Fibrin degradation by t-PA–catalyzed plasmin digestion. Fibrinogen was clotted with thrombin and factor XIII in the presence of plasminogen (1.0 nmol/L), t-PA (4 U/mL), and CaCl₂. At 6 hours, 24 hours, 36 hours, and 48 hours, the reaction mixture was subjected to SDS-PAGE under reducing conditions.