Figure 1. Mutant cybrids lacking CIV display different SC I+III₂ species.

• A
  Mitochondrial extracts from 143B cells, and COX1Δ and COX2Δ mutant cybrids and their respective isogenic controls (CON‐1 and CON‐2) were analyzed by SDS–PAGE and immunoblotting with the indicated antibodies. The graphs (right) show densitometric quantifications of the signals normalized to CII subunit SDHA. The mean of three independent controls (CON) was set to 100, and all measurements were referenced to that value. The values represent mean ± SD (n = 3–8). Mann–Whitney U‐test was applied for statistical analyses. Variations between controls and mutants: α, P < 0.05; β, P < 0.01; and γ, P < 0.001. Specific variations between COX1Δ and COX2Δ mutants: *P < 0.05; **P < 0.01.
• 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 COX1Δ and COX2Δ lanes. Their protein compositions were subsequently analyzed by nano‐LC/ESI‐MS (see also Fig EV2). The relative position of the molecular weight marker is indicated on the left.
• C
  BN–PAGE was followed by CI‐IGA assay and immunoblotting with the indicated antibodies (in brackets). The identity of the MRC complexes and SCs is I+III₂+IV₁, SC containing CI, CIII₂, and CIV; I+III₂, SC containing CI and CIII₂; I+III_2plus, SC containing CI, CIII_2, and a COX1 submodule; III₂+IV, SC containing CIII₂ and CIV; I, complex I; III₂, CIII dimer; IV₂, CIV dimer; sub_COX1, COX1‐containing subcomplexes.

Data information: See also Figs EV1 and EV2.Source data are available online for this figure.