Anaerobic respiration of superoxide dismutase-deficient Saccharomyces cerevisiae under oxidative stress

The ethanol productivity of superoxide dismutase (SOD)-deficient mutants of Saccharomyces cerevisiae was examined under the oxidative stress by Paraquat. It was observed that MnSOD-deficient mutant of S. cerevisiae had higher ethanol productivity than wild type or CuZnSOD-deficient yeast both in aerobic and in anaerobic culture condition. Pyruvate dehydrogenase activity decreased by 35% and alcohol dehydrogenase activity increased by 32% were observed in MnSOD-deficient yeast grown aerobically. When generating oxygen radicals by Paraquat, the ethanol productivity was increased by 40% in CuZnSOD-deficient or wild strain, resulting from increased activity of alcohol dehydrogenase and decreased activity of pyruvate dehydrogenase. However, the addition of ascorbic acid with Paraquat returned the enzyme activities at the level of control. These results imply that SOD-deficiency in yeast strains may cause the metabolic flux to shift into anaerobic ethanol fermentation in order to avoid their oxidative damages by Paraquat.