Inactivation of Single - Chain Urokinase ( Pro - urokinase ) by Throm bin and Thrombin - like Enzymes : Relevance of the

Whereas crude bovine thrombin activated single-chain urokinase-type plasminogen activator (scu-PA), otherwise called pro-urokinase (pro-UK). purified human thrombin converted pro-UK (scu-PA) to a two-chain form that had no amidolytic activity. The two chains (M 33.000 and 22.000) were disulfide linked and resistant to subsequent activation by plasmin. By contrast. thrombin did not mactivate tissue plasminogen activator or two-chain urokinase. The enzyme from snake venom Agkistrodon contortrix, relatively specific for fibrinopeptide B. had an effect similar to thrombin, whereas the enzyme from Agkistrodon rhodostoma (ancrod). specific for fibrinopeptide A. did not. When pro-UK (scu-PA) was present during thrombin clotting of fibrinogen. degradation of 125l-pro-UK (scu-PA) in the clot supernatant was seen. whereas virtually full recovery (95%) of radioactivity was found. A loss of latent