Proenzyme to urokinase‐type plasminogen activator in the mouse in vivo

Abstract

We have investigated whether urokinase‐type plasminogen activator (u‐PA) is present in the mouse in vivo as the proenzyme or as the active enzyme. u‐PA in extracts of various murine tissues was of a one‐polypeptide chain form with an electrophoretic mobility indistinguishable from purified proenzyme (pro‐u‐PA), as demonstrated by SDS‐polyacrylamide gel electrophoresis under recucing conditions followed by immunoblotting. No 2‐chain u‐PA was detected in any of the extracts (detection limit 10% of that of one‐chain u‐PA). In bladder urine more than half of the u‐PA was of the one‐chain form. Together with previous immunocytochemical studies of the normal murine tissues and studies of the Lewis lung carcinoma, the present results indicate that in these tissues the one‐chain proenzyme is the predominant form of u‐PA in intracellular stores and for the first time demonstrates that at least in some cases the one‐chain form constitutes a sizeable fraction of the u‐AP in extracellular fluids in the intact organism.