Comparison of the in vitro fibrinolytic activities of low and high molecular weight single-chain urokinase-type plasminogen activator.
The fibrinolytic activity of low molecular weight (LMW) single-chain urokinase-type plasminogen activator (scu-PA) lacking the epidermal growth factor domain and the kringle domain was compared with the activity of high molecular weight (HMW) scu-PA. LMW scu-PA was 1-5 times less active than HMW scu-PA in a fibrin plate method, in a purified fibrin clot lysis assay and in a plasma clot lysis assay. Time course experiments in a chromogenic plasminogen activator assay suggested that LMW scu-PA was less sensitive to activation by plasmin than HMW scu-PA. This was confirmed in a scu-PA activation test, which showed that at a concentration of 40 IU/ml LMW scu-PA required a three-fold higher plasmin concentration for 50% activation in 20 min than did HMW scu-PA. Kinetic experiments in the presence of 0.1 M NaCl showed non-standard Michaelis-Menten kinetics for the activation by plasmin of both HMW and LMW scu-PA. In contrast, standard kinetics was observed at 0.15 M NaCl, showing a 2.6-fold lower catalytic efficiency for LMW scu-PA than for HMW scu-PA. It is concluded that the plasmin activation of LMW scu-PA is about three times slower than the activation of HMW scu-PA. This explains, at least partially, the lower fibrinolytic activity of LMW scu-PA in comparison with HMW scu-PA.
de Munk
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GA
IVVO-TNO Gaubius Laboratory, Leiden, The Netherlands.
Groeneveld
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E
Rijken
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DC
D000595:Amino Acid Sequence; D002384:Catalysis; D002478:Cells, Cultured; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D014568:Urokinase-Type Plasminogen Activator / Q000737:chemistry / Q000378:metabolism*
D014568:Urokinase-Type Plasminogen Activator