Inhibitors of platelet aggregation and blood coagulation isolated from the human placenta

We identified 2 potent proteins with inhibiting activities of platelet aggregation and blood coagulation from the human placenta. Ultracentrifugation of placental homogenate showed that these proteins are incorporated in the microsomal membrane. These proteins were solubilized in Triton X-100 by means of sonication. The inhibitors were purified by several steps of chromatography and gel filtration in a single band on polyacrylamide gel electrophoresis, having molecular weights of 450 000 and 45 000. The aggregation inhibitor was different from inhibitors reported previously such as phosphatase and prostacyclin-like substance. The coagulation inhibitor was capable of inactivating tissue thromboplastin.