Matrix metalloproteinases (MMPs) belong to a family of secreted or membrane-associated zinc endopeptidases capable of digesting extracellular matrix components. MMP-12 (macrophage elastase) is involved in smoke-induced emphysema, tumor and other diseases. MMP-12 is secreted as a 54 kDa zymogen and becomes the mature 54 kDa active form after proteolytic cleavage. MMP-12 has a broad range of substrates, including alpha-1 proteinase inhibitor, alpha-2 antiplasmin, plasminogen activator inhibitor-2, collagen IV, laminin, fibronectin, elastin, but not interstitial collagens.