Differential reactivity of Glu-Gly-Arg-CH2Cl, a synthetic urokinase inhibitor, with single-chain and two-chain forms of urokinase-type plasminogen activator.

Glu-Gly-Arg-CH2Cl, a synthetic inhibitor which alkylates the active-site histidine of urokinase with an apparent second-order rate constant of approximately 10(4) M-1 s-1, reacts differently with single-chain and two-chain forms of urokinase-type plasminogen activators (scu-PA and tcu-PA). Kinetic analysis indicated that the plasminogen activating potential of tcu-PA is irreversibly inhibited in a two-step reaction according to (formula; see text) with Ki = 5.0 X 10(-6) M and k2 = 0.05 s-1. The plasminogen-activating potential of scu-PA, however, is competitively inhibited by Glu-Gly-Arg-CH2Cl with Ki = 1.3 X 10(-6) M. Reversibility of the interaction of Glu-Gly-Arg-CH2Cl with scu-PA was confirmed by the restoration of full enzymatic activity after removal of inhibitor. The differential interaction of Glu-Gly-Arg-CH2Cl with scu-PA and tcu-PA supports the hypothesis that these molecular forms of urokinase-type PA have intrinsically different enzymatic properties.