Mechanism of Enzyme Action

Catalysis is a method in which the rate of reaction is increased by the addition of a catalyst. At the end of the reaction, the catalyst is not consumed and is ready to be used once again.

Enzyme catalysis is a biological process of the increasing rate of biochemical reaction by adding the enzyme. An enzyme acts as a catalyst and speeds up the chemical reaction without being used and work repeatedly. Let’s study in detail the mechanism of enzyme action.

Mechanism of enzyme action

An enzyme is a globular structure made up of unique amino acid sequences that coil over themselves to construct a specific enzyme structure. Some specific amino acids composition allow the enzyme to perform specific functions.

Active site

Out of hundreds of amino acids making an enzyme structure, only some amino acids (about 3-4) occupy a specific region called the active site. While the rest of the amino acids are involved in the maintenance of the globular structure of an enzyme. The active site is responsible for the binding of substrate and catalysis function. The substrate is any substance on which the enzyme acts and breaks it down into products.

The active site has two parts i.e., binding site and catalytic site. The binding site is responsible for the recognition and binding of a specific substrate, while the catalytic site is involved in its breakdown.

Enzyme-catalyzed chemical reaction

Mechanism of enzyme action can be summarized in aone equation.

mechanism of enzyme action equation

During an enzyme-catalyzed chemical reaction, in an aqueous medium, the substrate (S) comes closer to the enzyme (E) at the active site. The binding site identifies the substrate and helps in its binding with the enzyme by developing chemical bonds to generate enzyme-substrate complex (ES complex). After it's proper binding and generation of the enzyme-substrate complex, catalytic sites break it down into products (P). The enzyme then detaches itself from the products unchanged and is ready to perform another reaction. This reaction is shown in diagram below:

mechanism of enzyme action
Mechanism of enzyme action

Models of mechanism of enzyme action

To explain the mechanism of enzyme action two models have been proposed by scientists.

Lock and key model

This model was proposed by Emil Fischer in 1894 to explain the substrate specificity of the enzyme. According to this model, the only substrate with a specific shape can bind to the enzyme at an active site to be converted into products, as the specific key can open a specific lock. The change of substrate and active site and complementary to each other and the non-complementary substrate cannot bind with the enzymes. The enzyme is a rigid structure and no modification takes place in the active site during the binding process.

Induced fit model

This model was proposed by Koshland in 1959 based on new shreds of evidence. This model replaced the lock and key model due to a better explanation of the enzyme-catalyzed reaction. This model emphasizes that substrate induces conformational changes in the active site to properly fit during the binding process. These changes help the enzyme to effectively perform its catalysis function.

Video lesson


  • Singh, A. K., & Tiwari, I. (2020). Nanomaterial Synthesis and Mechanism for Enzyme Immobilization: Part II. In Nanomaterials in Biofuels Research (pp. 191-212). Springer, Singapore.
  • Mildvan, A. S. (1974). Mechanism of enzyme action. Annual Review of Biochemistry, 43(1), 357-399.
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