Regulation of cell-associated scuPA by plasminogen. HUVECs were preincubated with glycine buffer, pH 3, washed, and PBS (Cont.) or PBS containing scuPA or tcuPA (5 nM) alone or in the presence of 1.5 μM K1-3. Glu-plasminogen (15 nM) and Spectrazyme PL (50 μM) were added for 20 minutes. The buffer was removed and the OD at 405 nm was measured.