Enzyme attaches to substrate, forms enzyme-substrate complex, and catalyzes the reaction to form products. Then, enzyme is released to be reused.
In order to understand the mechanism of enzyme action two theories are proposed; Lock and key model and Induced fit model.
The Lock and Key theory, postulated by Emil Fischer in 1894, demonstrates enzyme specificity. Enzymes and substrates have complementary shapes that fit together like a lock and key. This theory explains how lipase and lipids fit together for breakdown. However, it does not explain the stabilization of the transition state achieved by enzymes.
The induced fit model proposed by Koshland in 1958 states that the active site of an enzyme is not a rigid structure, but rather a flexible one that changes its shape until the substrate fits into it. Unlike the lock and key model, this model accounts for the active site's flexibility.
