CAT and Parkinson disease: Ample of studies on postmortem brain tissues of PD patients has shown decreased levels of antioxidant enzyme activity (including GPx and CAT), reduced levels of GSH, elevated free iron levels, an augmented activity of SOD, and a decreased mitochondrial complex I activity in the SN of PD patients (Morris and Edwardson, 1994; Pearce et al., 1997; Blum et al., 2001; Jenner, 2003).