Effects of HK peptides on the binding of kallikrein to HUVEC. HUVEC were incubated with 70 nmol/L HK in the presence of 50 μmol/L Zn²⁺. After washing, 10 nmol/L kallikrein was added in the absence or presence of HK peptide (0.53 μmol/L). After further washing, bound kallikrein was measured using S2302. Binding of kallikrein to cells in the absence of peptides was considered to be 100%. The data shown are the mean ± SEM of three experiments. HEPES-BSA containing ZnCl₂ (50 μmol/L) was used as the washing and assay buffers.