Cleavage of ULVWF strings under flow in the absence of plasma. Recombinant ADAMTS-13 and 2 truncation mutants (A) were resuspended in the complete Tyrode buffer to a final concentration of 670 nM and perfused over histamine-stimulated HUVECs at a shear stress of 2.5 dyne/cm². (B) Perfusion of WT or MDTCS mutant resulted in 100% cleavage of ULVWF strings after 2-minute perfusion, whereas the cleavage by the MDTC mutant was significantly less. (C) The dose-dependent cleavage of ULVWF strings by WT ADAMTS-13 and the MDTCS mutant suspended in Tyrode buffer. At the concentrations of 42, 84, and 168 nM, the cleavage activity of the MDTCS mutant was significantly greater than that of WT. The figures are mean ± SEM; n = 96 for panel B and n = 9 for panel C; *P < .005 compared with WT.