Figure 2. Demonstration of Catalase-specific activity in living cells.

(a) Immunofluorescence images of breast cancer cell line (MDA-MB-231) showing the spatial distribution of endogenous catalase in parental cells (231-P) and the lentiviral transduced overexpression (231-CAT). Co-staining with mitochondrial Complex II subunit shows that the overexpressed catalase is mainly localized in peroxisomal compartments with minimal colocalization in mitochondrial compartments. (b) Representative (n=4) oxygen concentration profiles upon H₂O₂ stimulus in 231-P and 231-CAT cells. In each case, 2.7 million viable living cells were added at the beginning of the experiment. (c) Summary of oxygen release rates (a measure of catalase activity) calculated from the above oxygen profiles. Note that the dramatic increase in oxygen release rate in 231-CAT cells is a clear illustration of the catalase-specific activity reported through out this paper. (d) Differential catalase activity (oxygen release rates) in non-transformed MCF10A epithelial cells and two representative human breast cancer cell lines. In contrast to the whole cells shown (b), only 50 μg of protein lysate was used for each cell line and the statistically significant increase in oxygen release rate further accentuates the high sensitivity in our measurement system.