Abstract
The oxygen dependence of cytochrome c oxidase control on succinate oxidation was investigated in saponin-permeabilized muscle fibers and isolated mitochondria from mouse quadriceps muscle applying metabolic control analysis. For this cyanide titrations of the oxygen consumption in the presence of succinate+rotenone were performed at different oxygen concentrations in the medium. While with isolated mitochondria high flux control coefficients were detected only at oxygen concentrations close to the K M value of cytochrome c oxidase, with saponin-permeabilized fibers a significant increase of cytochrome c oxidase flux control was already observed below 130 μM oxygen. The result is in line with the high oxygen sensitivity of maximal respiration of saponin-permeabilized muscle fibers (P 50=33 μM) caused most probably by oxygen diffusion gradients through the fiber lattice. The oxygen dependence of cytochrome c oxidase flux control in muscle fibers can explain the pathological phenotype of mild cytochrome c oxidase deficiencies in mitochondrial myopathies.
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