Preparation of thrombomodulin from human placenta.

Thrombomodulin, a cell surface cofactor for thrombin-catalyzed activation of protein C, was isolated from human placenta by a combination of affinity chromatography and gel filtration. Molecular weight of purified human thrombomodulin, estimated by sodium dodecyl sulfate electrophoresis after reduction, was 88,000. Its isoelectric point was around pH 4. The thrombomodulin was soluble only in the presence of detergent. The purified thrombomodulin was inactivated by disulfide bond reduction, but was stable to heat, pH extremes and protein denaturants. The thrombomodulin served as a cofactor of thrombin-catalyzed protein C activation in human as well as bovine enzyme systems.