VWF87(ΔSpacer) and VWF96-Cys proteolysis by ADAMTS13 in the presence and absence of mAbs. After preincubation of ADAMTS13_(V5-6xHis) with no mAb (orange; n = 3); the noninhibitory, nonactivating anti-Spacer domain mAb 15D1 (light green; n = 3); the activating anti-Spacer domain mAb 3E4 (red; n = 3); or the activating anti-CUB1 domain mAb 17G2 (blue; n = 3), the substrate (0.5 μM) was added to initiate the reaction. Reaction subsamples, stopped between 0 and 90 minutes, were analyzed by ELISA. Fitted time course data show the percentage of VWF87(ΔSpacer) (A) or VWF96-Cys (B) proteolysis as a function of time (mean ± standard error of the mean).