Effect of the A250V mutation on ADAMTS13 activity. The wild-type (WT) and A250V mutant ADAMTS13 were expressed in HEK293 cells. (A) The culture media and cell lysate were analyzed by Western blot. The molecular sizes as judged by protein standards are indicated at the left. (B) After normalization of ADAMTS13 protein concentration, the culture media were analyzed for the enzymatic activity by measuring the degradation of VWF multimers. The A250V mutant had markedly reduced activity compared with wild type.