A single mutation at the P1 position of PAI-1 alters the target specificity of PAI-1 from the plasminogen activators tPA and uPA to elastase. PAI-1 is normally a substrate for pancreatic and neutrophil elastase becoming cleaved at the P3 position. This mutant contains a P1 Alanine in place of the wild type Arginine residue resulting in an inhibitor of elastase as potent as alpha-1 PI (antitrypsin).