Isolation and partial purification of a novel anticoagulant from arteries of human umbilical cord

An anticoagulant fraction was isolated from the homogenate of human umbilical cord arteries, using Sephadex gel filtration and DEAE-Sephacel chromatography. Analysis with dodecyl sulfate/polyacrylamide gel electrophoresis and inactivation studies using proteolytic enzymes indicate that the anticoagulant activity is associated with a polypeptide with an apparent Mr of 32 000. The anticoagulant inhibits thromboplastin as well as factor Xa induced clotting but does not affect thrombin initiated fibrin formation. The anticoagulant inhibits the activation of prothrombin by the complete prothrombinase complex, by phospholipid bound factor Xa but not by free factor Xa. The inhibition is instantaneous and independent of the incubation time over the whole range of concentrations tested. Therefore, the anticoagulant is unlikely to be a phospholipase or a protease. Its action does not resemble that of the plasma protease inhibitors, but it probably interferes with the phospholipid--clotting factor interactions.