The oxidation state of the cytoplasmic glutathione redox system does not correlate with replicative lifespan in yeast

Accumulating reactive oxygen species were proposed as leading cause of aging. Moreover, increasing pH in vacuole and cytosol was suggested to contribute to replicative aging in yeast, considered to be a model for aging stem cells. Here we investigated how cytosolic pH, H2O2 levels, and the glutathione redox buffer changes in aging yeast, using genetically encoded fluorescent probes and a newly developed flow-cytometry based aging assay. We found that pH decreases and H2O2 increases at the end of the replicative lifespan; but, surprisingly, the glutathione redox potential became more reducing in fermenting aged yeast cells in a glutareductase Glr1 dependent manner. Glr1 deletion leads to a highly oxidized cytosol but does not influence the replicative lifespan in liquid culture. Instead the end of lifespan seems to be marked by a break down of energy metabolism.