Effect of phospholipids on the inhibition of tissue kallikrein by PCI. Tissue kallikrein (2 nM) was incubated for 60 minutes with PCI (45 nM) in the absence or presence of different concentrations of OxPAPS, PAPS (A), OxPAPE, PAPE (B), OxPAPC, PAPC (C), or heparin (D). Remaining tissue kallikrein activity was determined as described in “Materials and methods.” Each value represents the mean ± SEM of triplicate determinations.