Leupeptin is a competitive protease inhibitor produced by actinomycetes. Leupeptin can inhibit cysteine, serine and threonine peptidases. Leupeptin inhibits serine proteinases (trypsin (Ki=3.5 nM), plasmin (Ki= 3.4 nM), porcine kallikrein), and cysteine proteinases (papain, cathepsin B (Ki = 4.1 nM), endoproteinase Lys-C). Leupeptin does not inhibit alpha-chymotrypsin or thrombin.
