Metalloproteinases (or metalloproteases) constitute a family of enzymes from the group of proteinases. There are two subgroups of metalloproteinases: metallocarboxipeptidases (EC number: 3.4.17) and metalloendopeptidases (3.4.24).

Proteinases can be divided into four families if we characterize them by the nature of the most prominent functional group in their active site: serine, cysteine, aspartic and metalloproteinases.

Metalloproteinases bind a metal ion such as Zn2+ or Ca2+ in their active site. The ion usually serves to coordinate two to four side chains and it is indispensable for the activity of the enzyme. The ion itself is also coordinated by a water molecule, which is also crucial for catalytical activity.

Important metalloproteinases are the bacterial enzyme thermolysin (which is a metalloendopeptidase), the digestive enzymes carboxipeptidase A or B (which are metallocarboxipeptidases), and the matrix metalloproteinases (MMP, also metalloendopeptidases).

MMPs play an important role in tumor metastasis, embryonic development, wound healing - generally in processes including matrix degradation. The proper functioning of MMPs involves the binding of Ca and Zn ions as well, but only the latter is bound in the active site of the enzyme, while Ca is only required for maintaining the molecule's conformation. There are about 20 discovered MMPs which bear strong structural similarities to each other, namely about 40% of amino acid homology. Some MMPs are extremely specific (like collegenase, which has only one target substrate), others have multiple substrates.