Ctt1 activity is stimulated on H2O2 challenge in YPD and increases cell survival
We first compared catalase activity and cell viability after exposing wild-type YPH250 and wild-type BY4741 cells to increasing doses of H2O2 in nutrient-rich YPD media. Challenge of YPH250 cells with 0.2 and 0.4 mM H2O2 stimulates their catalase activity by 8- and 10-fold, respectively (Fig. 1A), and the cells remain 100% viable (Fig. 1B). Increasing the H2O2 dose to 1 mM and 2 mM results in weak catalase simulation and inhibition, respectively (Fig. 1 A) and a 50–80% drop in cell viability (Fig. 1B). Notably, H2O2 induces loss of viability in YPH250 cells with ~7 U of catalase activity per mg protein (Fig. 1 A) which, significantly, is also observed for wild-type BY4741 cells (Fig. 1C,D). In this strain the maximum stimulated catalase activity is close to 10 U per mg protein (Fig. 1C) and cells become sensitive to H2O2 at 0.4 mM (Fig. 1D). Interestingly, both strains require ~10 U of catalase activity per mg protein for protection against a bolus of H2O2 in the low millimolar range and, in the absence of catalase stimulation, the observed viability drops below 25% (Figs. 1 and 2). In sum, stimulation of catalase activity is required for protection of exponentially growing yeast against exogenous H2O2 and their enhanced catalase stimulation renders YPH250 cells more resistant to H2O2 than BY4741 cells (Fig. 1A,B vs. Fig. 1C,D).