Purification and characterization of a new anticoagulant protein, PP27, from placenta

It has long been known that water extracts of placenta hominis (Jahage in Korean) are effective for treating immunological and vascular diseases and is a major constituent of traditional oriental medicines. We report herein on the isolation and purification of a new type of anticoagulant protein, PP27, from human placenta. PP27 ran as a single band on SDS-PAGE with a molecular mass (Mr) of 27 kDa under denaturing conditions and chromatography on a calibrated Sepharose 4B column indicated a molecular mass of 23 kDa, a value that is similar to those of other PP4 enzymes reported to date. The isoelectric point of PP27 was pI 5.2. PP27, at doses higher than 10 μg/ml, inhibited platelet activating factor (PAF)-induced platelet activation in a dose-dependent manner. The protein was found to inhibit the coagulation time in a concentration-dependent manner. PP27, which acts as a vascular anticoagulant of annexin type, inhibits the blood clotting process by virtue of its binding of essential lipids, which is dependent on the presence of Ca2+ ions. In the presence of Ca2+ ions, PP27 combines with platelet membranes and neutralizes their procoagulant effect. Coagulation, triggered by the addition of thromboplastin/lipid mixtures, is extinguished by PP27.