Isolation, Partial Purification and Characterisation of A Plasminogen Activator Produced by Endothelial Cells in Vitro

Cloned endothelial cells obtained from the aorta of 1-2 day old calves produced high fibrinolytic activity, which was 90% dependent upon the presence of plasminogen when grown on 125 I fibrin coated dishes. High plasminogen-dependent proteolytic activity was also demonstrated in the cell lysate and in the culture medium of the cells. The production and secretion of this prtitease were found to increase during the log phase of cell growth and to reach a maximum at con fluency. Thereafter they remained constantly high. This protease, partially purified from the culture medium of confluent endothelial cell cultures, is aiginine specific and activates plasminogen by piOteolytic cleavage to plasmin. Its proteolytic activity which is highest in the pH range of 7.5 to 8.0 is irreversibly inhibited by diisopropyl fluorophosphate, suggesting that it is a serine protease. The molecular weight of this protease is approximately S2000.