Summary
A method for the standardization of human plasminogen is proposed, based on the stoichiometric
interaction between plasminogen and streptokinase, resulting in inhibition of proteolytic
activity. Activation of a constant amount of plasminogen with increasing amounts of
streptokinase yields linearly decreasing activities, as a function of streptokinase,
with a sharp transition to a constant residual level. The point of transition corresponds
to complete saturation of plasmin with streptokinase in a 1:1 molar ratio, and is
therefore a measure of the amount of plasminogen present initially, in terms of streptokinase
equivalents. The equivalence point is independent of the kind of protein substrate
used, buffer, pH, length of digestion and, within limits, temperature. The method,
therefore, is not subject to the variations commonly encountered in the usual determination
based on specific activity measurements.
