Evidence for a continuing accumulation of APSAC (Anisoylated plasminogen streptokinase activator complex) by human clots: Comparison with the binding of other plasminogen activators and Plasminogen

The uptake of [¹²⁵I-plasminogen]-APSAC into crosslinked human plasma clots from autologous plasma was significantly greater than the uptake of equimolar iodinated lys77-plasminogen. The uptake of APSAC in the presence of 6-aminohexanoic acid (10 mM) was also significantly greater than the uptake of plasminogen in the presence of 6-aminohexanoic acid.The accumulation of APSAC continued for at least 2 h (in nonlysing conditions), was similar in platelet-rich, platelet-poor and whole-blood clots and was not affected by prior aging of the clots (up to 6 h). The uptakes of APSAC and streptokinase plasminogen were slightly affected by the plasma concentration of anti-SK IgG and, in general, the fibrin-binding of APSAC was similar to the binding of radiolabelled t-PA. Urokinase (high-molecular weight) did not demonstrate fibrin- binding, the uptake being explained by simple diffusion (quantified using albumin). The relative order of continuing accumulation APSAC = t-PA > lys-plasminogen > urokinase is similar to the order of initial binding (< 1 min incubation), and we conclude that the formation of an acylated, stabilised, activator complex of lys-plasminogen and streptokinase imparts additional fibrin-binding to lys-plasminogen.