We have recently cloned MMP-19, a novel matrix metalloproteinase, which, due to unique structural features, was proposed to represent the first member of a new MMP subfamily (Pendá s, A. M., Knä uper, V., Puente, X. S., Llano, E., Mattei, M. G., Apte, S., Murphy, G., and Ló pez-Otin, C. -Pro-Leu-Gly-Dpa-Ala-Arg-NH 2 and, with higher efficiency, the stromelysin substrate McaPro-Leu-Ala-Nva-Dpa-Ala-Arg-NH 2 . Kinetic analysis of the interactions of the catalytic domain of MMP-19 with the natural MMP inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), showed strong inhibition using TIMP-2, TIMP-3, and TIMP-4, while TIMP-1 was less efficient. We also demonstrated that synthetic hydroxamic acid-based compounds efficiently inhibited the enzyme. The catalytic domain of MMP-19 was able to hydrolyze the basement membrane components type IV collagen, laminin, and nidogen, as well as the large tenascin-C isoform, fibronectin, and type I gelatin in vitro, suggesting that MMP-19 is a potent proteinase capable of hydrolyzing a broad range of extracellular matrix components. Neither the catalytic domain nor the fulllength MMP-19 was able to degrade triple-helical collagen. Finally, and in contrast to studies with other MMPs, MMP-19 catalytic domain was not able to activate any of the latent MMPs tested in vitro.