Ristocetin, or botrocetin induced binding of rvWF mutants to fixed platelets. rvWF was incubated with formaldehyde fixed platelets in the presence of the indicated concentrations ristocetin (A) or botrocetin (B). Nonbound rvWF was measured in the supernatant, using an ELISA, after spinning down the platelets; WT-vWF (•), R543Q-vWF (▪), and R543W-vWF (□). The figures show the curves of the mean ± SEM of three independent experiments.