Mechanism of Enzyme Action:

When the enzyme attaches to the substrate, a temporary enzyme-substrate (ES) complex is formed. The enzyme catalyzes the reaction and the substrate is transformed into a product. The ES complex breaks and enzymes and products are released.

Lock and Key Mechanism of Enzyme Action:

To explain the mechanism of enzyme action German chemist Emil Fischer, 1894, proposed the lock and key model. According to this model, both the and the substrate possess specific complementary geometric shapes that fit exactly into one another. This model explains enzyme specificity.

Modification of the Lock and Key Model: ("induced fit model").

The "induced fit model" is more acceptable than the "lock and key model. In 1958 an American biologist Daniel Koshland suggested a modification to the lock and key model and proposed the induced-fit model. He said that enzymes are flexible structures and their active site is reshaped as the substrate interacts with the enzyme. According to this model the active site is not a rigid structure rather it is molded into the precise position to perform its function.