Inhibition of scuPA-suPAR-mediated plasminogen activator activity by scuPA variants. Plasminogen activation was measured using a chromogenic assay. scuPA (2 nM) alone (▪) or complexed with 4 nM suPAR (□) was incubated in the absence and presence of 100-fold molar excess of GFD (▴), ATF 1-135 (▵), or scuPA-S³⁵⁶A (*). Glu-plasminogen (20 nM) and plasmin chromogenic substrate (500 μM) were added, and the optical density at 405 nm was measured continuously over time at 37°C. The data shown are from 1 experiment representative of 3 so performed.