The MMPs that are collagenases include: MMP-1 (collagenase-1) , MMP-8 (collagenase-2), MMP-13 (collagenase-3), and MMP-18 (Xenopus). The importance of these enzymes is their ability to cleave collagens I,II, and II at a specific site three-fourths from the N-terminus. It is important to note that collagenases can also digest other ECM and non-ECM molecules. During arthritis, MMP-1, MMP-8, and MMP-13 degrade type II collagen in cartilage.