(A) Respiratory chain enzyme activities of control (blue), COX1∆ (red) and COX2∆ (green) cybrids. Enzyme activities were measured in three experimental replicates. Data are expressed as the percentages of control cells, and indicated as means ± SD. Mann-Whitney U test was applied for statistical analyses. Variations between controls and mutants: α, p<0.05; γ, p<0.001. Specific variations between COX1∆ and COX2∆ mutants: ∗p<0.05. 