Simple and sensitive assay employing stable reagents for quantification of plasminogen activator

A simple and sensitive indirect assay for quantifying plasminogen activator using [3H]-casein as substrate is described. The assay has been used to measure plasminogen activators from various sources including bacteria, cultured cells, and human plasma. The assay is linear with respect to concentration of plasminogen activator and time of incubation and is independent of concentration of plasminogen. The assay can routinely be used to quantify as few as 8 X 10(-3) international units ml-1 of streptokinase. Results obtained with the [3H]-casein assay correlate well with those obtained by the fibrin plate method (R = 0.83 by Spearman's ranked co-efficient of correlation). The reagents are extremely stable and easily stored. The ease with which the assay can be performed gives the clinical laboratory the potential to test large numbers of patients upon short notice and within a short period of time.