Fig. 25.2 A crystal structure of MMP-12 with both cleavage products has been determined (Fig. 25.1c). The cleavage product of the former N terminus (left, light-red carbon atoms) coordinates with its newly formed carboxylic acid function through an oxygen atom to the zinc ion and forms no hydrogen bonds to the enzyme itself. The cleavage product originating from the C terminus (right, light-green carbon atoms) forms four H-bonds to the main chain of the protein and binds with its P1′ residue in the deeply formed S1′ pocket. The released amino group coordinates to Glu219 and the water molecule that is bound to the zinc ion.