In this study, we used rADAMTS13 and pVWF as the sources of enzyme and substrate to determine the effect of SZ34 on VWF proteolysis under shear stress. The cleavage product was determined by SDS-PAGE under non-reducing conditions followed by Western blot. The results showed that the 350 kDa cleavage product of VWF under shear stress was reduced in the presence of SZ34 in a concentration-dependent manner ( Figure 1 ). The half maximal (50%) inhibitory concentration (IC 50 ) of the SZ34 was estimated to be approximately 50 mg/ml ( Figure 1 ). In contrast, other anti-VWF mAbs including 1C1E7 (an anti-VWF D'D3 mAb), SZ129 (an anti-VWF A1 mAb), SZ123 (an anti-VWF A3 mAb) and so on had no effects on the proteolytic cleavage of VWF by ADAMTS13 (Figure 1 and Table 1 ). The control experiments established the lack of detectable proteolysis in the absence of ADAMTS13 or in the addition of 20 mM EDTA to reaction mixtures ( Figure 1 ).