Enzyme Assay: Briefly, rPRCP was incubated in the presence or absence of various PRCP inhibitors in HEPES-carbonated buffer containing 1 mM Ala-Pro-paranitroaniline (APpNA, a PRCP chromogenic substrate). The final volume was 100 μL and the time of incubation was 60 min. Negative control had only 1 mM APpNA in HEPES-Carbonated buffer. Generation of free p-nitroaniline from APpNA was determined by monitoring changes in absorbance at 405 nm. Assays were done a minimum of 3 times.
Activation Assay: Human pulmonary artery endothelial cells (HPAEC) were purchased from Invitrogen (Carlsbad, Calif.) and were cultured as previously described.20 The cells were grown in Dulbecco's Modified Eagle's Medium (DMEM) overnight in 96 well plates (Costar). Cells were washed gently three times with HEPES-carbonated buffer (137 mM NaCl, 3 mM KCl, 12 mM NaHCO3, 14.7 mM HEPES, 5.5 mM Glucose, 0.1% Gelatin, 2 mM CaCl2, 1 mM MgCl2, 7.1 pH, 37° C.) between each incubation step. Gelatin blocking buffer (1% Gelatin) was prepared by adding appropriate amount of 5% gelatin stock to HEPES-carbonated buffer as described above. In the first step, gelatin blocking buffer was used to reduce the non specific binding. As part of this step, the cells were incubated with 1% gelatin buffer for 1 hour.