Its uniqueness is caused by the sequence and nature of its amino acid side chains. It is this structure that allows an enzyme to perform its catalytic activity.
Enzyme molecules are, compared to most of their substrate molecules, rather large.
Their surface is not evenly structured but displays dent-ins, grooves, pockets, hollows etc. The part that binds to a substrate molecule is termed the active centre or substrate-binding site and is characterized by a shape complementary to that of the substrate molecule. Furthermore are certain amino acid side chains exposed at the active centre. They are engaged in the catalytic turn-over of the substrate. Numerous enzymes depend on additional factors that are necessary to perform the catalytic reaction.