Purification and Characterization of Two Related but Distinct Metalloproteinase Inhibitors Secreted by Bovine Aortic Endothelial Cells

Two metalloproteinase inhibitors were purified from serum-free medium conditioned by bovine aortic endothelial cells. One of these inhibitors, with a molecular weight of 30,000-34,000 (reduced) is identified as tissue inhibitor of metalloproteinases; the second inhibitor has a molecular weight of 27,500 (reduced) and 20,400 (unreduced), is not recognized by an antiserum against bovine tissue inhibitor of metalloproteinases, appears unglycosylated, and has 51% identity with tissue inhibitor of metalloproteinases by NH2-terminal amino acid sequence analysis. This inhibitor has antiproteinase activities similar to those of tissue inhibitor of metalloproteinases, with inhibition of classical collagenase, type IV collagenase, and gelatinases but not trypsin, plasmin, or bacterial collagenase. Other properties shared with tissue inhibitor of metalloproteinases include trypsin sensitivity, acid and heat resistance, and inactivation by reduction-alkylation. The presence of these inhibitors in endothelial cells suggests that they may play important roles in protecting the integrity of the vascular basement membrane.