Metal ions can be involved in enzyme catalysis in a variety of ways.

1. They may accept or donate electrons to activate electrophiles or nucleophiles even in neutral solution.
2. They themselves act as neutrophiles.
3. They may mask nucleophiles to prevent unwanted side reaction.
4. They may bring together enzyme and substrate by means of coordinate bonds.
5. They may hold reacting groups in the required three-dimensional orientations.
6. They may catalytically active conformation of the enzyme.