Biochemical characterization of FIX-Padua (FIX-R338L). Data support that FIX-R338L requires factor VIIIa (FVIIIa) cofactor function for enzymatic activity to generate factor Xa (FXa) from FX and is similarly activated for factor XIa (FIXa) and inactivated by antithrombin (AT). Modified with permission from Samelson- Jones et al.⁷