Inactivation of genes encoding superoxide dismutase modifies yeast response to S-nitrosoglutathione-induced stress

Antioxidant enzymes can modify cell response to nitrosative stress induced, for example, by nitric oxide or compounds decomposing with its formation. Therefore, we investigated the effects of S-nitrosoglutathione (GSNO) on cell survival, activity of antioxidant enzymes, and concentrations of reduced and oxidized glutathione in parental and isogenic strains defective in Cu,Zn- or Mn-superoxide dismutases (Cu,Zn-SOD and Mn-SOD, respectively), or in both of them. Stress was induced by incubation of the yeast with 1-20 mM GSNO. The strains used demonstrated different sensitivity to GSNO. A Cu,Zn-SOD-defective strain survived the stress better than the parental strain, while the double mutant was the most sensitive to GSNO. The (*)NO-donor at low concentrations (1-5 mM) increased SOD activity, but its high concentrations (10 and 20 mM) decreased it. The activity of catalase in all strains was enhanced by GSNO. Inhibition of protein synthesis by cycloheximide did not prevent the activation of SOD, but it prevented the activation of catalase. These facts suggest that SOD was activated at a posttranslational level and catalase activity was enhanced via de novo synthesis. A GSNO-induced increase in oxidized glutathione level in the studied yeast strains might account for cell killing by GSNO due to the development of oxidative/nitrosative stress.