An enzyme-catalyzed reaction takes place within the confined pocket on the enzyme called . Many enzymes require a non-protein accessory molecule or ion for their activity. The general term for such a component is __ . A non-protein accessory molecule that is very tightly or even covalently bound to the enzyme protein is called . A complete, catalytically active enzyme together with its bound accessory molecule is called a . The protein part of such an enzyme is called the .