Lock and Key Theory
The lock and key theory explains how enzymes are large globular proteins with specificity.
This theory was produced by Fischer and states that the enzyme’s active site and the substrate are complementary. Therefore, no change occurs to form the enzyme-substrate complex.
Induced fit model
The induced fit model was produced by Koshland, it is similar to the lock and key theory but it has some key differences.
It states that the presence of the substrate molecule in the active site induces a slight change in the shape of the active site. This causes it to mould around the substrate.
The enzyme does not undergo any permanent chemical changes during the reaction. Therefore, once the product detaches, it can catalyse another reaction with the same type of substrate molecule.