The role of the lysine binding sites of human plasminogen in the fibrinogen stimulated rate of active site formation in the streptokinase-plasminogen equimolar complex.

The effect of various concentrations of epsilon-amino caproic acid (EACA) on the rate of active site formation in the human plasminogen moiety of the streptokinase-plasminogen equimolar complex has been studied in the absence and presence of human fibrinogen fragment D1 (FD1). In the absence of FD1, the pseudo first order rate constant (kobs) for active site development in this complex ranges from 8.4-17.9 x 10(-3) sec-1 with Glu1-plasminogen (Glu1-Pg), Lys77-plasminogen (Lys77-Pg), and Val442-plasminogen (Val442-Pg), at levels of EACA from 0-25 mM. In the presence of 2 microM FD1, the kobs for active site formation in the SK . Glu1-Pg complex, of 60.1 x 10(-3) sec-1, was not altered significantly as the EACA level was increased to 25 mM. Similarly, in the SK . Lys77-Pg complex, the kobs for active site formation, of 62.1 x 10(-3) sec-1, was essentially unchanged as the EACA level was increased to 25 mM. Finally, the kobs for active site formation in the SK . Val442-Pg complex, of 113.6 x 10(-3) sec-1, was also unaffected at levels of EACA up to 5 mM, with a slight inhibition at 25 mM EACA. These results show that the stimulation of active site formation in the equimolar Sk . Pg complex by fibrinogen fragment D1 is mediated by sites separate from the lysine binding sites of plasminogen.