Jul 21, 2004

Inhibitors of the quinone-binding site allow rapid superoxide production from mitochondrial NADH:ubiquinone oxidoreductase (complex I)

The Journal of Biological Chemistry
Adrian J Lambert, Martin D Brand


Neither the route of electron transport nor the sites or mechanism of superoxide production in mitochondrial complex I has been established. We examined the rates of superoxide generation (measured as hydrogen peroxide production) by rat skeletal muscle mitochondria under a variety of conditions. The rate of superoxide production by complex I during NADH-linked forward electron transport was less than 10% of that during succinate-linked reverse electron transport even when complex I was fully reduced by pyruvate plus malate in the presence of the complex III inhibitor, stigmatellin. This asymmetry was not explained by differences in protonmotive force or its components. However, when inhibitors of the quinone-binding site of complex I were added in the presence of ATP to generate a pH gradient, there was a rapid rate of superoxide production by forward electron transport that was as great as the rate seen with reverse electron transport at the same pH gradient. These observations suggest that quinone-binding site inhibitors can make complex I adopt the highly radical-producing state that occurs during reverse electron transport. Despite complete inhibition of NADH: ubiquinone oxidoreductase activity in each case, different clas...Continue Reading

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Mentioned in this Paper

Ubiquinone (Lab Procedure)
Hydrogen Peroxide
Pyruvate Measurement
Electron Transport

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