The region of an enzyme surface that binds the substrate molecule and transforms the substrate molecule into the new (chemical) product (entity). This site is usually located not on a protruding portion of the enzyme, but rather in a cleft or depression. This establishes a controlled environment in which the reaction may occur.
A three-dimensional region of a catalyst, receptor, or carrier where the substrate binds prior to catalysis, binding, or transport.
The reactive portion of an enzyme, in which the substrate molecules fit and form temporary bonds.