High levels of catalase in SOD mutants of Saccharomyces cerevisae in high aeration conditions

Saccharomyces cerevisiae mutants deficient in superoxide dismutase genes (sod1Δ, sod2Δ and sod1Δsod2Δ mutants) in a stationary phase of growth under high aeration conditions were subjected to H2O2 stress. All the mutants were sensitive after H2O2 treatment. Glutathione peroxidase levels were significantly lower in sod1Δ and sod2Δ single mutants than in the wild-type without treatment. After exposure to H2O2 concentrations, glutathione peroxidase levels were increased in sod1Δsod2Δ double mutants and the sod2Δ single mutant, while sod1Δ maintained lower gluthatione peroxidase activities. The sod2Δ mutant demonstrated a similar catalase activity to that of the wild-type without treatment, whilst decreased catalase activity was observed in conditions of low aeration. Untreated sod1Δsod2Δ double mutant cells presented a lower catalase activity. Catalase levels were higher under high aeration conditions than under microaerophilic conditions, including in sod1Δsod2Δ cells that contain less H2O2, since SOD catalyzes the cleavage of superoxide producing H2O2 and oxygen. We suggest that catalase is not essential for sod mutants under normal conditions, but plays an important role in the acquisition of tolerance to oxidative stress induced by high aeration