Differential reactivity of Glu-Gly-Art-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 10⁴ 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 ... with K_i = 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 K_i = 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. [ABSTRACT FROM AUTHOR]