Injection and release of factor IX.

(A) Twelve-hour time-course of factor IX protein levels in the circulation. Factor IX knockout mice were injected with recombinant wild-type factor IX or its mutant with single amino acid substitutions in the Gla domain. In each case, factor IX or mutant was injected at zero time into the jugular vein to yield a concentration in plasma of 5 μg/mL. Samples were collected from the tail at 2, 10, 20, and 30 minutes and 1.5, 3, 6, 9, and 12 hours. The concentration of factor IX in plasma was determined by ELISA (n = 3). K5A (●), K5R (○), wild-type (▾). (B) Release of factor IX into circulation by EDTA. After 12 hours (A), EDTA was injected and the concentration of the factor IX was determined by ELISA (n = 3). (C) Volumes for a 2-compartment model of factor IX clearance. Data were analyzed by WinNonlin software. Ci, volume of the central compartment. Cii, volume of the second compartment. (D) Log concentration versus time for a 12-hour time-course. Time-courses of wild-type factor IX and mutant factor IX demonstrate a biphasic clearance, indicating a 2-compartment model of factor IX pharmacokinetics (symbols and data are the same as in panel A).