293T cells treated with DMSO (B) or H2O2 (200 µM, 2 h) (D), were harvested for mitochondrial isolation. Purified mitochondria were treated with the indicated gradient concentration of proteinase K for 20 min on ice, and then were analyzed by Western blotting with anti-ATAD3, anti-Tom20 (OMM), anti-Tim23 (IMS), and anti-HSP60 (matrix). Relative protein levels of proteins in (B) or (D) were further evaluated by densitometry analysis using ImageJ software. Relative trends of proteolysis of indicated mitochondrial proteins from DMSO- or H2O2-treated cells were shown (C and E). Data are presented as mean ± SD (n = 3 independent experiments). 