Characterization ofSaccharomyces cerevisiaeubiquinone‐deficient mutants

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Abstract
Ubiquinol (QH2) is a lipid‐soluble molecule that participates in cellular redox reactions. Previous studies have shown that yeast mutants lacking QH2are hypersensitive to treatment with polyunsaturated fatty acids (PUFAs) indicating that QH2can function as an antioxidant in vivo. In this study the effect of 1 mM linolenic acid on levels of Q6and Q6H2is assessed in both wild‐type and respiration‐deficient (atp2Δ) strains. The response of Q‐deficient mutants to other forms of oxidative stress is further characterized to define those conditions where QH2acts as an antioxidant. Endogenous antioxidant defense systems were also assessed in wild‐type, Q‐deficient, andatp2Δ strains. Superoxide dismutase (SOD) activity decreased and catalase activity increased in both Q‐deficient andatp2Δ mutants compared to wild‐type cells, suggesting that such changes result from the loss of respiration rather than the lack of Q.