Effect of mutant ₂AP on whole-blood clot lysis. Whole blood containing ¹²⁵I-labeled fibrinogen and selected concentrations of mutant ₂AP and UK was clotted by the addition of thrombin and CaCl₂. Fibrinolysis was measured by counting radioactivity of the supernatant at each time point. It was expressed as the percentage of total radioactivity as described in Materials and Methods. Samples contained 40 U/mL UK alone (○), 40 U/mL UK and 0.25 μmol/L mutant ₂AP (•), 40 U/mL UK and 0.5 μmol/L mutant ₂AP (▴), 40 U/mL UK and 1.0 μmol/L mutant ₂AP (▪), and 80 U/mL UK alone (□). Each data point is the average of two experiments.