Binding of 99mTc plasminogen on fibrin

Binding of plasminogen to fibrin was studied in vitro and in vivo using 99mTc Glu- and Lys-plasminogen. Binding of Glu-plasminogen on the clot was not observed in vitro, and in vivo in the dog. Conversely, the binding of Lys-plasminogen to fibrin displays a linear relationship to the concentration of Lys-plasminogen, up to doses exceeding equimolarity; thus suggesting the existence of several Lys-plasminogen binding sites on fibrin. Binding levels were identical, regardless of whether plasminogen was incubated in normal plasma or in plasma devoid of antiplasmin. In the dog, Lys-plasminogen bound specifically to the clot, however, clot sites could not be localized by scintigraphy in the dog or in man.