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

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 reducing 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.