A mutant of Schizosaccharomyces pombe deficient in both superoxide dismutase with copper and zinc as cofactors and glutathione was hypersensitive to menadione, which intracellularly generates superoxide radicals, and showed short chronological lifespan with more oxidation of proteins. Disruption of the sir2 gene in the double mutant enhanced the short chronological lifespan without more enhanced protein oxidation.