Lock and Key model

In 1897, Email Fischer postulated a lock and key hypothesis to explain the interaction on between the enzyme molecule and substrate.

According to this model the activaste site of an enzyme is already exist in proper conformation even in the absence of substrate. The enzyme molecule itself provides a rigid, preshaped template fitting with the size and shape of the substrate molecule. The substrate fits into active site of an enzyme as key fixed into the lock and hence it is called as lock and key model but this model can not explain the change in the enzymatic interaction.