The effect of HNE-treated F.IX and dEGR-F.IXa on the aPTT clotting activity of F.IXa. F.IX was treated with HNE or F.XIa (to generate F.IXa) as described in the Materials and Methods. A portion of the F.IXa reaction was further treated with dEGR-CMK to generate dEGR-F.IXa. The aPTT clotting activity of a fixed amount of F.IXa (10 pmol/L) was determined using varying amounts (0.01 to 10,000 pmol/L) of either HNE-treated F.IX (•) or dEGR-F.IXa (○) as competitor. A Log-Log plot of APTT clot time (in seconds) versus competitor concentration (in picomoles per liter) is shown.