9.12.3 Nature of Enzyme Action

Each enzyme (E) has a substrate (S) binding site in its molecule so that a highly reactive enzyme-substrate complex (ES) is produced. This complex is short-lived and dissociates into its product(s) P and the unchanged enzyme with an intermediate formation of the enzyme-product complex (EP). The formation of the ES complex is essential for catalysis. E + S ˆ ˆ ˆ† ‡ ˆ ˆˆ ES ⎯ →⎯ EP ⎯ →⎯ E + P

The catalytic cycle of an enzyme action can be described in the following

  • First, the substrate binds to the active site of the enzyme, fitting into the active site.
  • The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate.
  • The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new enzyme- product complex is formed.
  • The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again.

 

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