H2O2 generation in Saccharomyces cerevisiae respiratory pet mutants: effect of cytochrome c

Impaired electron transport chain function has been related to increases in reactive oxygen species (ROS) generation. Here we analyzed different pet mutants of Saccharomyces cerevisiae in order to determine the relative contribution of respiratory chain components in ROS generation and removal. We found that the maintenance of respiration strongly prevented mitochondrial H2O2 release and increased cellular H2O2 removal. Among all respiratory-deficient strains analyzed, cells lacking cytochrome c (cyc3 point mutants) presented the highest level of H2O2 synthesis, indicating that the absence of functional cytochrome c in mitochondria leads to oxidative stress. This finding was supported by the presence of high levels of catalase and peroxidase activity despite the lack of respiration. Furthermore, the addition of exogenous cytochrome c to isolated yeast mitoplasts significantly reduced H2O2 detection in a manner enhanced by cytochrome c reduction and the presence of a functional respiratory chain. Together, our results indicate that the maintenance of electron transport by cytochrome c prevents ROS generation by the respiratory chain.