The site at which the substrate of an enzyme is bound during catalysis. Once bound, the substrate reacts to form a product or products, which are then released from the active site. The conformation and charge distribution of the active site is carefully tailored to accept only a specific substrate or class of substrates. Within the active site there are areas concerned with binding the substrate and other areas that create conditions conducive to the catalysis of substrate to products. The theory that best explains how the active site and the substrate interact is the induced fit hypothesis (see diagram). This considers the active site to be flexible and to adjust its conformation in response to the presence of a substrate molecule. The resulting distortion of both substrate and enzyme puts a strain on the substrate and is one factor contributing to the increased reaction rate.
Schematic representtion of the induced fit hypothesis.