A proteinase inhibitor from Caesalpinia echinata (pau-brasil) seeds for plasma kallikrein, plasmin and factor XIIa

Caesalpinia echinata is a tree belonging to the Leguminosae family. The red color of the trunk, looking like burning wood ('brasa' in Portuguese), is the origin of the name Brazil. Seeds of leguminous plants contain high amounts of serine proteinase inhibitors that can affect different biological processes. Here we show that a protein isolated from seeds of C. echinata is able to inhibit enzymes that participate in blood coagulation and fibrinolysis. This inhibitor (CeKI) was purified to homogeneity by ion exchange and reversed-phase chromatography. SDS-PAGE indicated a single polypeptide chain with a molecular mass of 20 kDa. CeKI inhibits human plasma kallikrein ( K i =3.1 nM), plasmin ( K i =0.18 nM), factor XIIa ( K i =0.18 nM), trypsin ( K i =21.5 nM) and factor Xa ( K i =0.49 mM). CeKI inhibited kinin release from highmolecular- mass kininogen by kallikrein in vitro . The N-terminal sequence, determined by automatic Edman degradation, identified the inhibitor as a member of the Kunitz family. The secondary structure, determined by circular dichroism, is mainly a random coil followed by beta-sheet structure. The action of CeKI on enzymes of the blood-clotting intrinsic pathway was confirmed by prolongation of the activated partial thromboplastin time.