Polymerization with fibrinogen-420 and fibrinogen-340. Polymerization was initiated by the addition of thrombin (0.1 U/mL) at time 0 to substrate at 0.1 mg/mL: either fibrinogen-340 (A) or fibrinogen-420 (B). Polymer formation was measured as change in turbidity at 350 nm with time as described in “Materials and methods.” Data in each panel are averages obtained from 4 separate trials. Bars indicate the standard deviation of the mean. For fibrinogen- 340 and fibrinogen-420, respectively, the lag periods were 8.0 ± 4.0 and 9.8 ± 4.6 minutes, and the maximum slopes were 7.3 ± 2.7 and 5.2 ± 3.7 × 10⁻⁵seconds⁻¹.