Enhanced Activator Activity of the Mixture of Streptokinase and a Modified Form of Plasminogen (Lys-Plasminogen) in the Presence of Fibrin: Role of Conformational Change of Plasminogen

Abstract

Equimolar concentrations of Lys-plasminogen (Lys-PLG) and streptokinase (SK) were mixed with various concentrations of fibrin, fibrinogen, fragment D or E (potentiating agents). The activity of the mixture was measured by the hydrolysis of S-2251. Kinetic analyses indicated that catalytic rate constant (k_cat) of the hydrolysis of S-2251 increased in the presence of increasing amounts of potentiating agents. K_m did not change in their presence. Effectiveness of the enhancement of the hydrolysis of S-2251 was in the order of fibrin > fibrinogen > E > D. It could be concluded that a complex of SK, Lys-PLG and potentiating agent is a better enzyme, thus activator, than a complex of SK and Lys-PLG. Since Lys-PLG does not change its conformation and its activation rate upon interaction with fibrin, the enhanced activator activity of complex of SK, Lys-PLG and potentiating agent may not be due to the conformational change of Lys-PLG.