Catalase activity is stimulated by H(2)O(2) in rich culture medium and is required for H(2)O(2) resistance and adaptation in yeast()

Catalases are efficient scavengers of H(2)O(2) and protect cells against H(2)O(2) stress. Examination of the H(2)O(2) stimulon in Saccharomyces cerevisiae revealed that the cytosolic catalase T (Ctt1) protein level increases 15-fold on H(2)O(2) challenge in synthetic complete media although previous work revealed that deletion of the CCT1 or CTA1 genes (encoding peroxisomal/mitochondrial catalase A) does not increase the H(2)O(2) sensitivity of yeast challenged in phosphate buffer (pH 7.4). This we attributed to our observation that catalase activity is depressed when yeast are challenged with H(2)O(2) in nutrient-poor media. Hence, we performed a systematic comparison of catalase activity and cell viability of wild-type yeast and of the single catalase knockouts, ctt1∆ and cta1∆, following H(2)O(2) challenge in nutrient-rich medium (YPD) and in phosphate buffer (pH 7.4). Ctt1 but not Cta1 activity is strongly induced by H(2)O(2) when cells are challenged in YPD but suppressed when cells are challenged in buffer. Consistent with the activity results, exponentially growing ctt1∆ cells in YPD are more sensitive to H(2)O(2) than wild-type or cta1∆ cells, whereas in buffer all three strains exhibit comparable H(2)O(2) hypersensitivity. Furthermore, catalase activity is increased during adaptation to sublethal H(2)O(2) concentrations in YPD but not in buffer. We conclude that induction of cytosolic Ctt1 activity is vital in protecting yeast against exogenous H(2)O(2) but this activity is inhibited by H(2)O(2) when cells are challenged in nutrient-free media.