Kinetics of inhibition of scuPA/suPAR activity by plasminogen kringle 1-3. (A) Dixon plot. The plasminogen activator activity of the scuPA/suPAR complex was measured in the presence of various concentrations of plasminogen kringle 1-3. The apparent Ki of kringle 1-3 is 1.9 μM. (B) Effect of kringle 1-3 on Km and Vmax of Glu-plasminogen activation by scuPA/suPAR at different concentrations of plasminogen. scuPA (10 nM) was incubated with an equimolar concentration of suPAR and Glu-plasminogen (8 nM-30 nM) in the presence (▵) or absence (□) of 1.9 μM K1-3. Plasmin activity is plotted as 1/velocity of the reaction versus 1/substrate concentration. The results shown are from one experiment representative of 2 performed.