Kinetic Studies of Three Different Molecular Forms of Urokinase for the Activation of Native Human Plasminogen

Abstract

The kinetic parameters of 3 different molecular forms of urokinase (UK) for the activation of native Glu-plasminogen were compared. The apparent Km (Km, app.) of each UK was almost of the same order of magnitude (31-38 .mu.M), but the catalytic constants (kc) were observed to be different: UKh (high MW form, MW 53,000), 2.4 .+-. 0.2 s-1; UKl (low MW form, MW 33,000), 0.83 .+-. 0.10 s-1, and UKt (trypsin-digested form, MW 36,000), 0.91 .+-. 0.18 s-1. The overall 2nd order rate constant, kc/Km calcualted for UKh was 7.7 .times. 104 M-1 s-1, higher than for UKl (2.2 .times. 104 M-1 s-1) or UKt (2.4 .times. 104 M-1 s-1), indicating the possibility of a much higher degree of enzymatic specificity and efficiency.