HEPARIN-BINDING ASSAY OF VONWILLEBRAND-FACTOR (VWF) IN PLASMA MILIEU - EVIDENCE OF THE IMPORTANCE OF THE MULTIMERIZATION DEGREE OF VWF

We developed a simple and fast method for studying the heparin binding of von Willebrand factor (vWF) in the plasma milieu. Using plasma fro m patients with von Willebrand disease (vWD) subtype II, we found that the heparin binding was impaired when compared with a normal plasma c ontrol. Further experiments performed with purified vWF of various mul timeric composition, obtained either by gradual reduction or gel filtr ation, confirmed that heparin binding is dependent on the multimerizat ion of vWF and that high molecular weight (HMW) multimers of vWF are r equired for normal heparin binding. After reduction of plasma vWF by 1 .5 mM DTT, the vWF monomer still binds to heparin but to a lower exten t. Under these conditions, no significant differences were obtained be tween control and patients showing that the heparin binding domain loc ated on the vWF subunit is not altered in the subtypes IIA, IIB and II C studied.