Detection of plasminogen activator in macrophage culture supernatants by a photometric assay.

Plasminogen activator is usually detected indirectly through the lysis of radioiodinated fibrin. Here, it was investigated whether the fibrinolysis test may be substituted by a photometric assay using a synthetic chromogenic substrate (H-D-Val-Leu-Lys-p-nitroanilide; S-2251). Supernatants from cultured murine macrophages served as source of plasminogen activator. It is shown that under standard conditions the photometric assay is about twice as fast and 2--4-fold more sensitive than the fibrinolysis assay. Furthermore, reproducibility of the photometric test was found within 1.5--3.5% standard deviation compared to the fibrinolysis test which was found between 10--20% standard deviation.