MULTIMERIC STRUCTURE OF PLATELET FACTOR-VIII VONWILLEBRAND-FACTOR - THE PRESENCE OF LARGER MULTIMERS AND THEIR REASSOCIATION WITH THROMBIN-STIMULATED PLATELETS

Abstract

The multimeric structure of [human] platelet factor VIII/von Willebrand factor (FVIII/vWF) in cell extracts and in collagen and thrombin releasates was analyzed by SDS [sodium dodecyl sulfate] polyacrylamide gel electrophoresis followed by detection with 125I-anti-FVIII/vWF. Platelets contained larger multimers than those normally present in plasma. When secreted FVIII/vWF was analyzed, all platelet forms were released from collagen-stimulated platelets. In thrombin releasates the larger multimers were lost in a manner dependent on divalent cations, time and thrombin dose. This loss could not be accounted for by modification of FVIII/vWF by thrombin or platelet enzymes since no effect of thrombin on the multimeric structure of FVIII/vWF in the absence of platelets or in the presence of platelet lysates was observed. Large multimers of 125I-labeled purified FVIII/vWF underwent divalent cation-dependent association with platelets in the presence of thrombin, indicating that the loss of FVIII/vWF from thrombin releasates was due to reassociation with the platelet. A structural difference between platelet and plasma FVIII/vWF is shown that suggests a specific role for platelet FVIII/vWF in hemostasis.