To validate protein abundance ratios measured by cICAT, we performed western blot analysis by using isolated r + and r 0 mitochondria and confirmed that the tested protein abundances were largely consistent with those measured by cICAT ( Figure 5 ). We selected eight up-regulated and nine down-regulated proteins from each functional module, of which antibodies were commercially available. We found that the levels of seven out of the eight up-regulated proteins were increased in r 0 mitochondria ( Figure 5A ). The up-regulated proteins were eIF4A1, PLG, HNRPM, XRCC6 (Ku70), XRCC5 (Ku80), APEX1, and STUB1. Likewise, the levels of all tested down-regulated proteins were decreased in r 0 mitochondria, consistent with the cICAT quantifications ( Figure 5B ). The down-regulated proteins were GTPBP3, NDUFS6, ATP5A1, ALDH6A1, GLUD1, MTRF1, TFAM, HSPD1 (HSP60), and ALDH2. The change of PARP1 levels was not detected by western blot. Additionally, the reliability of the protein expression patterns of cICAT was further confirmed by comparing the expression patterns of previously reported 2DE proteomic analyses [33] . Thirty of the 33 mt proteins (90.91%) identified from the 2DE proteomic analyses showed similar expression patterns compared to those obtained from the cICAT analysis ( Figure S2 ). The difference between protein expression patterns of cICAT and 2DE was insignificant (p-value was only 0.08).