A. Lysates from MCF-7 transfected with the empty vector (C), MCF-7 GPX1, MCF-7 MnSODVal and MCF-7 MnSODAla cell lines were used to determine GPX enzyme activity using a spectrophotometric assay that determines the GPX dependent consumption of NADPH. B. Lysates from MCF-7, GPX1, MnSODVal, and MnSODAla cells were analyzed for MnSOD protein levels by western blot using anti-MnSOD antibodies. β-Actin was used as an endogenous protein loading control. Protein levels were quantified using fluorescence detection and normalized to β-Actin. Error bars indicate the standard deviation (n=3) (* = p<0.05).