Binding of rvWF mutants to heparin. Cell culture supernatant of cell lines producing rvWF was incubated with heparin-Sepharose in the presence of the indicated concentrations of NaCl. Unbound rvWF was measured in the supernatant, using an ELISA, after spinning down the heparin-Sepharose; WT-vWF (•), R543Q-vWF (▪), and R543W-vWF (□). The figure shows the curves of the mean ± SEM of three independent experiments.