Emil Fischer (1890) proposed a Lock and Key model to visualize substrate and enzyme interaction.
According to this model, as one specific key can open only a specific lock, similarly a specific enzyme can
(1) Lock and Key Model :
transforms only one substrate into products. According to Lock and Key model:
According to lock and key model The active site is a rigid (a) structure. enzyme acts as “key”.
.There is no modification or flexibility () in the active site before, during or after the enzyme action. Active site is used only as a template ). Later studies did not support this model in all reactions.
(ii) Induced Fit Model (Hands and Glove* Model):
On the basis of new evidences (), Koshland (1959) proposed modified G) form of Lock and Key model.
According to Induced Fit model:
When a substrate combines with an enzyme, it induces changes in the enzyme structure. The change in structure enables the enzyme to perform its catalytic activity more effectively.
According to this model enzymes are not rigid () and inflexible G), but are capable of considerable (E) internal movement.