Cleavage of VWF multimer by rADAMTS13. The rADAMTS13 activity was measured by degradation of VWF multimers. The culture media of untransfected, WT, and the R193W mutant were incubated with purified VWF. The multimeric state of VWF was determined by Western blot analysis after SDS–agarose gel electrophoresis. The 1:4 diluted WT medium contained the enzyme amount roughly equivalent to the medium of the R193W mutant.