What are the main theoretical models that try to explain the formation of the enzyme-substrate complex?

There are two major models that explain the formation of the enzyme-substrate complex: the lock and key model and the induce fit model.

In the lock and key model the enzyme has a region with exact spatial conformation for the binding of the substrate. In the induced fit model the binding of the substrate induces a change in the spatial configuration of the enzyme for the substrate to fit.

Enzyme Activity: lock and key model induced fit model