Isolation and properties of a thrombin-sensitive protein from human blood platelets.

A thrombin-sensitive protein has been isolated from human blood platelets by gel electrophoresis followed by filtration through Sephadex. The isolated protein was homogeneous on disc gel and behaved like a P-globulin. In immunoelectrophoresis, a single precipitin line was observed with antiplatelet serum or anti-fibrin-stabilizing factor serum. The precipitin line as well as the protein band on disc gel could not be detected when the protein was treated with thrombin. This protein, denoted platelet fibrin-stabilizing factor, has factor XIII activity which became more and more stable with further purification. Immunodifksion studies showed platelet fibrin-stabilizing factor to be only partially identical with plasma fibrin-stabilizing factor. The molecular weight of platelet fibrin-stabilizing factor as determined by gel IYtration through previously calibrated columns of Sephadex was between 110,000 and 150,000 compared to a value of 160,000 to 350,000 for plasma fibrin-stabilizing factor. It has been concluded that platelet fibrin-stabilizing factor is a smaller and di#erent molecule from plasma fibrin-stabilizing factor.