What is the purpose of the formation of the ‘ES’ complex?

The substrate ‘S’ has to bind the enzyme at its ‘active site’ within a given cleft or pocket. The substrate has to diffuse towards the ‘active site’. There is thus, an obligatory formation of an ‘ES’ complex. E stands for enzyme. This complex formation is a transient phenomenon. During the state where substrate is bound to the enzyme active site, a new structure of the substrate called transition state structure is formed. The formation of the ‘ES’ complex, where E stands for enzyme, is mandatory for the catalyzation of the reaction. The complex formation helps in catalyzing the reaction.