Time course of fibrinopeptide release from fibrinogen 1 or fibrinogen 2 by thrombin. Reaction was initiated by the addition of thrombin (0.5 U/mL), and at selected intervals the reaction was terminated and fibrinopeptide release was quantified by HPLC. Fibrinogen 1: FPA (□); FPB (▪). Fibrinogen 2: FPA (○); FPB (•).