Binding of t-PA to non-crosslinked fibrin in a single perfusion. Radiolabeled, active-site blocked t-PA was perfused at a constant rate of 15 μL/min through a column of fibrin. The amount of bound t-PA was calculated by measuring radioactivity in aliquots of effluent from the column. Equilibrium was considered to occur when there was no additional binding of t-PA to the fibrin column as indicated by the flat portion of the curve. A single point representing mean equilibrium binding taken from that part of the curve was used for binding isotherms (Fig 3) and Scatchard analysis (Fig 4).