Comparison of the Gla-domains of plasma factor IX, wild-type factor IX, and factor IXR94S. (A) Increasing moles of factor IXpl (○), factor IXwt (•), or factor IXR94S (▴) were coated onto microtiter wells and then incubated with 15 μg/mL of IX/X-bp in the presence of 5 mmol/L Ca²⁺ in TBS. The binding of IX/X-bp to factor IX was measured by ELISA. The three factor IX proteins bound IX/X-bp equally well. (B) Binding of factor IX to 75:25 DOPC:DOPS vesicles. The three factor IX proteins bound phospholipid vesicles equally well. The bars and errors represent the mean and standard deviation (SD) of three experiments.