PURIFICATION AND CHARACTERIZATION OF HUMAN PLATELET VON-WILLEBRAND-FACTOR

Platelet von Willebrand factor (vWf) was purified from human platelet concentrates. The multimeric structure of the purified platelet vWf wa s similar to that observed in the initial platelet lysate, and, like t he platelet lysate, the purified platelet vWf contained higher molecul ar weight multimers than plasma vWf. The apparent molecular weight of the reduced platelet vWf subunit was similar to the plasma vWf subunit . The N-terminal amino acid of the purified platelet and plasma vWf wa s blocked. In concentration dependent binding to botrocetin- or ristoc etin-stimulated platelets, I-125-plasma vWf bound with a higher affini ty than platelet. The ristocetin cofactor activity per mg of purified plasma vWf was 5-fold greater than the platelet vWf activity. Platelet and plasma vWf bound to collagen with similar affinities: however, pl atelet vWf bound to thrombin-stimulated platelets and to heparin with a higher affinity than plasma vWf. The differences in the binding affi nity(s) of plasma and platelet vWf to platelet GPIb and GPIIb/IIIa and extracellular matrix proteins may reflect different roles for plasma and platelet vWf in the initial stages of haemostasis and thrombosis.