title: Functionally active thrombomodulin is present in human platelets.
abstract: We found functionally active thrombomodulin in human platelets (60 +/- 18 molecules per platelet). Protein C appeared not to be activated by thrombin with gel-filtered platelets. However, the activation of protein C by thrombin was accelerated by thrombin-stimulated and washed platelets. This cofactor activity of the platelets was neutralized by the anti-lung thrombomodulin-F(ab')2. From the Triton X-extract of platelets, thrombomodulin was partially purified by diisopropylphosphoryl-thrombin-agarose affinity chromatography. The Mr of the predominant platelet thrombomodulin was 78,000 before and 109,000 after reduction on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, values identical to those of placental thrombomodulin. The specific activity of the cofactor activity, apparent Kd (0.4 nM) for thrombin and Km (0.67 microM) for protein C of platelet thrombomodulin were also identical to those of placenta thrombomodulin. Thrombomodulin may play a role in activation of protein C on the surface of platelets.
authors.affiliation: Department of Laboratory Medicine, Mie University School of Medicine.
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.forename: J
authors.initials: J
authors.lastname: Nishioka
authors.forename: T
authors.initials: T
authors.lastname: Hayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Kosaka
mesh_terms: D001792:Blood Platelets / Q000032:analysis*; D002846:Chromatography, Affinity; D006801:Humans; D015151:Immunoblotting; D007124:Immunoenzyme Techniques; D007700:Kinetics; D011486:Protein C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000097:blood* / Q000302:isolation & purification; D018179:Receptors, Thrombin; D013917:Thrombin / Q000378:metabolism*
chemical_list: D011486:Protein C; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D013917:Thrombin