Activation of endosomal iPLA2 activity by ROSs. Endosomal vesicles were purified from reticulocytes and used to measure iPLA2 activity with the bodipy FL11 PC probe as described in “Measurement of iPLA₂ activity in endosomes.” (A) The enzymatic activity was measured in the absence (CTRL) or presence of the iPLA2-specific inhibitor bromoenolactone (BEL; 100μM). (B) Endosomal vesicles were incubated with H₂O₂ (3% and 15%) for 30 minutes before measuring iPLA2 activity. In some cases, vesicles were treated with BEL, as described in panel A, prior to H₂O₂ activation. Data are presented as means (± SD) of triplicate samples.