FMO5 and Parkinson disease: Our previous studies in animal models of PD showed that AII, via cell surface AT1 receptors, increases oxidative stress through activation of membrane-bound NADPH oxidase.7, 9, 25 Within the mitochondria, the primary site of ROS generation is the ETC, as leakage of electrons at complexes I and III leads to a partial reduction of oxygen to form O2−.