Western blot analysis of mitochondrial proteins. (A) Twenty micrograms of total cellular proteins from various cell lines were electrophoresed through a denaturing polyacrylamide gel, electroblotted and hybridized with 7 respiratory complex subunits in mutant and control cells with GAPDH as a loading control. p.MT-COI and p.MT-COII, indicate subunits I and II of cytochrome c oxidase; p.MT-ND1, p.MT-ND4 and p.MT-ND5, subunits 1, 4 and 5 of the reduced nicotinamide–adenine dinucleotide dehydrogenase; p.MT-ATP6, subunit 6 of the H±ATPase; and p.MT-CYTB, apocytochrome b. (B) Quantification of mitochondrial protein levels. Average relative p.MT-COI, p.MT-COII, p.MT-ND1, p.MT-ND4, p.MT-ND5, p.MT-ATP6 and p.MT-CYTB content per cell, normalized to the average content per cell of GAPDH in three mutant cell lines carrying the m.7551A > G mutation and three control cell lines lacking the mutation. The values for the latter are expressed as percentages of the average values for the control cell line. The calculations were based on three independent determinations. Graph details and symbols are explained in the legend to Figure 2.