Investigation on the interaction of commercial forms of streptokinase and human plasminogen: a potential screening procedure for fibrinolytic inhibitors.

Streptokinase activation of human plasminogen is known to produce several enzymatic entities. Initially, the identification and characterization of these various entities were based on molecular model studies which necessitated highly purified biological materials and sophisticated techniques. However, these conditions cannot always be adhered to when alacrity, precision, and cost are often the prime factors governing the choice of a method for the evaluation of therapeutic agents. Our concern was therefore to find a suitable method of investigating inhibitors of the fibrinolytic system without compromising on accuracy, reliability, and reproducibility. We found that the activation of human plasminogen by streptokinase was dependent both on the duration of the activation step and the concentration of streptokinase used. By combining these two factors, activation could be visualized as a dual phase phenomenon. Each phase revealed distinct kinetic parameters and reactivity toward inhibitors such that their identity with the known enzymatic entities could be established. Inhibitors were further assessed with respect to their kinetic profile and were found to conform to known data. Therefore, the proposed method not only allows for direct visualization of the activation process but also meets the requirements for the routine screening of potential therapeutic inhibitors of the fibrinolytic system.