STUDIES OF THE PLASMIN SYSTEM

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Abstract
When plasminogen is separated quantitatively from serum by precipitation with the euglobulin fraction, inhibitors are left in the supernatant fluid. The content of human plasminogen may then be estimated from caseinolysis by plasmin after activation with 60 to 100 ug commercial streptokinase. There is a narrow concentration range of streptokinase for optimum activation of plasminogen. Because animal plasminogen is not directly activated by streptokinase, this same system can be used for measurement of animal plasminogen only when 0.05 ml human serum is added to furnish a coactivator for streptokinase. The coactivator capacity of an unknown human serum can also be measured by the ability of 0.02 ml serum to activate 0.5 ml guinea pig euglobulin during 5 minutes in the presence of streptokinase.