Kinetic properties of the activator complexes plasmin-staphylokinase and plasmin(ogen)-streptokinase in vitro

Comparative kinetic and electrophoretic study of the interaction of plasmin ogen (PG) with equimolar concentrations of staphylokinase (SPK) and strepto kinase (SK) at 4 and 37 degrees C showed that the PG-SK complex has fibrino lytic and esterase activities, whereas the PG-SPK complex was inactive. Bot h esterase and fibrinolytic activities were enhanced during the conversion of the PG-SPK complex to the complex of plasmin (PL) with SPK (PL-SPK) at 3 7 and 4 degrees C, while the PG-SK complex was rapidly converted to the PL- SK complex with higher esterase activity only at 37 degrees C. The catalyti c efficiency of Z-Lys-pNP hydrolysis (k(cat)/K-m) by the preformed PL-SPK c omplex was twofold lower than that in the case of the PL-SK complex. Incuba tion of the PL-SPK and PG-SK(PL-SK) complexes at 37 degrees C for 24 h was associated with the degradation of the proteins and with different kinetics of lowering of esterase, plasminogen activator, and fibrinolytic activitie s. The PL-SPK complex was considerably more stable than the PG-SK(PL-SK) co mplex; streptokinase degraded more rapidly than staphylokinase. Kinetics of lysis of fibrin clots by the two complexes were similar, but the efficienc y of lysis of plasma clots by the PL-SPK complex was significantly higher t han that in the case of the PG-SK(PL-SK) complex (at 0.03-1 mu M). Probably , unlike streptokinase, staphylokinase, which is less susceptible to degrad ation in the PL-SPK complex and is released from the triple complex alpha(2 )-antiplasmin-PL-SPK, forms a potentially highly active new complex with fr ee molecules of plasminogen in the plasma.