more reactions.

Enzyme catalysisAn enzyme catalyzes a biochemical reaction by binding a substrate at the active site. After the reaction has proceeded, the products are released and the enzyme can catalyze further reactions.

The Induced Fit Model

One model of enzyme mechanism is called the induced fit model. This model proposes that the binding of the reactant, or substrate, to the enzyme active site results in a conformational change to the enzyme. This change stabilizes the transition state complex, and thus lowers the activation energy.

Ways That Enzymes Catalyze Reactions

Enzymes can catalyze reactions through a variety of mechanisms. Some of these include:

  • Bond strain: enzymes can destabilize bonds within the substrate.
  • Proximity and orientation: conformational changes in the enzyme upon substrate binding can bring reactive groups closer together or orient them so they can react.
  • Proton donors and acceptors: the presence of acidic or basic groups can affect bond polarization and reaction speed.
  • Electrostatic catalysis: electrostatic attractions between the enzyme and the substrate can stabilize the activated complex.
  • Covalent catalysis: covalent bonding to side chains or cofactors can lower the energy of the transition state.

As such, enzymes show that evolutionary biology has produced highly effective catalysts.