Glutathione and thioredoxin peroxidases mediate susceptibility of yeast mitochondria to Ca(2+)-induced damage.

The effect of thioredoxin peroxidases on the protection of Ca(2+)-induced inner mitochondrial membrane permeabilization was studied in the yeast Saccharomyces cerevisiae using null mutants for these genes. Since deletion of a gene can promote several other effects besides the absence of the respective protein, characterizations of the redox state of the mutant strains were performed. Whole cellular extracts from all the mutants presented lower capacity to decompose H(2)O(2) and lower GSH/GSSG ratios, as expected for strains deficient for peroxide-removing enzymes. Interestingly, when glutathione contents in mitochondrial pools were analyzed, all mutants presented lower GSH/GSSG ratios than wild-type cells, with the exception of DeltacTPxI strain (cells in which cytosolic thioredoxin peroxidase I gene was disrupted) that presented higher GSH/GSSG ratio. Low GSH/GSSG ratios in mitochondria increased the susceptibility of yeast to damage induced by Ca(2+) as determined by membrane potential and oxygen consumption experiments. However, H(2)O(2) removal activity appears also to be important for mitochondria protection against permeabilization because exogenously added catalase strongly inhibited loss of mitochondrial potential. Moreover, exogenously added recombinant peroxiredoxins prevented inner mitochondrial membrane permeabilization. GSH/GSSG ratios decreased after Ca(2+) addition, suggesting that reactive oxygen species (ROS) probably mediate this process. Taken together our results indicate that both mitochondrial glutathione pools and peroxide-removing enzymes are key components for the protection of yeast mitochondria against Ca(2+)-induced damage.