Fig. 1.

Increased chronological life span of mutant Sir2 strains is not due to higher antioxidant capacity. Cultures of WT, C363S, C469S and C513S cells were grown in SC medium. (A) Viability was measured during chronological aging by plating serial dilutions (1:5) in YPD plates. (B) Growth curves were measured upon oxidative stress (0.5 mM or 1 mM H₂O₂), heat stress (38 °C or 39 °C) and osmotic stress (0.8 M or 1 M NaCl). The data are the averages of two independent experiments with two replicas each. (C) Catalase activity was analyzed in whole extracts from the exponential phase, days 1, 2 and 3 of culture. (D) Cell lysates from cultures at exponential phase, days 1 and 2 were analyzed by native electrophoresis and SOD staining. Total Coomassie blue protein staining was used as a loading control. Bands corresponding to MnSOD and Cu/ZnSOD activities were measured with a densitometer, and the relative intensity was calculated. (E) Cultures grown at exponential phase, days 1 and 5 were digested with nitric acid and total iron indicated with respect to the exponential WT strain. From C to E, statistical analysis was performed comparing mutant with WT cells. The data are represented as the means ± SD from at least three independent experiments.