Urokinase-catalysed plasminogen activation. Effects of ligands binding to the AH-site of plasminogen.
The kinetics of activation of Lys-plasminogen (Lys-77-Asn-790) and miniplasminogen (Val-442-Asn-790) catalysed by low-molecular-weight urokinase (LMW-urokinase) was investigated in the presence and absence of ligands that bind to the AH-site of the plasminogens. 6-Aminohexanoic acid and alpha-N-acetyl-L-lysine methyl ester (AcLysMe) were used. Saturation of the AH-sites of the plasminogens result in similar, but rather small positive effects on the kinetics of activation of the two plasminogens. Michaelis constants decrease approx. 2-fold and second-order rate constants (kc/Km)Pg increase approx. 1.2-fold. Michaelis constants (KPg values) were obtained using a new approach; the values were determined from the competing effects of the plasminogens on urokinase-catalysed hydrolysis of a synthetic substrate. In the pH range 7.4-8.0, only minor alterations of the values of the kinetic parameters are observed. At 25 degrees C, values of (kc/Km)Pg are approx. 3-fold less than the value at 37 degrees C, whereas KPg is not changed. We conclude that kc/Km values are approx. 10(5) M-1.s-1 and that KPg values are approx. 40 microM of urokinase-catalysed conversions of Lys- and miniplasminogen to their respective plasmins.
Christensen
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Chemical Laboratory 4, University of Copenhagen, Denmark.
D001665:Binding Sites; D004789:Enzyme Activation; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D009842:Oligopeptides / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors / Q000378:metabolism*
D008024:Ligands; D009842:Oligopeptides; D010958:Plasminogen; D014568:Urokinase-Type Plasminogen Activator