How many types of MMPs are there?

There are 28 distinct types of MMPs in vertebrates, in which 23 are expressed in human tissue. The types of MMPs are organized into 5 categories. One category is non-furin regulated MMPs (MMP-1, -3, -7, -8, -10, -12, -13, -20, and -27). The second category is MMPs consisting of three fibronectin-like inserts in the catalytic domain (MMP-2 and -9). The third category is MMPs anchored to the cellular membrane by a C-terminal glycophosphatidylinositol (MMP-11, -17, and -25). The fourth category is MMPs with a transmembrane domain (MMP -14, -15, -16, -24). The last category are all non classified MMPs (MMP -19, -21, -23, -26, and -28).