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

Comparative kinetic and electrophoretic study of the interaction of plasminogen (PG) with equimolar concentrations of staphylokinase (SPK) and streptokinase (SK) at 4 and 37 degreesC showed that the PG--SK complex has fibrinolytic and esterase activities, whereas the PG--SPK complex was inactive. Both 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 37 and 4 degreesC, while the PG--SK complex was rapidly converted to the PL--SK complex with higher esterase activity only at 37 degreesC. The catalytic efficiency of Z-Lys-pNP hydrolysis (kcat/Km) by the preformed PL--SPK complex was twofold lower than that in the case of the PL--SK complex. Incubation of the PL--SPK and PG--SK(PL--SK) complexes at 37 degreesC for 24 h was associated with the degradation of the proteins and with different kinetics of lowering of esterase, plasminogen activator, and fibrinolytic activities. The PL--SPK complex was considerably more stable than the PG--SK(PL--SK) complex; streptokinase degraded more rapidly than staphylokinase. Kinetics of lysis of fibrin clots by the two complexes were similar, but the efficiency of lysis of plasma clots by the PL--SPK complex was significantly higher than that in the case of the PG--SK(PL--SK) complex (at 0.03-1 microM). Probably, unlike streptokinase, staphylokinase which is less susceptible to degradation in the PL--SPK complex and is released from the triple complex alpha2-antiplasmin--PL--SPK, forms a potentially highly active new complex with free molecules of plasminogen in the plasma.