Mitochondrial functionality. (A) Activity of succinate dehydrogenase (SDH) and of citrate synthase (CS) in the cellular extracts of control and transfected cells. Mean and SD from 8 experiments, expressed as units per milligram total proteins. (B) Total ATP content of the cells expressed as fold increase over the control, mock-transfected cells; mean and SD of 6 experiments; the difference was statistically significant (*P = .038). (C) Blotting analysis of frataxin expression in the control and transfected cells. Frataxin separates in a slower band corresponding to the mature form (m-Fxn) and a faster band corresponding to a degraded form (d-Fxn). In the silenced cells, the degraded form predominates. The relative content of total frataxin was evaluated by gel densitometry of 4 experiments as shown in the histogram. The difference was statistically significant (*P = .017). (D) Histogram of protoporphyrin fluorescence of HeLa cells before (−siRNA) and after (+siRNA) ABCB7 silencing. Data are representative of 4 independent experiments that showed an increase of 1.33-fold after silencing (P = .008).