Effect of HK peptides on activation of plasminogen. HUVEC were preincubated with HK (70 nmol/L) for 60 minutes at 4°C. After removing the residual HK, PK (50 nmol/L), HK peptide, plasminogen (60 nmol/L), prourokinase (4.5 nmol/L), and H-D-Val-Leu-Lys-amino methyl coumarin (50 μmol/L) were added and incubated at 23°C for 60 minutes. The plasmin activity is represented as nanomoles of substrate hydrolyzed per minute (mean ± SEM of 3 separate experiments).