Thrombin-catalyzed fibrin polymerization. Polymerization of fibrinogen (0.17 mg/mL) was initiated with thrombin (0.05 U/mL) and the change in turbidity at 350 nm was followed with time. Representative polymerization curves for γ387I (♦), γ387R (▵), γ387L (▴), γ387M (▪), and γ387A (□) are shown.