Amidolytic activity of HUVEC-bound kallikrein. HUVEC were incubated with 70 nmol/L HK in the presence (⊡, ▪) or absence (♦) of 50 μmol/L Zn²⁺. After washing, cells were further incubated in the presence (⊡, ♦) or absence (▪) of 10 nmol/L kallikrein. After additional washes, the amidolytic activity of cell-bound kallikrein was determined using S2302 (0.4 mmol/L). The data shown are from a single experiment run in triplicate of a total of three experiments. HEPES-BSA containing ZnCl₂ (50 μmol/L) was used as the washing and assay buffers.