In biology, the
active site is the region of an
enzyme where
substrate molecules bind and undergo a
chemical reaction. The active site consists of
residues that form temporary bonds with the substrate (
binding site) and residues that catalyse a reaction of that substrate (catalytic site). The active site is usually a groove or pocket of the enzyme which can be located in a deep tunnel within the enzyme, or between the interfaces of
multimeric enzymes. An active site can
catalyse a reaction repeatedly as its residues are not altered at the end of the reaction (they may change during the reaction, but are regenerated by the end).