(B) Digitonized mitochondria (digitonin-to-protein ratio of 2:1) were analyzed by BN-PAGE, followed by CI in gel activity (IGA) assays and Coomassie staining. The SC I+III2+IV1 band (b1) was excised from the control (143B) lane and the SC I+III2 bands (b2 to b4) were excised from the COX1∆ and COX2∆ lanes. Their protein compositions were subsequently analyzed by nano-LC/ESI-MS (see also Figure EV2). The relative position of the molecular weight marker is indicated on the left. 