The cleavage reactions were measured by the distribution of proteolytic fragments (350 kDa) on a 5% SDS-PAGE under nonreducing condition or by VWF multimeric size distribution on a 1.5% agarose gel electrophoresis, and then analyzed by Western blotting with HRP-conjugated anti-VWF IgG (Dako) and visualized by chemiluminescence as reported [23, 30] . The intensity of the bands was analyzed using Image J software. Plasmids encoding different VWF fragments were all generated from pSVHVWF1 [29] .