Aiming to clarify the mechanisms by which eukaryotes acquire tolerance to oxidative stress, adaptive and cross-protection responses to oxidants were investigated in Saccharomyces cerevisiae. Cells treated with sub-lethal concentrations of menadione (a source of superoxide anions) exhibited cross-protection against lethal doses of peroxide; however, cells treated with H2O2 did not acquire tolerance to a menadione stress, indicating that menadione response encompasses H2O2 adaptation. Although, deficiency in cytoplasmic superoxide dismutase (Sod1) had not interfered with response to superoxide, cells deficient in glutathione (GSH) synthesis were not able to acquire tolerance to H2O2 when pretreated with menadione. These results suggest that GSH is an inducible part of the superoxide adaptive stress response, which correlates with a decrease in the levels of intracellular oxidation. On the other hand, neither the deficiency of Sod1 nor in GSH impaired the process of acquisition of tolerance to H2O2 achieved by a mild pretreatment with peroxide. Using a strain deficient in the cytosolic catalase, we were able to conclude that the reduction in lipid peroxidation levels produced by the adaptive treatment with H2O2 was dependent on this enzyme. Corroborating these results, the pretreatment with low concentrations of H2O2 promoted an increase in catalase activity.

The fermentation process offers a wide variety of stressors for yeast, such as temperature, aging, and ethanol. To evaluate a possible beneficial effect of trehalose on ethanol production, we used mutant strains of Saccharomyces cerevisiae possessing different deficiencies in the metabolism of this disaccharide: in synthesis, tps1; in transport, agt1; and in degradation, ath1 and nth1. According to our results, the tps1 mutant, the only strain tested unable to synthesize trehalose, showed the lowest fermentation yield, indicating that this sugar is important to improve ethanol production. At the end of the first fermentation cycle, only the strains deficient in transport and degradation maintained a significant level of the initial trehalose. The agt1, ath1, and nth1 strains showed the highest survival rates and the highest proportions of non-petites. Accumulation of petites during fermentation has been correlated to low ethanol production. When recycled back for a subsequent fermentation, those mutant strains produced the highest ethanol yields, suggesting that trehalose is required for improving fermentative capacity and longevity of yeasts, as well as their ability to withstand stressful industrial conditions. Finally, according to our results, the mechanism by which trehalose improves ethanol production seems to involve mainly protection against protein oxidation.

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Mutations in Cu, Zn-superoxide dismutase (Sod1) have been associated with familial amyotrophic lateral sclerosis, an age-related disease. Because several studies suggest that oxidative stress plays a central role in neurodegeneration, we aimed to investigate the role of the antioxidant glutathione (GSH) in the activation of human A4V Sod1 during chronological aging. Transformation of wild-type and A4V hSod1 into a gsh null mutant and in its parental strain of Saccharomyces cerevisiae indicated that during aging, the number of viable cells was strongly influenced by A4V hSod1 mainly in cells lacking GSH. Activity of hSod1 increased in response to aging, although the increase observed in A4V hSod1 was almost 60% lower. Activation of hSod1 (A4V and WT) did not occur after aging, in cells lacking GSH, but could still be observed in the absence of Ccs1. Furthermore, no increase in activity could be seen in grx1 and grx2 null mutants, suggesting that glutathionylation is essential for hSod1 activation. The A4V mutation as well as the absence of GSH, reduced hSod1 activity, and increased oxidative damage after aging. In conclusion, our results point to a GSH requirement for hSod1 Ccs1-independent activation as well as for protection of hSod1 during the aging process.