Matrix metalloproteinases are a family of zinc and calcium dependent endopeptidases with the combined ability to degrade all the components of the extracellular matrix. MMP-3 (stromelysin-1), can degrade a broad range of substrates including collagen alpha chains, aggrecan, laminin, fibronectin, and elastin. MMP-3 does not cleave the triple helical region of interstitial collagens, a characteristic which distinguishes the stromelysins from the collagenases. MMP-3 is expressed by fibroblasts, chrondrocytes, osteoblasts, endothelial cells, smooth muscle cells and macrophages. Structurally, MMP-3 may be divided into several distinct domains; a pro-domain which is cleaved upon activation; a catalytic domain containing the zinc binding site; a short hinge region and a carboxyl terminal (hemopexin-like) domain. The activity of recombinant human MMP-3 is measured by its ability to cleave a fluorogenic peptide substrate Mca-Arg-Pro-Lys-Pro-Val-Glu-Nval-Trp-Arg-Lys(Dnp)-NH2 in the assay buffer 50 mM Tris, 10 mM CaCl2, 150 mM NaCl, 0.05% (w/v) Brij-35, pH 7.5. The rhMMP3 is diluted to 200 ug/ml in assay buffer, then activated with 5 ug/ml chymotrypsin at 37 ℃ for 30min followed by adding 2 mM PMSF to stop activation. The activated rhMMP3 is diluted to 6.25 ug/mL in assay buffer. Loading into a black well plate 50 μL of 6.25 ug/mL rhMMP3 and start the reaction by adding 50 μL of 20 μM substrate, with a substrate blank containing 50 μL assay buffer, 50 μL substrate, and no rhMMP3. Then read at excitiation and emission wavelengths of 320 nm and 405 nm, respectively, in kinetic mode for 5 minutes. The specific activity of recombinant human MMP3 is > 90 pmol/min/μg.