A mutation in succinate dehydrogenase cytochrome b causes oxidative stress and ageing in nematodes

Much attention has focused on the aetiology of oxidative damagein cellular and organismal ageing1,2,3,4. Especially toxic arethe reactive oxygen byproducts of respiration and other biological processes5. A mev-1 (kn1 ) mutant of Caenorhabditis elegans has been found to be hypersensitive to raised oxygen concentrations6,7. Unlike the wild type, its lifespan decreases dramatically as oxygen concentrations are increased from 1 to 60% (ref. 7). Strains bearing this mutation accumulate markers of ageing (such as fluorescent materials and protein carbonyls) faster than the wild type8,9. We show here that mev-1 encodes a subunit of the enzyme succinate dehydrogenase cytochrome b , which is a component of complex II of the mitochondrial electron transport chain. We found that the ability of complex II to catalyse electron transport from succinate to ubiquinone is compromised in mev-1 animals. This may cause an indirect increase in superoxide levels, which in turn leads to oxygen hypersensitivity and premature ageing. Our results indicate that mev-1 governs the rate of ageing by modulating the cellular response to oxidative stress.