CAT and B-cell chronic lymphocytic leukemia: On the other hand, to escape from the detrimental effect of overproduced O2−, CLL cells adopted a mechanism to eliminate O2− more efficiently by converting inactive SOD2 into a constitutively active enzyme via inducing SIRT3 expression, while maintaining low levels of catalase through variable degrees of promoter methylation for H2O2 accumulation to promote cell survival (Fig. 6).