Specificity of rPRCP activity. (A) Ten nanomolar rPRCP in 0.2 M sodium acetate, 0.15 M KCl, pH 5.5, was treated with 10 nM to 10 mM DFP, PMSF, Z-Pro-Prolinal, leupeptin, or angiotensin II (AgII), and 3 mM H-Gly-Pro-pNA was added. The entire mixture was then transferred to a microtiter plate cuvette well, and hydrolysis was measured for 2 hours at 37°C. (B) Hydrolysis of 300 μM angiotensin II by 10 nM rPRCP(AgII + rPRCP) or 10 nM DFP-treated rPRCP (AgII + DFP-rPRCP). DFP-rPRCP was prepared by treating 10 nM rPRCP with 100 nM DFP followed by dialysis against HCB, pH 7.4, to eliminate the free DFP. The amount of residual angiotensin II after the various rPRCP treatments was measured by radioimmunoassay, as indicated in “Materials and methods.” In this experiment, angiotensin 1-7 (AgII1-7) was added at 300 μM. In both panels, the figure is the mean ± SEM of 3 or more experiments.