BIOCHEMISTRY - Key Regulators and Biological Fluids of the Human Body - 2016

1. ENZYMES

1.3. Mechanism of Enzyme Action

The contact between an enzyme (E) and a substrate (S) occurs via the Active Site, which is typically a small region of the enzyme molecule comprising two distinct zones: the binding site and the catalytic site. The active site incorporates specific segments of the polypeptide chain along with Cofactors. The interaction between the enzyme (E) and the substrate (S) yields an enzyme-substrate complex ES (1) (Fig. 2). Within this enzyme-substrate complex, the chemical bond is less stable than in the free substrate, which lowers the activation energy and leads to The formation of an activated enzyme-substrate complex ES' (2), thereby facilitating the reaction. In the subsequent stage, a chemical reaction takes place converting the substrate into a product (P), resulting in an enzyme-product complex EP (3). This is followed by the release of the reaction product or products (P) from the active site, while the enzyme is regenerated in its unchanged form (E).

Class="center">Fig. 2. METABOLISM/10.html">Mechanism of enzyme Action

As illustrated in Fig. 2, the enzyme and substrate fit together spatially like a lock and key.