title: Activation with plasmin of tow-chain urokinase-type plasminogen activator derived from single-chain urokinase-type plasminogen activator by treatment with thrombin.
abstract: Thrombin converts single-chain urokinase-type plasminogen activator (scu-PA) to an inactive two-chain derivative (thrombin-derived tcu-PA) by hydrolysis of the Arg-156--Phe-157 peptide bond. In the present study, we show that inactive thrombin-derived tcu-PA (specific activity 1000 IU/mg) can be converted with plasmin to active two-chain urokinase-type plasminogen activator (specific activity 43,000 IU/mg) by hydrolysis of the Lys-158--Ile-159 peptide bond. This conversion follows Michaelis-Menten kinetics with a Michaelis constant Km of 37 microM and a catalytic rate constant k2 of 0.013 s-1. The catalytic efficiency (k2/Km) for the activation of thrombin-derived tcu-PA by plasmin is about 500-fold lower than that for the conversion of intact scu-PA to tcu-PA. tcu-PA, generated by plasmin treatment of thrombin-derived tcu-PA, has similar properties to tcu-PA obtained by digestion of intact scu-PA with plasmin (plasmin-derived tcu-PA); its plasminogen activating potential and fibrinolytic activity in an in vitro plasma clot lysis system appear to be unaltered. These observations confirm that the structure of the NH2-terminal region of the B chain of u-PA is an important determinant for its enzymatic activity, whereas that of the COOH-terminal region of the A chain is not.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D004789:Enzyme Activation; D004926:Escherichia coli / Q000235:genetics; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D011994:Recombinant Proteins / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D011994:Recombinant Proteins; D013917:Thrombin; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator