[Streptokinase and Staphylokinase: Differences in the Kinetics and Mechanism of Their Interaction with Plasminogen, Inhibitors and Fibrin]

Comparative in vitro study of the kinetics of various reactions involved in the process of thrombolysis initiated by streptokinase (SK) and staphylokinase (STA) was carried out. It was shown that at the interaction of an equimolar ratio of plasminogen (Pg) with SK or STA the rate of formation and the specific esterase activity of the complex plasmin (Pm) · SK are higher than those of the complex Pm · STA. The catalytic efficiency (kcat/Km) of hydrolysis of the chromogenic plasmin substrates by Pm · SK complex was 2 times higher than by Pm · STA complex. In the absence of fibrin catalytic efficiency (kPg/K(Pg)) of activation of Glu-plasminogen and Lys-plasminogen glycoform II by Pm · SK complex was higher than by Pm · STA complex, but the pres- ence of fibrin increased kPg/K(Pg)) activation of both plasminogens by Pm · STA complex significantly stronger than by Pm · SK complex due to the decrease in K(Pg)). In contrast to STA (15.5 kDa), SK molecule (47 kDa) creates significant steric hindrances for the interaction of plasmin in Pm · SK complex with protein inhibi- tors. In addition, SK caused greater fibrinogen degradation than STA. It is shown that Pm · SK and Pm · STA complexes lyse fibrin clots in buffer with similar rates, while the rate of lysis of plasma clots, immersed in plas- ma, by Pm · STA complex are significantly higher than those by Pm · SK complex. It was revealed that the species specificity of STA and S K is determined mainly by the rate of formation and the efficiency of Pm · SK and Pm · STA complexes in the activation of autologous plasminogen. The lysis efficiency of plasma clots of mammals fell in the series: human > dog > rabbit for SK and the dog > human > rabbit for STA. The results show that in the purified system SK is a more effective activator of plasminogen than STA. In the system con- taining fibrin and α2-AP, the activator and fibrinolytic activities of STA are higher than those of SK, due to the increased stability in plasma and fibrin specificity of STA, the fast reaction of the complex Pm · STA with α2AP and the ability of the STA to recyclization in the presence of α2AP.

[Covalent stretokinase-polyethylene glycol conjugates with increased stability and decreased side effects]

By variation of incubation time of streptokinase (SK) with activated polyethylene glycol (M 2 and 5 kDa, PEG2 and PEG5) it was obtained covalent SK-PEG2 and SK-PEG5 conjugates with different modification degrees of amino groups of protein and their properties were studied in vitro as compared with free SK. It was shown, that maximal stable and retaining 80% fibrinolytic activity SK-PEG2 and SK-PEG5 conjugates are formed when the modification degrees of amino groups of protein are 54 and 52%, respectively. At interaction of the given conjugates with equimolar plasminogen concentration it were formed the plasmin (Pm)·SK-PEG2 and Pm·SK-PEG5 activator complexes, the maximal amidase activity of which is equal to activity of unmodified Pm·SK complex. It was found, that the catalytic efficiency of plasminogen activation (kPg/KPg) by Pm·SK-PEG2 complex is some higher (2.84 min(-1) μM(-1)) and by Pm·SK-PEG5 complex is lower (1.17 min(-1) μM(-1)), than that by unmodified Pm·SK complex (2.1 min(-1) μM(-1)). Investigation of lysis kinetics of human plasma clots and depletion of plasminogen and fibrinogen in plasma under the action of free SK and SK-PEG2 and SK-PEG5 conjugates showed, that the latter's have high thrombolytic activity (89 and 72%, respectively) and cause 3.5-4 fold lower side effects, than free SK. Obtained by us SK-PEG2 and SK-PEG5 conjugates with increased stability and decreased side effects may be used in the therapy of thrombotic disorders.