Interaction of substrate and enzyme
The substrate interacts with the enzyme molecule in a region called the active site (center). It is formed as follows:
- Enzyme binding site
- The enzyme binding site is a spatially defined, small part of the enzyme molecule containing precisely distributed functional groups (−SH, −OH, acidic and basic amino acids ), whose position corresponds to the structure of the substrate. Non-bonding interactions (H-bridges, electrostatic and hydrophobic interactions, van der Waals forces) are involved in the binding between the enzyme and the substrate . Covalent bonds occur only exceptionally.
- A catalytic site
- The catalytic site contains other groups responsible for the catalytic activity of the enzyme. These groups often come from the cofactor molecule . However, the exact distinction between the binding and catalytic sites is usually problematic.
In addition to the active site, there may also be allosteric sites on the surface of the enzyme , enabling the regulation of enzyme activity due to various effectors (inhibitors or activators).
The original model of the interaction between the substrate molecule and the enzyme (later called the lock and key theory ) created by the German chemist Emil Hermann Fischer at the end of the 19th century assumed that the substrate molecule fits exactly into the enzyme molecule . In the 20th century, this model was modified by the American biochemist Daniel Edward Koshland, Jr., who came up with the claim that the substrate can to some extent induce a conformational change in the site to which it binds (or interact with each other). Therefore, the exact "lock and key" shape is achieved only after binding. It turns out that this induced fit theory describes the interactions between the enzyme and the substrate better than the original model .
