MMP-3 is secreted from the cells as a proenzyme. The proenzyme has been shown to stimulate plasminogen activation. The N-terminal pro-domain contains the cysteine switch motif conserved in MMPs that maintains MMP-3 in the latent state. Activation of the proenzyme results in the removal of the pro-domain. MMP-3 activation can be achieved in vitro by proteases such as itself, chyrotrypsin, neutrophil elastase and plasma kallikrein, and by mercury compounds.

The resulting active enzyme consists of a catalytic domain with a zinc-binding motif conserved in metzincins. A short hinge peptide links the catalytic domain to the C-terminal hemopexin-like domain. The active MMP-3 is capable of cleaving types III, IV, IX and X collagen, aggrecan, fibronectin, laminin, IGFBP-3, serpins, and IL-1 .