C-D SDS-PAGE (C) and BN-PAGE (D) analyses from 143B cells and COX2∆ cybrids transiently transfected either with a COX5B-Myc-DDK construct or with the empty vector, followed by immunoblotting with antibodies against COX5B and CII subunit SDHA (loading control). The identities of MRC complexes and SCs are as in Figure 1. The red arrow points to the accumulation of over expressed COX5B bound to SC I+III2 in control cells. 