A cyclopeptidic suicide substrate preferentially inactivates urokinase-type plasminogen activator.

Abstract c[Arg-aB-(CH 2 CH 3 φ)-Gly 4 ] was designed and studied as a mechanism-based inactivator (suicide substrate) for plasminogen activators (u-PA and t-PA) and plasmin. This compound inhibited u-PA and fulfills criteria expected for the involvement of an enzyme-activated inhibitor: first-order and irreversible process, saturation kinetics, protection by substrate. The limiting first-order rate constant k inact and the apparent enzyme-inhibitor dissociation constant K I were 0.021 s −1 and 9 μM, respectively at pH 7.5 and 25°C. The activation of plasminogen by u-PA is compromised after this enzyme has been treated by the reagent. Plasmin and t-PA were inactivated 40- and 2330-fold less efficiently than u-PA, respectively.